Toward an Empirical Theory of Pulsar Emission. X. On the Precursor and Postcursor Emission

NARCIS (Netherlands)

Basu, R.; Mitra, D.; Rankin, J.M.

2015-01-01

Precursors and postcursors (PPCs) are rare emission components, which appear beyond the main pulse emission, in some cases far away from it, and are detected in a handful of pulsar. In this paper we attempt to characterize the PPC emission in relation to the pulsar main pulse geometry. In our

SEARCH FOR VERY HIGH ENERGY GAMMA-RAY EMISSION FROM PULSAR-PULSAR WIND NEBULA SYSTEMS WITH THE MAGIC TELESCOPE

International Nuclear Information System (INIS)

Anderhub, H.; Biland, A.; Antonelli, L. A.; Antoranz, P.; Balestra, S.; Barrio, J. A.; Bose, D.; Backes, M.; Becker, J. K.; Baixeras, C.; Bastieri, D.; Bock, R. K.; Gonzalez, J. Becerra; Bednarek, W.; Berger, K.; Bernardini, E.; Bonnoli, G.; Bordas, P.; Bosch-Ramon, V.; Tridon, D. Borla

2010-01-01

The MAGIC collaboration has searched for high-energy gamma-ray emission of some of the most promising pulsar candidates above an energy threshold of 50 GeV, an energy not reachable up to now by other ground-based instruments. Neither pulsed nor steady gamma-ray emission has been observed at energies of 100 GeV from the classical radio pulsars PSR J0205+6449 and PSR J2229+6114 (and their nebulae 3C58 and Boomerang, respectively) and the millisecond pulsar PSR J0218+4232. Here, we present the flux upper limits for these sources and discuss their implications in the context of current model predictions.

NEW DISCOVERIES FROM THE ARECIBO 327 MHz DRIFT PULSAR SURVEY RADIO TRANSIENT SEARCH

Energy Technology Data Exchange (ETDEWEB)

Deneva, J. S. [National Research Council, resident at the Naval Research Laboratory, Washington, DC 20375 (United States); Stovall, K. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States); McLaughlin, M. A.; Bagchi, M.; Garver-Daniels, N. [Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506 (United States); Bates, S. D. [The Institute of Mathematical Sciences, Chennai, 600113 (India); Freire, P. C. C.; Martinez, J. G. [Max-Planck-Institut für Radioastronomie, Bonn (Germany); Jenet, F. [Center for Advanced Radio Astronomy, Department of Physics and Astronomy, University of Texas at Brownsville, Brownsville, TX 78520 (United States)

2016-04-10

We present Clusterrank, a new algorithm for identifying dispersed astrophysical pulses. Such pulses are commonly detected from Galactic pulsars and rotating radio transients (RRATs), which are neutron stars with sporadic radio emission. More recently, isolated, highly dispersed pulses dubbed fast radio bursts (FRBs) have been identified as the potential signature of an extragalactic cataclysmic radio source distinct from pulsars and RRATs. Clusterrank helped us discover 14 pulsars and 8 RRATs in data from the Arecibo 327 MHz Drift Pulsar Survey (AO327). The new RRATs have DMs in the range 23.5–86.6 pc cm{sup −3} and periods in the range 0.172–3.901 s. The new pulsars have DMs in the range 23.6–133.3 pc cm{sup −3} and periods in the range 1.249–5.012 s, and include two nullers and a mode-switching object. We estimate an upper limit on the all-sky FRB rate of 10{sup 5} day{sup −1} for bursts with a width of 10 ms and flux density ≳83 mJy. The DMs of all new discoveries are consistent with a Galactic origin. In comparing statistics of the new RRATs with sources from the RRATalog, we find that both sets are drawn from the same period distribution. In contrast, we find that the period distribution of the new pulsars is different from the period distributions of canonical pulsars in the ATNF catalog or pulsars found in AO327 data by a periodicity search. This indicates that Clusterrank is a powerful complement to periodicity searches and uncovers a subset of the pulsar population that has so far been underrepresented in survey results and therefore in Galactic pulsar population models.

NEW DISCOVERIES FROM THE ARECIBO 327 MHz DRIFT PULSAR SURVEY RADIO TRANSIENT SEARCH

International Nuclear Information System (INIS)

Deneva, J. S.; Stovall, K.; McLaughlin, M. A.; Bagchi, M.; Garver-Daniels, N.; Bates, S. D.; Freire, P. C. C.; Martinez, J. G.; Jenet, F.

2016-01-01

We present Clusterrank, a new algorithm for identifying dispersed astrophysical pulses. Such pulses are commonly detected from Galactic pulsars and rotating radio transients (RRATs), which are neutron stars with sporadic radio emission. More recently, isolated, highly dispersed pulses dubbed fast radio bursts (FRBs) have been identified as the potential signature of an extragalactic cataclysmic radio source distinct from pulsars and RRATs. Clusterrank helped us discover 14 pulsars and 8 RRATs in data from the Arecibo 327 MHz Drift Pulsar Survey (AO327). The new RRATs have DMs in the range 23.5–86.6 pc cm −3 and periods in the range 0.172–3.901 s. The new pulsars have DMs in the range 23.6–133.3 pc cm −3 and periods in the range 1.249–5.012 s, and include two nullers and a mode-switching object. We estimate an upper limit on the all-sky FRB rate of 10 5  day −1 for bursts with a width of 10 ms and flux density ≳83 mJy. The DMs of all new discoveries are consistent with a Galactic origin. In comparing statistics of the new RRATs with sources from the RRATalog, we find that both sets are drawn from the same period distribution. In contrast, we find that the period distribution of the new pulsars is different from the period distributions of canonical pulsars in the ATNF catalog or pulsars found in AO327 data by a periodicity search. This indicates that Clusterrank is a powerful complement to periodicity searches and uncovers a subset of the pulsar population that has so far been underrepresented in survey results and therefore in Galactic pulsar population models

The Frequency Evolution of Interstellar Pulse Broadening from Radio Pulsars

Science.gov (United States)

Löhmer, O.; Mitra, D.; Gupta, Y.; Kramer, M.; Ahuja, A.

2004-10-01

Using radio pulsars as probes of the interstellar medium (ISM) we study the frequency evolution of interstellar scattering. The frequency dependence of scatter broadening times, τsc, for most of the pulsars with low and intermediate dispersion measures (DM ≲ 400 pc cm-3) is consistent with the Kolmogorov spectrum of electron density fluctuations in a turbulent medium. In contrast, the measured τsc's for highly dispersed pulsars in the central region of the Galaxy are larger than expected and show a spectrum which is flatter than the Kolmogorov law. We analyse the first measurements of spectral indices of scatter broadening over the full known DM range and discuss possible explanations for the anomalous scattering behaviour along peculiar lines of sight (LOS).

Limits on an optical pulsar in supernova 1987A

International Nuclear Information System (INIS)

Pennypacker, C.R.; Morris, D.E.; Muller, R.A.

1989-01-01

Since March 1987 the optical flux from supernova 1987A for periodic pulsations has been sought. As of August 1988, after 38 separate observations, no pulsar has been detected. The typical upper limit placed on the pulsed fraction optical light from the supernova is 0.0002, for pulse frequencies in the range 0.03-5000 Hz. The best limit on the pulsed fraction of supernova light is 7 x 10 to the -6th, on January 22, 1988. On August 28, 1988 the faintest limit for the magnitude of the pulsar, dimmer than 20th mag is reached. These limits are based on Fourier transforms of up to 67 million points, covering a range of spindown rates. 25 refs

CORRELATION OF FERMI PHOTONS WITH HIGH-FREQUENCY RADIO GIANT PULSES FROM THE CRAB PULSAR

International Nuclear Information System (INIS)

Bilous, A. V.; Kondratiev, V. I.; McLaughlin, M. A.; Mickaliger, M.; Ransom, S. M.; Lyutikov, M.; Langston, G. I.

2011-01-01

To constrain the giant pulse (GP) emission mechanism and test the model of Lyutikov for GP emission, we have carried out a campaign of simultaneous observations of the Crab pulsar at γ-ray (Fermi) and radio (Green Bank Telescope) wavelengths. Over 10 hr of simultaneous observations we obtained a sample of 2.1 x 10 4 GPs, observed at a radio frequency of 9 GHz, and 77 Fermi photons, with energies between 100 MeV and 5 GeV. The majority of GPs came from the interpulse (IP) phase window. We found no change in the GP generation rate within 10-120 s windows at lags of up to ±40 minutes of observed γ-ray photons. The 95% upper limit for a γ-ray flux enhancement in pulsed emission phase window around all GPs is four times the average pulsed γ-ray flux from the Crab. For the subset of IP GPs, the enhancement upper limit, within the IP emission window, is 12 times the average pulsed γ-ray flux. These results suggest that GPs, at least high-frequency IP GPs, are due to changes in coherence of radio emission rather than an overall increase in the magnetospheric particle density.

COBRA: a Bayesian approach to pulsar searching

Science.gov (United States)

Lentati, L.; Champion, D. J.; Kramer, M.; Barr, E.; Torne, P.

2018-02-01

We introduce COBRA, a GPU-accelerated Bayesian analysis package for performing pulsar searching, that uses candidates from traditional search techniques to set the prior used for the periodicity of the source, and performs a blind search in all remaining parameters. COBRA incorporates models for both isolated and accelerated systems, as well as both Keplerian and relativistic binaries, and exploits pulse phase information to combine search epochs coherently, over time, frequency or across multiple telescopes. We demonstrate the efficacy of our approach in a series of simulations that challenge typical search techniques, including highly aliased signals, and relativistic binary systems. In the most extreme case, we simulate an 8 h observation containing 24 orbits of a pulsar in a binary with a 30 M⊙ companion. Even in this scenario we show that we can build up from an initial low-significance candidate, to fully recovering the signal. We also apply the method to survey data of three pulsars from the globular cluster 47Tuc: PSRs J0024-7204D, J0023-7203J and J0024-7204R. This final pulsar is in a 1.6 h binary, the shortest of any pulsar in 47Tuc, and additionally shows significant scintillation. By allowing the amplitude of the source to vary as a function of time, however, we show that we are able to obtain optimal combinations of such noisy data. We also demonstrate the ability of COBRA to perform high-precision pulsar timing directly on the single pulse survey data, and obtain a 95 per cent upper limit on the eccentricity of PSR J0024-7204R of εb < 0.0007.

Elementary wideband timing of radio pulsars

Energy Technology Data Exchange (ETDEWEB)

Pennucci, Timothy T. [University of Virginia, Department of Astronomy, P.O. Box 400325 Charlottesville, VA 22904-4325 (United States); Demorest, Paul B.; Ransom, Scott M., E-mail: pennucci@virginia.edu, E-mail: pdemores@nrao.edu, E-mail: sransom@nrao.edu [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States)

2014-08-01

We present an algorithm for the simultaneous measurement of a pulse time-of-arrival (TOA) and dispersion measure (DM) from folded wideband pulsar data. We extend the prescription from Taylor's 1992 work to accommodate a general two-dimensional template 'portrait', the alignment of which can be used to measure a pulse phase and DM. We show that there is a dedispersion reference frequency that removes the covariance between these two quantities and note that the recovered pulse profile scaling amplitudes can provide useful information. We experiment with pulse modeling by using a Gaussian-component scheme that allows for independent component evolution with frequency, a 'fiducial component', and the inclusion of scattering. We showcase the algorithm using our publicly available code on three years of wideband data from the bright millisecond pulsar J1824–2452A (M28A) from the Green Bank Telescope, and a suite of Monte Carlo analyses validates the algorithm. By using a simple model portrait of M28A, we obtain DM trends comparable to those measured by more standard methods, with improved TOA and DM precisions by factors of a few. Measurements from our algorithm will yield precisions at least as good as those from traditional techniques, but is prone to fewer systematic effects and is without ad hoc parameters. A broad application of this new method for dispersion measure tracking with modern large-bandwidth observing systems should improve the timing residuals for pulsar timing array experiments, such as the North American Nanohertz Observatory for Gravitational Waves.

The development of 128 ch fast multi channel pulse height analyzer for a tokamak plasmas

International Nuclear Information System (INIS)

Kawashima, Hisato; Matoba, Tohru; Ogawa, Toshihide; Kawakami, Tomohide

1985-02-01

A high counting rate multi channel pulse height analyzer was developed and tested to measure the detailed time evolution of X-ray energy spectrun radiated from a tokamak plasmas. Main developing objects of this analyzer are as follows. 1. The maximum counting rate and the minimum time resolution are 4 Mcps and 10 ms, respectively. 2. The energy resolution has ability to distinguish the characterisitic X-ray line. 3. Computer has to be used for operating system. This fast multi channel analyzer is using to measure the Soft X-ray spectrum on JFT-2M tokamak, and is confirmed to be useful for a practical measuring system. (author)

Phase-resolved X-ray polarimetry of the Crab pulsar with the AstroSat CZT Imager

Science.gov (United States)

Vadawale, S. V.; Chattopadhyay, T.; Mithun, N. P. S.; Rao, A. R.; Bhattacharya, D.; Vibhute, A.; Bhalerao, V. B.; Dewangan, G. C.; Misra, R.; Paul, B.; Basu, A.; Joshi, B. C.; Sreekumar, S.; Samuel, E.; Priya, P.; Vinod, P.; Seetha, S.

2018-01-01

The Crab pulsar is a typical example of a young, rapidly spinning, strongly magnetized neutron star that generates broadband electromagnetic radiation by accelerating charged particles to near light speeds in its magnetosphere1. Details of this emission process so far remain poorly understood. Measurement of polarization in X-rays, particularly as a function of pulse phase, is thought to be a key element necessary to unravel the mystery of pulsar radiation2-4. Such measurements are extremely difficult, however: to date, Crab is the only pulsar to have been detected in polarized X-rays5-8 and the measurements have not been sensitive enough to adequately reveal the variation of polarization characteristics across the pulse7. Here, we present the most sensitive measurement to date of polarized hard X-ray emission from the Crab pulsar and nebula in the 100-380 keV band, using the Cadmium-Zinc-Telluride Imager9 instrument on-board the Indian astronomy satellite AstroSat10. We confirm with high significance the earlier indication6,7 of a strongly polarized off-pulse emission. However, we also find a variation in polarization properties within the off-pulse region. In addition, our data hint at a swing of the polarization angle across the pulse peaks. This behaviour cannot be fully explained by the existing theoretical models of high-energy emission from pulsars.

Pulsed time-of-flight refractometry measurements of the electron density in the T-11M tokamak

International Nuclear Information System (INIS)

Petrov, A.A.; Petrov, V.G.; Malyshev, A.Yu.; Markov, V.K.; Babarykin, A.V.

2002-01-01

A new method for measuring the plasma density in magnetic confinement systems - pulsed time-of-flight refractometry - is developed and tested experimentally in the T-11M tokamak. The method is based on the measurements of the time delay of short (with a duration of several nanoseconds) microwave pulses propagating through the plasma. When the probing frequency is much higher than the plasma frequency, the measured delay in the propagation time is proportional to the line-averaged electron density regardless of the density profile. A key problem in such measurements is the short time delay of the pulse in the plasma (∼1 ns or less for small devices) and, consequently, low accuracy of the measurements of the average density. Various methods for improving the accuracy of such measurements are proposed and implemented in the T-11M experiments. The measurements of the line-averaged density in the T-11M tokamak in the low-density plasma regime are performed. The results obtained agree satisfactorily with interferometric data. The measurement errors are analyzed, and the possibility of using this technique to measure the electron density profile and the position of the plasma column is discussed

THE SECOND FERMI LARGE AREA TELESCOPE CATALOG OF GAMMA-RAY PULSARS

Energy Technology Data Exchange (ETDEWEB)

Abdo, A. A. [Center for Earth Observing and Space Research, College of Science, George Mason University, Fairfax, VA 22030 (United States); Ajello, M. [Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States); Allafort, A.; Bloom, E. D.; Bottacini, E. [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States); Baldini, L. [Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy); Ballet, J. [Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d' Astrophysique, CEA Saclay, F-91191 Gif sur Yvette (France); Barbiellini, G. [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy); Baring, M. G. [Rice University, Department of Physics and Astronomy, MS-108, P.O. Box 1892, Houston, TX 77251 (United States); Bastieri, D. [Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy); Belfiore, A. [Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Bellazzini, R.; Bregeon, J. [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy); Bhattacharyya, B. [National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune 411 007 (India); Bissaldi, E. [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, and Università di Trieste, I-34127 Trieste (Italy); Bonamente, E. [Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy); Brandt, T. J. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Brigida, M., E-mail: hartog@stanford.edu [Dipartimento di Fisica ' ' M. Merlin' ' dell' Università e del Politecnico di Bari, I-70126 Bari (Italy); and others

2013-10-01

This catalog summarizes 117 high-confidence ≥0.1 GeV gamma-ray pulsar detections using three years of data acquired by the Large Area Telescope (LAT) on the Fermi satellite. Half are neutron stars discovered using LAT data through periodicity searches in gamma-ray and radio data around LAT unassociated source positions. The 117 pulsars are evenly divided into three groups: millisecond pulsars, young radio-loud pulsars, and young radio-quiet pulsars. We characterize the pulse profiles and energy spectra and derive luminosities when distance information exists. Spectral analysis of the off-peak phase intervals indicates probable pulsar wind nebula emission for four pulsars, and off-peak magnetospheric emission for several young and millisecond pulsars. We compare the gamma-ray properties with those in the radio, optical, and X-ray bands. We provide flux limits for pulsars with no observed gamma-ray emission, highlighting a small number of gamma-faint, radio-loud pulsars. The large, varied gamma-ray pulsar sample constrains emission models. Fermi's selection biases complement those of radio surveys, enhancing comparisons with predicted population distributions.

The second FERMI large area telescope catalog of gamma-ray pulsars

Energy Technology Data Exchange (ETDEWEB)

Abdo, A. A.; Ajello, M.; Allafort, A.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Belfiore, A.; Bellazzini, R.; Bhattacharyya, B.; Bissaldi, E.; Bloom, E. D.; Bonamente, E.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Burgay, M.; Burnett, T. H.; Busetto, G.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Camilo, F.; Caraveo, P. A.; Casandjian, J. M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chaty, S.; Chaves, R. C. G.; Chekhtman, A.; Chen, A. W.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cognard, I.; Cohen-Tanugi, J.; Cominsky, L. R.; Conrad, J.; Cutini, S.; D' Ammando, F.; de Angelis, A.; DeCesar, M. E.; De Luca, A.; den Hartog, P. R.; de Palma, F.; Dermer, C. D.; Desvignes, G.; Digel, S. W.; Di Venere, L.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Dumora, D.; Espinoza, C. M.; Falletti, L.; Favuzzi, C.; Ferrara, E. C.; Focke, W. B.; Franckowiak, A.; Freire, P. C. C.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Gotthelf, E. V.; Grenier, I. A.; Grondin, M. -H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Hessels, J.; Hewitt, J.; Hill, A. B.; Horan, D.; Hou, X.; Hughes, R. E.; Jackson, M. S.; Janssen, G. H.; Jogler, T.; Jóhannesson, G.; Johnson, R. P.; Johnson, A. S.; Johnson, T. J.; Johnson, W. N.; Johnston, S.; Kamae, T.; Kataoka, J.; Keith, M.; Kerr, M.; Knödlseder, J.; Kramer, M.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Lyne, A. G.; Manchester, R. N.; Marelli, M.; Massaro, F.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; McLaughlin, M. A.; Mehault, J.; Michelson, P. F.; Mignani, R. P.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Nemmen, R.; Nuss, E.; Ohno, M.; Ohsugi, T.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Parent, D.; Perkins, J. S.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Pletsch, H. J.; Porter, T. A.; Possenti, A.; Rainò, S.; Rando, R.; Ransom, S. M.; Ray, P. S.; Razzano, M.; Rea, N.; Reimer, A.; Reimer, O.; Renault, N.; Reposeur, T.; Ritz, S.; Romani, R. W.; Roth, M.; Rousseau, R.; Roy, J.; Ruan, J.; Sartori, A.; Saz Parkinson, P. M.; Scargle, J. D.; Schulz, A.; Sgrò, C.; Shannon, R.; Siskind, E. J.; Smith, D. A.; Spandre, G.; Spinelli, P.; Stappers, B. W.; Strong, A. W.; Suson, D. J.; Takahashi, H.; Thayer, J. G.; Thayer, J. B.; Theureau, G.; Thompson, D. J.; Thorsett, S. E.; Tibaldo, L.; Tibolla, O.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Venter, C.; Vianello, G.; Vitale, V.; Wang, N.; Weltevrede, P.; Winer, B. L.; Wolff, M. T.; Wood, D. L.; Wood, K. S.; Wood, M.; Yang, Z.

2013-09-19

This catalog summarizes 117 high-confidence ≥0.1 GeV gamma-ray pulsar detections using three years of data acquired by the Large Area Telescope (LAT) on the Fermi satellite. Half are neutron stars discovered using LAT data through periodicity searches in gamma-ray and radio data around LAT unassociated source positions. The 117 pulsars are evenly divided into three groups: millisecond pulsars, young radio-loud pulsars, and young radio-quiet pulsars. We characterize the pulse profiles and energy spectra and derive luminosities when distance information exists. Spectral analysis of the off-peak phase intervals indicates probable pulsar wind nebula emission for four pulsars, and off-peak magnetospheric emission for several young and millisecond pulsars. We compare the gamma-ray properties with those in the radio, optical, and X-ray bands. We provide flux limits for pulsars with no observed gamma-ray emission, highlighting a small number of gamma-faint, radio-loud pulsars. The large, varied gamma-ray pulsar sample constrains emission models. Fermi's selection biases complement those of radio surveys, enhancing comparisons with predicted population distributions.

The second fermi large area telescope catalog of gamma-ray pulsars

Energy Technology Data Exchange (ETDEWEB)

Abdo, A. A.; Ajello, M.; Allafort, A.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Belfiore, A.; Bellazzini, R.; Bhattacharyya, B.; Bissaldi, E.; Bloom, E. D.; Bonamente, E.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Burgay, M.; Burnett, T. H.; Busetto, G.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Camilo, F.; Caraveo, P. A.; Casandjian, J. M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chaty, S.; Chaves, R. C. G.; Chekhtman, A.; Chen, A. W.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cognard, I.; Cohen-Tanugi, J.; Cominsky, L. R.; Conrad, J.; Cutini, S.; D' Ammando, F.; de Angelis, A.; DeCesar, M. E.; De Luca, A.; den Hartog, P. R.; de Palma, F.; Dermer, C. D.; Desvignes, G.; Digel, S. W.; Di Venere, L.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Dumora, D.; Espinoza, C. M.; Falletti, L.; Favuzzi, C.; Ferrara, E. C.; Focke, W. B.; Franckowiak, A.; Freire, P. C. C.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Gotthelf, E. V.; Grenier, I. A.; Grondin, M. -H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Hessels, J.; Hewitt, J.; Hill, A. B.; Horan, D.; Hou, X.; Hughes, R. E.; Jackson, M. S.; Janssen, G. H.; Jogler, T.; Jóhannesson, G.; Johnson, R. P.; Johnson, A. S.; Johnson, T. J.; Johnson, W. N.; Johnston, S.; Kamae, T.; Kataoka, J.; Keith, M.; Kerr, M.; Knödlseder, J.; Kramer, M.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Lyne, A. G.; Manchester, R. N.; Marelli, M.; Massaro, F.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; McLaughlin, M. A.; Mehault, J.; Michelson, P. F.; Mignani, R. P.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Nemmen, R.; Nuss, E.; Ohno, M.; Ohsugi, T.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Parent, D.; Perkins, J. S.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Pletsch, H. J.; Porter, T. A.; Possenti, A.; Rainò, S.; Rando, R.; Ransom, S. M.; Ray, P. S.; Razzano, M.; Rea, N.; Reimer, A.; Reimer, O.; Renault, N.; Reposeur, T.; Ritz, S.; Romani, R. W.; Roth, M.; Rousseau, R.; Roy, J.; Ruan, J.; Sartori, A.; Saz Parkinson, P. M.; Scargle, J. D.; Schulz, A.; Sgrò, C.; Shannon, R.; Siskind, E. J.; Smith, D. A.; Spandre, G.; Spinelli, P.; Stappers, B. W.; Strong, A. W.; Suson, D. J.; Takahashi, H.; Thayer, J. G.; Thayer, J. B.; Theureau, G.; Thompson, D. J.; Thorsett, S. E.; Tibaldo, L.; Tibolla, O.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Venter, C.; Vianello, G.; Vitale, V.; Wang, N.; Weltevrede, P.; Winer, B. L.; Wolff, M. T.; Wood, D. L.; Wood, K. S.; Wood, M.; Yang, Z.

2013-09-19

This catalog summarizes 117 high-confidence ≥0.1 GeV gamma-ray pulsar detections using three years of data acquired by the Large Area Telescope (LAT) on the Fermi satellite. Half are neutron stars discovered using LAT data through periodicity searches in gamma-ray and radio data around LAT unassociated source positions. The 117 pulsars are evenly divided into three groups: millisecond pulsars, young radio-loud pulsars, and young radio-quiet pulsars. We characterize the pulse profiles and energy spectra and derive luminosities when distance information exists. Spectral analysis of the off-peak phase intervals indicates probable pulsar wind nebula emission for four pulsars, and off-peak magnetospheric emission for several young and millisecond pulsars. We compare the gamma-ray properties with those in the radio, optical, and X-ray bands. We provide flux limits for pulsars with no observed gamma-ray emission, highlighting a small number of gamma-faint, radio-loud pulsars. The large, varied gamma-ray pulsar sample constrains emission models. Fermi's selection biases complement those of radio surveys, enhancing comparisons with predicted population distributions.

Relaxation of ion energy spectrum just after turbulent heating pulse in TRIAM-1 tokamak

International Nuclear Information System (INIS)

Nakamura, Kazuo; Hiraki, Naoji; Nakamura, Yukio; Itoh, Satoshi

1982-01-01

The temporal evolution and spatial profile of the ion energy spectrum just after the application of a toroidal current pulse for turbulent heating are investigated experimentally in the TRIAM-1 tokamak and also numerically using the Fokker-Planck equation. The two-component ion energy spectrum formed by turbulent heating relaxes to a single one within tausub(i) (the ion collision time). (author)

Relaxation of ion energy spectrum just after turbulent heating pulse in TRIAM-1 tokamak

Energy Technology Data Exchange (ETDEWEB)

Nakamura, Kazuo; Hiraki, Naoji; Nakamura, Yukio; Itoh, Satoshi [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics

1982-07-01

The temporal evolution and spatial profile of the ion energy spectrum just after the application of a toroidal current pulse for turbulent heating are investigated experimentally in the TRIAM-1 tokamak and also numerically using the Fokker-Planck equation. The two-component ion energy spectrum formed by turbulent heating relaxes to a single one within tausub(i) (the ion collision time).

X-RAY OBSERVATIONS OF THE YOUNG PULSAR J1357—6429 AND ITS PULSAR WIND NEBULA

International Nuclear Information System (INIS)

Chang, Chulhoon; Pavlov, George G.; Kargaltsev, Oleg; Shibanov, Yurii A.

2012-01-01

We observed the young pulsar J1357—6429 with the Chandra and XMM-Newton observatories. The pulsar spectrum fits well a combination of an absorbed power-law model (Γ = 1.7 ± 0.6) and a blackbody model (kT = 140 +60 –40 eV, R ∼ 2 km at the distance of 2.5 kpc). Strong pulsations with pulsed fraction of 42% ± 5%, apparently associated with the thermal component, were detected in 0.3-1.1 keV. Surprisingly, the pulsed fraction at higher energies, 1.1-10 keV, appears to be smaller, 23% ± 4%. The small emitting area of the thermal component either corresponds to a hotter fraction of the neutron star surface or indicates inapplicability of the simplistic blackbody description. The X-ray images also reveal a pulsar wind nebula (PWN) with complex, asymmetric morphology comprised of a brighter, compact PWN surrounded by the fainter, much more extended PWN whose spectral slopes are Γ = 1.3 ± 0.3 and Γ = 1.7 ± 0.2, respectively. The extended PWN with the observed flux of ∼7.5 × 10 –13 erg s –1 cm –2 is a factor of 10 more luminous then the compact PWN. The pulsar and its PWN are located close to the center of the extended TeV source HESS J1356-645, which strongly suggests that the very high energy emission is powered by electrons injected by the pulsar long ago. The X-ray to TeV flux ratio, ∼0.1, is similar to those of other relic PWNe. We found no other viable candidates to power the TeV source. A region of diffuse radio emission, offset from the pulsar toward the center of the TeV source, could be synchrotron emission from the same relic PWN rather than from the supernova remnant.

Coherent amplification and pulsar phenomena

International Nuclear Information System (INIS)

Casperson, L.W.

1977-01-01

A modification of the rotating-star model has been developed to interpret the periodic energy bursts from pulsars. This new configuration involves theta-directed oscillation modes in the stellar atmosphere or magnetosphere, and most aspects of the typical pulse characteristics are well accounted for. Gain is provided by resonant interactions with particles trapped in the stellar magnetic field. The most significant feature is the fact that highly directional beaming of the output energy results as a natural consequence of coherence between the radiation fields emerging from various locations about the pulsar; and a localized radiation origin is not required. (Auth.)

PULSED GAMMA RAYS FROM THE MILLISECOND PULSAR J0030+0451 WITH THE FERMI LARGE AREA TELESCOPE

International Nuclear Information System (INIS)

Abdo, A. A.; Ackermann, M.; Bechtol, K.; Berenji, B.; Bloom, E. D.; Borgland, A. W.; Atwood, W. B.; Axelsson, M.; Battelino, M.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B. M.; Bonamente, E.; Brigida, M.; Bruel, P.

2009-01-01

We report the discovery of gamma-ray pulsations from the nearby isolated millisecond pulsar (MSP) PSR J0030+0451 with the Large Area Telescope on the Fermi Gamma-ray Space Telescope (formerly GLAST). This discovery makes PSR J0030+0451 the second MSP to be detected in gamma rays after PSR J0218+4232, observed by the EGRET instrument on the Compton Gamma-Ray Observatory. The spin-down power E-dot=3.5x10 33 erg s -1 is an order of magnitude lower than the empirical lower bound of previously known gamma-ray pulsars. The emission profile is characterized by two narrow peaks, 0.07 ± 0.01 and 0.08 ± 0.02 wide, respectively, separated by 0.44 ± 0.02 in phase. The first gamma-ray peak falls 0.15 ± 0.01 after the main radio peak. The pulse shape is similar to that of the 'normal' gamma-ray pulsars. An exponentially cutoff power-law fit of the emission spectrum leads to an integral photon flux above 100 MeV of (6.76 ± 1.05 ± 1.35) x 10 -8 cm -2 s -1 with cutoff energy (1.7 ± 0.4 ± 0.5) GeV. Based on its parallax distance of (300 ± 90) pc, we obtain a gamma-ray efficiency L γ /E-dot≅15 percent for the conversion of spin-down energy rate into gamma-ray radiation, assuming isotropic emission.

POLARIZATION OBSERVATIONS OF 100 PULSARS AT 774 MHz BY THE GREEN BANK TELESCOPE

International Nuclear Information System (INIS)

Han, J. L.; Demorest, P. B.; Van Straten, W.; Lyne, A. G.

2009-01-01

We report on polarimetric observations of 100 pulsars centered on 774 MHz, made using the Green Bank Telescope, presenting their polarization profiles and polarized flux densities and comparing them with previous observations when possible. For 67 pulsars, these are the first such measurements made. Polarization profiles of 8 millisecond-pulsars in our sample show wide profiles and flat position-angle curves. Strong linear polarization, sometimes approaching 100% of the total intensity, has been detected in all or a part of the average pulse profiles of some pulsars. In general, circular polarization is very weak, although it is observed to be extremely strong in the leading component of PSR J1920+2650. Sense reversal of circular polarization as a function of pulse phase has been detected from both core and other components of more than 20 pulsars. Any relationship between the spin-down luminosity and the percentage of linear polarization is not evident in our data at this frequency.

Discovery of a 50 millisecond pulsar in the Large Magellanic Cloud

Science.gov (United States)

Seward, F. D.; Harnden, F. R., Jr.; Helfand, D. J.

1984-01-01

The present investigation is concerned with the discovery of a new pulsed X-ray source in the Large Magellanic Cloud (LMC) supernova remnant 0540 - 693. The SNR 0540 - 693 is one of three suspected Crab-like remnants in the LMC. The existing X-ray, optical, and radio observations of the remnant itself are discussed, and an analysis is conducted of the implications of the period, period derivative, and X-ray pulse shape of the new source. It is concluded that the pulsed X-ray source is almost certainly a young, isolated pulsar. Many of its properties are very similar to those of the Crab pulsar.

Radio Detection of the Fermi-LAT Blind Search Millisecond Pulsar J1311-3430

Science.gov (United States)

Ray, P. S.; Ransom, S. M.; Cheung, C. C.; Giroletti, M.; Cognard, I.; Camilo, F.; Bhattacharyya, B.; Roy, J.; Romani, R. W.; Ferrara, E. C.; Guillemot, L.; Johnston, S.; Keith, M.; Kerr, M.; Kramer, M.; Pletsch, H. J.; Saz Parkinson, P. M.; Wood, K. S.

2013-01-01

We report the detection of radio emission from PSR J1311-3430, the first millisecond pulsar (MSP) discovered in a blind search of Fermi Large Area Telescope (LAT) gamma-ray data. We detected radio pulsations at 2 GHz, visible for delay in the radio pulses as the pulsar appears from eclipse and we speculate on possible mechanisms for the non-detections of the pulse at other orbital phases and observing frequencies.

The Einstein@Home Gamma-ray Pulsar Survey. II. Source Selection, Spectral Analysis, and Multiwavelength Follow-up

Science.gov (United States)

Wu, J.; Clark, C. J.; Pletsch, H. J.; Guillemot, L.; Johnson, T. J.; Torne, P.; Champion, D. J.; Deneva, J.; Ray, P. S.; Salvetti, D.; Kramer, M.; Aulbert, C.; Beer, C.; Bhattacharyya, B.; Bock, O.; Camilo, F.; Cognard, I.; Cuéllar, A.; Eggenstein, H. B.; Fehrmann, H.; Ferrara, E. C.; Kerr, M.; Machenschalk, B.; Ransom, S. M.; Sanpa-Arsa, S.; Wood, K.

2018-02-01

We report on the analysis of 13 gamma-ray pulsars discovered in the Einstein@Home blind search survey using Fermi Large Area Telescope (LAT) Pass 8 data. The 13 new gamma-ray pulsars were discovered by searching 118 unassociated LAT sources from the third LAT source catalog (3FGL), selected using the Gaussian Mixture Model machine-learning algorithm on the basis of their gamma-ray emission properties being suggestive of pulsar magnetospheric emission. The new gamma-ray pulsars have pulse profiles and spectral properties similar to those of previously detected young gamma-ray pulsars. Follow-up radio observations have revealed faint radio pulsations from two of the newly discovered pulsars and enabled us to derive upper limits on the radio emission from the others, demonstrating that they are likely radio-quiet gamma-ray pulsars. We also present results from modeling the gamma-ray pulse profiles and radio profiles, if available, using different geometric emission models of pulsars. The high discovery rate of this survey, despite the increasing difficulty of blind pulsar searches in gamma rays, suggests that new systematic surveys such as presented in this article should be continued when new LAT source catalogs become available.

Physical conditions in the reconnection layer in pulsar magnetospheres

Energy Technology Data Exchange (ETDEWEB)

Uzdensky, Dmitri A. [Center for Integrated Plasma Studies, Physics Department, University of Colorado, UCB 390, Boulder, CO 80309-0390 (United States); Spitkovsky, Anatoly, E-mail: uzdensky@colorado.edu, E-mail: anatoly@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2014-01-01

The magnetosphere of a rotating pulsar naturally develops a current sheet (CS) beyond the light cylinder (LC). Magnetic reconnection in this CS inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. We develop a basic physical picture of reconnection in this environment and discuss its implications for the observed pulsed gamma-ray emission. We argue that reconnection proceeds in the plasmoid-dominated regime, via a hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. Using the conditions of pressure balance across these current layers, the balance between the heating by magnetic energy dissipation and synchrotron cooling, and Ampere's law, we obtain simple estimates for key parameters of the layers—temperature, density, and layer thickness. In the comoving frame of the relativistic pulsar wind just outside of the equatorial CS, these basic parameters are uniquely determined by the strength of the reconnecting upstream magnetic field. For the case of the Crab pulsar, we find them to be of order 10 GeV, 10{sup 13} cm{sup –3}, and 10 cm, respectively. After accounting for the bulk Doppler boosting due to the pulsar wind, the synchrotron and inverse-Compton emission from the reconnecting CS can explain the observed pulsed high-energy (GeV) and very high energy (∼100 GeV) radiation, respectively. Also, we suggest that the rapid relative motions of the secondary plasmoids in the hierarchical chain may contribute to the production of the pulsar radio emission.

WIDE-BAND SPECTRA OF GIANT RADIO PULSES FROM THE CRAB PULSAR

Energy Technology Data Exchange (ETDEWEB)

Mikami, Ryo; Asano, Katsuaki [Institute for Cosmic Ray Research, The University of Tokyo, Kashiwa, Chiba 277-8582 (Japan); Tanaka, Shuta J. [Department of Physics, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Kobe, Hyogo, 658-8501 (Japan); Kisaka, Shota [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa, 252-5258 (Japan); Sekido, Mamoru; Takefuji, Kazuhiro [Kashima Space Technology Center, National Institute of Information and Communications Technology, Kashima, Ibaraki 314-8501 (Japan); Takeuchi, Hiroshi [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210 (Japan); Misawa, Hiroaki; Tsuchiya, Fuminori [Planetary Plasma and Atmospheric Research Center, Tohoku University, Sendai, Miyagi 980-8578 (Japan); Kita, Hajime [Department of Geophysics, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578 (Japan); Yonekura, Yoshinori [Center for Astronomy, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan); Terasawa, Toshio, E-mail: mikami@icrr.u-tokyo.ac.jp, E-mail: asanok@icrr.u-tokyo.ac.jp [iTHES Research Group, RIKEN, Wako, Saitama 351-0198 (Japan)

2016-12-01

We present the results of the simultaneous observation of giant radio pulses (GRPs) from the Crab pulsar at 0.3, 1.6, 2.2, 6.7, and 8.4 GHz with four telescopes in Japan. We obtain 3194 and 272 GRPs occurring at the main pulse and the interpulse phases, respectively. A few GRPs detected at both 0.3 and 8.4 GHz are the most wide-band samples ever reported. In the frequency range from 0.3 to 2.2 GHz, we find that about 70% or more of the GRP spectra are consistent with single power laws and their spectral indices are distributed from −4 to −1. We also find that a significant number of GRPs have such a hard spectral index (approximately −1) that the fluence at 0.3 GHz is below the detection limit (“dim-hard” GRPs). Stacking light curves of such dim-hard GRPs at 0.3 GHz, we detect consistent enhancement compared to the off-GRP light curve. Our samples show apparent correlations between the fluences and the spectral hardness, which indicates that more energetic GRPs tend to show softer spectra. Our comprehensive studies on the GRP spectra are useful materials to verify the GRP model of fast radio bursts in future observations.

WIDE-BAND SPECTRA OF GIANT RADIO PULSES FROM THE CRAB PULSAR

International Nuclear Information System (INIS)

Mikami, Ryo; Asano, Katsuaki; Tanaka, Shuta J.; Kisaka, Shota; Sekido, Mamoru; Takefuji, Kazuhiro; Takeuchi, Hiroshi; Misawa, Hiroaki; Tsuchiya, Fuminori; Kita, Hajime; Yonekura, Yoshinori; Terasawa, Toshio

2016-01-01

We present the results of the simultaneous observation of giant radio pulses (GRPs) from the Crab pulsar at 0.3, 1.6, 2.2, 6.7, and 8.4 GHz with four telescopes in Japan. We obtain 3194 and 272 GRPs occurring at the main pulse and the interpulse phases, respectively. A few GRPs detected at both 0.3 and 8.4 GHz are the most wide-band samples ever reported. In the frequency range from 0.3 to 2.2 GHz, we find that about 70% or more of the GRP spectra are consistent with single power laws and their spectral indices are distributed from −4 to −1. We also find that a significant number of GRPs have such a hard spectral index (approximately −1) that the fluence at 0.3 GHz is below the detection limit (“dim-hard” GRPs). Stacking light curves of such dim-hard GRPs at 0.3 GHz, we detect consistent enhancement compared to the off-GRP light curve. Our samples show apparent correlations between the fluences and the spectral hardness, which indicates that more energetic GRPs tend to show softer spectra. Our comprehensive studies on the GRP spectra are useful materials to verify the GRP model of fast radio bursts in future observations.

A Physical Model of Pulsars as Gravitational Shielding and Oscillating Neutron Stars

Directory of Open Access Journals (Sweden)

Zhang T. X.

2015-04-01

Full Text Available Pulsars are thought to be fast rotating neutron stars, synchronously emitting periodic Dirac-delta-shape radio-frequency pulses and Lorentzian-shape oscillating X-rays. The acceleration of charged particles along the magnetic field lines of neutron stars above the magnetic poles that deviate from the rotating axis initiates coherent beams of ra- dio emissions, which are viewed as pulses of radiation whenever the magnetic poles sweep the viewers. However, the conventional lighthouse model of pulsars is only con- ceptual. The mechanism through which particles are accelerated to produce coherent beams is still not fully understood. The process for periodically oscillating X-rays to emit from hot spots at the inner edge of accretion disks remains a mystery. In addition, a lack of reflecting X-rays of the pulsar by the Crab Nebula in the OFF phase does not support the lighthouse model as expected. In this study, we develop a physical model of pulsars to quantitatively interpret the emission characteristics of pulsars, in accor- dance with the author’s well-developed five-dimensional fully covariant Kaluza-Klein gravitational shielding theory and the physics of thermal and accelerating charged par- ticle radiation. The results obtained from this study indicate that, with the significant gravitational shielding by scalar field, a neutron star nonlinearly oscillates and produces synchronous periodically Dirac-delta-shape radio-frequency pulses (emitted by the os- cillating or accelerating charged particles as well as periodically Lorentzian-shape os- cillating X-rays (as the thermal radiation of neutron stars whose temperature varies due to the oscillation. This physical model of pulsars broadens our understanding of neu- tron stars and develops an innovative mechanism to model the emissions of pulsars.

Geriatric Pulsar Still Kicking

Science.gov (United States)

2009-02-01

The oldest isolated pulsar ever detected in X-rays has been found with NASA's Chandra X-ray Observatory. This very old and exotic object turns out to be surprisingly active. The pulsar, PSR J0108-1431 (J0108 for short) is about 200 million years old. Among isolated pulsars -- ones that have not been spun-up in a binary system -- it is over 10 times older than the previous record holder with an X-ray detection. At a distance of 770 light years, it is one of the nearest pulsars known. Pulsars are born when stars that are much more massive than the Sun collapse in supernova explosions, leaving behind a small, incredibly weighty core, known as a neutron star. At birth, these neutron stars, which contain the densest material known in the Universe, are spinning rapidly, up to a hundred revolutions per second. As the rotating beams of their radiation are seen as pulses by distant observers, similar to a lighthouse beam, astronomers call them "pulsars". Astronomers observe a gradual slowing of the rotation of the pulsars as they radiate energy away. Radio observations of J0108 show it to be one of the oldest and faintest pulsars known, spinning only slightly faster than one revolution per second. The surprise came when a team of astronomers led by George Pavlov of Penn State University observed J0108 in X-rays with Chandra. They found that it glows much brighter in X-rays than was expected for a pulsar of such advanced years. People Who Read This Also Read... Chandra Data Reveal Rapidly Whirling Black Holes Milky Way’s Giant Black Hole Awoke from Slumber 300 Years Ago Erratic Black Hole Regulates Itself Celebrate the International Year of Astronomy Some of the energy that J0108 is losing as it spins more slowly is converted into X-ray radiation. The efficiency of this process for J0108 is found to be higher than for any other known pulsar. "This pulsar is pumping out high-energy radiation much more efficiently than its younger cousins," said Pavlov. "So, although it

Optical pulsar in the Large Magellanic Cloud remnant 0540-69.3

International Nuclear Information System (INIS)

Middleditch, J.; Pennypacker, C.R.

1984-01-01

We have detected pulsed optical emission from the Large Magellanic Cloud (LMC) X-ray pulsar PSR 0540-693 (Seward et al. 1984). The pulsed emission has a time averaged magnitude of approximately 22.7. The X-ray pulsar was discovered in the LMC remnant, 0540-69.3 as a pulse repetition period of approx. 50 milliseconds (ms) in Einstein Obsrvatory data (Seward et al. 1984). Earlier, Clark et al. (1982) had noted that this remnant resembles the Crab Nebula because of the X-ray power law spectrum, and suggested that the nebular emission was synchrotron radiation powered by a central pulsar. After the announcement of X-ray pulsed emission, Chanan et al. (1984) measured the broad optical band properties of the nebula and found evidence for synchrotron emission. They reported that the 4.5 arc second continuum emission remnant has only a tenth the luminosity of the Crab Nebula. We have recorded broad-band optical time-series data at 1 ms intervals with the 4-m and 1.5-m Cerro Tololo telescopes and have found strong pulsations, employing the usual Fourier transform methods. A summary of the observations, including magnitudes, barycentric frequencies and times of arrival is given

High-Energy Emission from Rotation-Powered Pulsars

Science.gov (United States)

Harding, Alice K.

2007-01-01

Thirty-five years after the discovery of rotation-powered pulsars, we still do not understand their pulsed emission at any wavelength. In the last few years there have been some fundamental developments in acceleration and emission models. I will review both the basic physics of the models as well as the latest developments in understanding the high-energy emission of rotation-powered pulsars. Special and general relativistic effects play important roles in pulsar emission, from inertial frame-dragging near the stellar surface to aberration, time-of-flight and retardation of the magnetic field near the light cylinder. Understanding how these effects determine what we observe at different wavelengths is critical to unraveling the emission physics. Fortunately two new gamma-ray telescopes, AGILE and GLAST, with launches expected this year will detect many new gamma-ray pulsars and test the predictions of these models with unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 300 GeV.

Soft excess and orbital evolution studies of X-ray pulsars with BeppoSAX

International Nuclear Information System (INIS)

Paul, B.; Naik, S.; Bhatt, N.

2004-01-01

We present here a spectral study of two accreting binary X-ray pulsars LMC X-4 and SMC X-1 made with the BeppoSAX observatory. The energy spectrum of both the pulsars in 0.1-10.0 keV band can be described by a model consisting of a hard power-law component, a soft excess and an iron emission line at 6.4 keV. In addition, the power-law component of SMC X-1 also has an exponential cutoff at ∼ 6 keV. Pulse-phase resolved spectroscopy confirms a pulsating nature of the soft spectral component in both the pulsars, with a certain phase offset compared to the hard power-law component. A dissimilar pulse profile of the two spectral components and a phase difference between the pulsating soft and hard spectral components are evidence for their different origins. In another study of an accreting binary X-ray pulsar Her X-1, we have made accurate measurements of new mid-eclipse times from pulse arrival time delays using observations made with the BeppoSAX and RXTE observatories. The new measurements, combined with the earlier reported mid-eclipse times are used to investigate orbital evolution of the binary. The most recent observation indicates deviation from a quadratic trend coincident with an anomalous low X-ray state, observed for the second time in this pulsar

Pulsed Thermal Emission from the Accreting Pulsar XMMU J054134.7-682550

Science.gov (United States)

Manousakis, Antonis; Walter, Roland; Audard, Marc; Lanz, Thierry

2009-05-01

XMMU J054134.7-682550, located in the LMC, featured a type II outburst in August 2007. We analyzed XMM-Newton (EPIC-MOS) and RXTE (PCA) data in order to derive the spectral and temporal characteristics of the system throughout the outburst. Spectral variability, spin period evolution, energy dependent pulse shape are discussed. The outburst (LX~3×1038 erg/s~LEDD) spectrum can be modeled using, cutoff power law, soft X-ray blackbody, disk emission, and cyclotron absorption line. The blackbody component shows a sinusoidal behavior, expected from hard X-ray reprocessing on the inner edge of the accretion disk. The thickness of the inner accretion disk (width of ~75 km) can be constrained. The spin-up of the pulsar during the outburst is the signature of a (huge) accretion rate. Simbol-X will provide similar capabilities as XMM-Newton and RXTE together, for such bright events.

Resolving discrete pulsar spin-down states with current and future instrumentation

Science.gov (United States)

Shaw, B.; Stappers, B. W.; Weltevrede, P.

2018-04-01

An understanding of pulsar timing noise offers the potential to improve the timing precision of a large number of pulsars as well as facilitating our understanding of pulsar magnetospheres. For some sources, timing noise is attributable to a pulsar switching between two different spin-down rates (\\dot{ν }). Such transitions may be common but difficult to resolve using current techniques. In this work, we use simulations of \\dot{ν }-variable pulsars to investigate the likelihood of resolving individual \\dot{ν } transitions. We inject step changes in the value of \\dot{ν } with a wide range of amplitudes and switching time-scales. We then attempt to redetect these transitions using standard pulsar timing techniques. The pulse arrival-time precision and the observing cadence are varied. Limits on \\dot{ν } detectability based on the effects such transitions have on the timing residuals are derived. With the typical cadences and timing precision of current timing programmes, we find that we are insensitive to a large region of Δ \\dot{ν } parameter space that encompasses small, short time-scale switches. We find, where the rotation and emission states are correlated, that using changes to the pulse shape to estimate \\dot{ν } transition epochs can improve detectability in certain scenarios. The effects of cadence on Δ \\dot{ν } detectability are discussed, and we make comparisons with a known population of intermittent and mode-switching pulsars. We conclude that for short time-scale, small switches, cadence should not be compromised when new generations of ultra-sensitive radio telescopes are online.

Detecting stochastic backgrounds of gravitational waves with pulsar timing arrays

Science.gov (United States)

Siemens, Xavier

2016-03-01

For the past decade the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the Green Bank Telescope and the Arecibo Observatory to monitor millisecond pulsars. NANOGrav, along with two other international collaborations, the European Pulsar Timing Array and the Parkes Pulsar Timing Array in Australia, form a consortium of consortia: the International Pulsar Timing Array (IPTA). The goal of the IPTA is to directly detect low-frequency gravitational waves which cause small changes to the times of arrival of radio pulses from millisecond pulsars. In this talk I will discuss the work of NANOGrav and the IPTA, as well as our sensitivity to stochastic backgrounds of gravitational waves. I will show that a detection of the background produced by supermassive black hole binaries is possible by the end of the decade. Supported by the NANOGrav Physics Frontiers Center.

THE GALACTIC POPULATION OF YOUNG γ-RAY PULSARS

International Nuclear Information System (INIS)

Watters, Kyle P.; Romani, Roger W.

2011-01-01

We have simulated a Galactic population of young pulsars and compared with the Fermi LAT sample, constraining the birth properties, beaming and evolution of these spin-powered objects. Using quantitative tests of agreement with the distributions of observed spin and pulse properties, we find that short birth periods P 0 ∼ 50 ms and γ-ray beams arising in the outer magnetosphere, dominated by a single pole, are strongly preferred. The modeled relative numbers of radio-detected and radio-quiet objects agrees well with the data. Although the sample is local, extrapolation to the full Galaxy implies a γ-ray pulsar birthrate 1/(59 yr). This is shown to be in good agreement with the estimated Galactic core collapse rate and with the local density of OB star progenitors. We give predictions for the numbers of expected young pulsar detections if Fermi LAT observations continue 10 years. In contrast to the potentially significant contribution of unresolved millisecond pulsars, we find that young pulsars should contribute little to the Galactic γ-ray background.

Localizing New Pulsars with Intensity Mapping

Science.gov (United States)

Swiggum, Joe; Gentile, Peter

2018-01-01

Although low-frequency, single dish pulsar surveys provide an efficient means of searching large regions of sky quickly, the localization of new discoveries is poor. For example, discoveries from 350 MHz surveys using the Green Bank Telescope (GBT) have position uncertainties up to the FWHM of the telescope's "beam" on the sky, over half a degree! Before finding a coherent timing solution (requires 8-12 months of dedicated timing observations) a "gridding" method is usually employed to improve localization of new pulsars, whereby a grid of higher frequency beam positions is used to tile the initial error region. This method often requires over an hour of observing time to achieve arcminute-precision localization (provided the pulsar is detectable at higher frequencies).Here, we describe another method that uses the same observing frequency as the discovery observation and scans over Right Ascension and Declination directions around the nominal position. A Gaussian beam model is fit to folded pulse profile intensities as a function of time/position to provide improved localization. Using five test cases, we show that intensity mapping localization at 350 MHz with the GBT yields pulsar positions to 1 arcminute precision, facilitating high-frequency follow-up and higher significance detections for future pulsar timing. This method is also well suited to be directly implemented in future low-frequency drift scan pulsar surveys (e.g. with the Five hundred meter Aperture Spherical Telescope; FAST).

A 24 hr global campaign to assess precision timing of the millisecond pulsar J1713+0747

Energy Technology Data Exchange (ETDEWEB)

Dolch, T.; Lam, M. T.; Cordes, J.; Chatterjee, S. [Astronomy Department, Cornell University, Ithaca, NY 14853 (United States); Bassa, C.; Hessels, J. W. T.; Janssen, G.; Kondratiev, V. [ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo (Netherlands); Bhattacharyya, B.; Jordan, C.; Keith, M. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL (United Kingdom); Champion, D. J.; Karuppusamy, R.; Kramer, M.; Lazarus, P. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Cognard, I. [Laboratoire de Physique et Chimie de l' Environnement et de l' Espace, LPC2E UMR 6115 CNRS, F-45071 Orléans Cedex 02, and Station de radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, F-18330 Nançay (France); Crowter, K. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Demorest, P. B. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22901 (United States); Jenet, F. A. [Center for Advanced Radio Astronomy, University of Texas, Rio Grande Valley, Brownsville, TX 78520 (United States); Jones, G., E-mail: tdolch@astro.cornell.edu [Columbia Astrophysics Laboratory, Columbia University, NY 10027 (United States); and others

2014-10-10

The radio millisecond pulsar J1713+0747 is regarded as one of the highest-precision clocks in the sky and is regularly timed for the purpose of detecting gravitational waves. The International Pulsar Timing Array Collaboration undertook a 24 hr global observation of PSR J1713+0747 in an effort to better quantify sources of timing noise in this pulsar, particularly on intermediate (1-24 hr) timescales. We observed the pulsar continuously over 24 hr with the Arecibo, Effelsberg, GMRT, Green Bank, LOFAR, Lovell, Nançay, Parkes, and WSRT radio telescopes. The combined pulse times-of-arrival presented here provide an estimate of what sources of timing noise, excluding DM variations, would be present as compared to an idealized √N improvement in timing precision, where N is the number of pulses analyzed. In the case of this particular pulsar, we find that intrinsic pulse phase jitter dominates arrival time precision when the signal-to-noise ratio of single pulses exceeds unity, as measured using the eight telescopes that observed at L band/1.4 GHz. We present first results of specific phenomena probed on the unusually long timescale (for a single continuous observing session) of tens of hours, in particular interstellar scintillation, and discuss the degree to which scintillation and profile evolution affect precision timing. This paper presents the data set as a basis for future, deeper studies.

The SUrvey for Pulsars and Extragalactic Radio Bursts - I. Survey description and overview

Science.gov (United States)

Keane, E. F.; Barr, E. D.; Jameson, A.; Morello, V.; Caleb, M.; Bhandari, S.; Petroff, E.; Possenti, A.; Burgay, M.; Tiburzi, C.; Bailes, M.; Bhat, N. D. R.; Burke-Spolaor, S.; Eatough, R. P.; Flynn, C.; Jankowski, F.; Johnston, S.; Kramer, M.; Levin, L.; Ng, C.; van Straten, W.; Krishnan, V. Venkatraman

2018-01-01

We describe the Survey for Pulsars and Extragalactic Radio Bursts (SUPERB), an ongoing pulsar and fast transient survey using the Parkes radio telescope. SUPERB involves real-time acceleration searches for pulsars and single-pulse searches for pulsars and fast radio bursts. We report on the observational set-up, data analysis, multiwavelength/messenger connections, survey sensitivities to pulsars and fast radio bursts and the impact of radio frequency interference. We further report on the first 10 pulsars discovered in the project. Among these is PSR J1306-40, a millisecond pulsar in a binary system where it appears to be eclipsed for a large fraction of the orbit. PSR J1421-4407 is another binary millisecond pulsar; its orbital period is 30.7 d. This orbital period is in a range where only highly eccentric binaries are known, and expected by theory; despite this its orbit has an eccentricity of 10-5.

Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT

International Nuclear Information System (INIS)

Anderson, B.; Atwood, W.B.; Dormody, M.; Johnson, R.P.; Porter, T.A.; Primack, J.R.; Sadrozinski, H.F.W.; Parkinson, P.M.S.; Ziegler, M.; Abdo, A.A.; Dermer, C.D.; Grove, J.E.; Gwon, C.; Johnson, W.N.; Lovellette, M.N.; Makeev, A.; Ray, P.S.; Strickman, M.S.; Wolff, M.T.; Wood, K.S.; Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Blandford, R.D.; Borgland, A.W.; Cameron, R.A.; Chiang, J.; Claus, R.; Digel, S.W.; Silva, E.D.E.; Drell, P.S.; Dubois, R.; Funk, S.; Glanzman, T.; Godfrey, G.; Hayashida, M.; Johannesson, G.; Kamae, T.; Kocian, M.L.; Lande, J.; Madejski, G.M.; Michelson, P.F.; Mitthumsiri, W.; Monzani, M.E.; Moskalenko, I.V.; Murgia, S.; Nolan, P.L.; Paneque, D.; Reimer, A.; Reimer, O.; Rochester, L.S.; Romani, R.W.; Tajima, H.; Tanaka, T.; Thayer, J.G.; Tramacere, A.; Uchiyama, Y.; Usher, T.L.; Van Etten, A.; Waite, A.P.; Wang, P.; Watters, K.; Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Bloom, E.D.; Borgland, A.W.; Cameron, R.A.; Chiang, J.; Claus, R.; Digel, S.W.; Silva, E.D.E.; Drell, P.S.; Dubois, R.; Glanzman, T.; Godfrey, G.; Hayashida, M.; Johannesson, G.; Kamae, T.; Kocian, M.L.; Lande, J.; Madejski, G.M.; Michelson, P.F.; Mitthumsiri, W.; Monzani, M.E.; Moskalenko, I.V.; Murgia, S.; Nolan, P.L.; Paneque, D.; Reimer, A.; Reimer, O.; Rochester, L.S.; Romani, R.W.; Tajima, H.; Tanaka, T.; Thayer, J.G.; Tramacere, A.; Uchiyama, Y.; Usher, T.L.; Van Etten, A.; Waite, A.P.; Wang, P.; Watters, K.; Axelsson, M.; Conrad, J.; Meurer, C.; Ryde, F.; Ylinen, T.; Axelsson, M.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Kuss, M.; Latronico, L.; Omodei, N.; Pesce-Rollins, M.; Razzano, M.; Sgro, C.; Spandre, G.; Ballet, J.; Casandjian, J.M.; Grenier, I.A.; Pierbattista, M.; Starck, J.L.

2009-01-01

Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants. (authors)

SEXTANT X-Ray Pulsar Navigation Demonstration: Initial On-Orbit Results

Science.gov (United States)

Mitchell, Jason W.; Winternitz, Luke B.; Hassouneh, Munther A.; Price, Samuel R.; Semper, Sean R.; Yu, Wayne H.; Ray, Paul S.; Wolf, Michael T.; Kerr, Matthew; Wood, Kent S.;

Discovery of the Millisecond Pulsar PSR J2043+1711 in a Fermi Source with the Nancay Radio Telescope

Science.gov (United States)

Guillemot, L.; Freire, P. C. C.; Cognard, I.; Johnson, T. J.; Takahashi, Y.; Kataoka, J.; Desvignes, G.; Camilo, F.; Ferrara, E. C.; Harding, A. K.;

Small angle slot divertor concept for long pulse advanced tokamaks

Science.gov (United States)

Guo, H. Y.; Sang, C. F.; Stangeby, P. C.; Lao, L. L.; Taylor, T. S.; Thomas, D. M.

2017-04-01

SOLPS-EIRENE edge code analysis shows that a gas-tight slot divertor geometry with a small-angle (glancing-incidence) target, named the small angle slot (SAS) divertor, can achieve cold, dissipative/detached divertor conditions at relatively low values of plasma density at the outside midplane separatrix. SAS exhibits the following key features: (1) strong enhancement of the buildup of neutral density in a localized region near the plasma strike point on the divertor target; (2) spreading of the cooling front across the divertor target with the slot gradually flaring out from the strike point, thus effectively reducing both heat flux and erosion on the entire divertor target surface. Such a divertor may potentially provide a power and particle handling solution for long pulse advanced tokamaks.

X-Rays from the Nearby Solitary Millisecond Pulsar PSR J0030+0451 - the Final ROSAT Observations

CERN Document Server

Becker, W; Bäcker, A N; Lommen, D; Becker, Werner; Tr"umper, Joachim; Backer, Andrea N.Lommen & Donald C.

2000-01-01

We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+0451. The pulsar was one of the last targets observed in DEC-98 by the ROSAT PSPC. X-ray pulses are detected on a $4.5\\sigma$ level and make the source the $11^{th}$ millisecond pulsar detected in the X-ray domain. The pulsed fraction is found to be $69\\pm18%$. The X-ray pulse profile is characterized by two narrow peaks which match the gross pulse profile observed at 1.4 GHz. Assuming a Crab-like spectrum the X-ray flux is in the range $f_x= 2-3\\times 10^{-13}$ erg s$^{-1}$ cm$^{-2} $ ($0.1-2.4$ keV), implying an X-ray efficiency of $L_x/\\dot{E}\\sim 0.5-5 \\times 10^{-3} (d/0.23 {kpc})^2$.

A digital long pulse integrator

International Nuclear Information System (INIS)

Broesch, J.D.; Strait, E.J.; Snider, R.T.

1996-10-01

A prototype digital integrator with very long integration capabilities has been developed and field tested on an inductive magnetic sensor on the DIII-D Tokamak. The integrator is being developed for use on ITER with a pulse length of 1000 s, and has direct applications for other long pulse Tokamaks. Inductive magnetic sensors are routinely used on existing Tokamaks, are well understood, and are extremely robust, however, they require integration of the signal to determine the magnetic field strength. The next generation of Tokamaks, will have pulse lengths of 1000 s or longer, require integrators with drift and noise characteristics compatible with the very long pulse lengths. This paper will discuss the architecture, algorithms, and programming of the Long Pulse Integrator (LPI). Of particular interest are the noise control and the built-in offset correction techniques used in this application

DETECTING GRAVITATIONAL WAVE MEMORY WITH PULSAR TIMING

International Nuclear Information System (INIS)

Cordes, J. M.; Jenet, F. A.

2012-01-01

We compare the detectability of gravitational bursts passing through the solar system with those passing near each millisecond pulsar in an N-pulsar timing array. The sensitivity to Earth-passing bursts can exploit the correlation expected in pulse arrival times while pulsar-passing bursts, though uncorrelated between objects, provide an N-fold increase in overall time baseline that can compensate for the lower sensitivity. Bursts with memory from mergers of supermassive black holes produce step functions in apparent spin frequency that are the easiest to detect in pulsar timing. We show that the burst rate and amplitude distribution, while strongly dependent on inadequately known cosmological evolution, may favor detection in the pulsar terms rather than the Earth timing perturbations. Any contamination of timing data by red spin noise makes burst detection more difficult because both signals grow with the length of the time data span T. Furthermore, the different bursts that could appear in one or more data sets of length T ≈ 10 yr also affect the detectability of the gravitational wave stochastic background that, like spin noise, has a red power spectrum. A burst with memory is a worthwhile target in the timing of multiple pulsars in a globular cluster because it should produce a correlated signal with a time delay of less than about 10 years in some cases.

Detecting Gravitational Wave Memory with Pulsar Timing

Science.gov (United States)

Cordes, J. M.; Jenet, F. A.

2012-06-01

We compare the detectability of gravitational bursts passing through the solar system with those passing near each millisecond pulsar in an N-pulsar timing array. The sensitivity to Earth-passing bursts can exploit the correlation expected in pulse arrival times while pulsar-passing bursts, though uncorrelated between objects, provide an N-fold increase in overall time baseline that can compensate for the lower sensitivity. Bursts with memory from mergers of supermassive black holes produce step functions in apparent spin frequency that are the easiest to detect in pulsar timing. We show that the burst rate and amplitude distribution, while strongly dependent on inadequately known cosmological evolution, may favor detection in the pulsar terms rather than the Earth timing perturbations. Any contamination of timing data by red spin noise makes burst detection more difficult because both signals grow with the length of the time data span T. Furthermore, the different bursts that could appear in one or more data sets of length T ≈ 10 yr also affect the detectability of the gravitational wave stochastic background that, like spin noise, has a red power spectrum. A burst with memory is a worthwhile target in the timing of multiple pulsars in a globular cluster because it should produce a correlated signal with a time delay of less than about 10 years in some cases.

Space 'beachballs' generate pulsar bursts

CERN Multimedia

Wasowicz, L

2003-01-01

Researchers have analyzed radio emissions from a pulsar at the center of the Crab Nebula and have found 'subpulses' that last around 2 nanoseconds. They speculate this means the regions in which these ultra-short pulses are generated can be no larger than about 2 feet across - the distance light travels in 2 nanoseconds (2 pages).

A high-frequency survey of the southern Galactic plane for pulsars

Science.gov (United States)

Johnston, Simon; Lyne, A. G.; Manchester, R. N.; Kniffen, D. A.; D'Amico, N.; Lim, J.; Ashworth, M.

1992-01-01

Results of an HF survey designed to detect young, distant, and short-period pulsars are presented. The survey detected a total of 100 pulsars, 46 of which were previously unknown. The periods of the newly discovered pulsars range between 47 ms and 2.5 ms. One of the new discoveries, PSR 1259-63, is a member of a long-period binary system. At least three of the pulsars have ages less than 30,000 yr, bringing the total number of such pulsars to 12. The majority of the new discoveries are distant objects with high dispersion measures, which are difficult to detect at low frequencies. This demonstrates that the survey has reduced the severe selection effects of pulse scattering, high Galactic background temperature, and dispersion broadening, which hamper the detection of such pulsars at low radio frequencies. The pulsar distribution in the southern Galaxy is found to extend much further from the Galactic center than that in the north, probably due to two prominent spiral arms in the southern Galaxy.

X-ray Pulsars Across the Parameter Space of Luminosity, Accretion Mode, and Spin

Science.gov (United States)

Laycock, Silas

We propose to expand the scope of our successful project providing a multi-satellite library of X-ray Pulsar observations to the community. The library provides high-level products, activity monitoring, pulse-profiles, phased event files, spectra, and a unique pulse-profile modeling interface. The library's scientific footprint will expand in 4 key directions: (1) Update, by processing all new XMM-Newton and Chandra observations (2015-2017) of X-ray Binary Pulsars in the Magellanic Clouds. (2) Expand, by including all archival Suzaku, Swift and NuStar observations, and including Galactic pulsars. (3) Improve, by offering innovative data products that provide deeper insight. (4) Advance, by implementing a new generation of physically motivated emission and pulse-profile models. The library currently includes some 2000 individual RXTE-PCA, 200 Chandra ACIS-I, and 120 XMM-PN observations of the SMC spanning 15 years, creating an unrivaled record of pulsar temporal behavior. In Phase-2, additional observations of SMC pulsars will be added: 221 Chandra (ACIS-S and ACIS-I), 22 XMM-PN, 142 XMM-MOS, 92 Suzaku, 25 NuSTAR, and >10,000 Swift; leveraging our pipeline and analysis techniques already developed. With the addition of 7 Galactic pulsars each having many hundred multisatellite observations, these datasets cover the entire range of variability timescales and accretion regimes. We will model the pulse-profiles using state of the art techniques to parameterize their morphology and obtain the distribution of offsets between magnetic and spin axes, and create samples of profiles under specific accretion modes (whether pencil-beam or fan-beam dominated). These products are needed for the next generation of advances in neutron star theory and modeling. The long-duration of the dataset and “whole-galaxy" nature of the SMC sample make possible a new statistical approach to uncover the duty-cycle distribution and hence population demographics of transient High Mass X

Pulsar Wind Nebulae Created by Fast-Moving Pulsars

OpenAIRE

Kargaltsev, Oleg; Pavlov, George G.; Klingler, Noel; Rangelov, Blagoy

2017-01-01

We review multiwavelength properties of pulsar wind nebulae (PWNe) created by supersonically moving pulsars and the effects of pulsar motion on the PWN morphologies and the ambient medium. Supersonic pulsar wind nebulae (SPWNe) are characterized by bow-shaped shocks around the pulsar and/or cometary tails filled with the shocked pulsar wind. In the past several years significant advances in SPWN studies have been made in deep observations with the Chandra and XMM-Newton X-ray Observatories as...

Fermi LAT Detection of Pulsed Gamma-Rays From the Vela-Like Pulsars PSR J1048-5832 and PSR J2229+6114

Energy Technology Data Exchange (ETDEWEB)

Abdo, A.A.; /Naval Research Lab, Wash., D.C. /Federal City Coll.; Ackermann, M.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Ajello, M.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Atwood, W.B.; /UC, Santa Cruz; Axelsson, M.; /Stockholm U. /Stockholm U., OKC; Baldini, L.; /INFN, Pisa; Ballet, J.; /DAPNIA, Saclay; Barbiellini, G.; /INFN, Trieste /Trieste U.; Baring, M.G.; /Rice U.; Bastieri, D.; /INFN, Padua /Padua U.; Baughman, B.M.; /Ohio State U.; Bechtol, K.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bellazzini, R.; /INFN, Pisa; Berenji, B.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bloom, E.D.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bonamente, E.; /INFN, Perugia /Perugia U.; Borgland, A.W.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bregeon, J.; /INFN, Pisa; Brez, A.; /INFN, Pisa; Brigida, M.; /Bari U. /INFN, Bari; Bruel, P.; /Ecole Polytechnique /Bari U. /INFN, Bari /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Columbia U. /IASF, Milan /Milan Polytechnic /DAPNIA, Saclay /INFN, Perugia /Perugia U. /Naval Research Lab, Wash., D.C. /George Mason U. /NASA, Goddard /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /INFN, Perugia /Perugia U. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /LPCE, Orleans /Montpellier U. /Stockholm U. /Stockholm U., OKC /INFN, Trieste /Bari U. /INFN, Bari /UC, Santa Cruz /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /CENBG, Gradignan /CENBG, Gradignan /Montpellier U. /Bari U. /INFN, Bari /INFN, Trieste /Arecibo Observ. /Hiroshima U. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Bari U. /INFN, Bari /INFN, Bari /NASA, Goddard /Maryland U. /INFN, Perugia /Perugia U.; /more authors..

2012-03-29

We report the detection of {gamma}-ray pulsations ({ge}0.1 GeV) from PSR J2229+6114 and PSR J1048-5832, the latter having been detected as a low-significance pulsar by EGRET. Data in the {gamma}-ray band were acquired by the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope, while the radio rotational ephemerides used to fold the {gamma}-ray light curves were obtained using the Green Bank Telescope, the Lovell telescope at Jodrell Bank, and the Parkes Telescope. The two young radio pulsars, located within the error circles of the previously unidentified EGRET sources 3EG J1048-5840 and 3EG J2227+6122, present spin-down characteristics similar to the Vela pulsar. PSR J1048-5832 shows two sharp peaks at phases 0.15 {+-} 0.01 and 0.57 {+-} 0.01 relative to the radio pulse confirming the EGRET light curve, while PSR J2229+6114 presents a very broad peak at phase 0.49 {+-} 0.01. The {gamma}-ray spectra above 0.1 GeV of both pulsars are fit with power laws having exponential cutoffs near 3 GeV, leading to integral photon fluxes of (2.19 {+-} 0.22 {+-} 0.32) x 10{sup -7} cm{sup -2} s{sup -1} for PSR J1048-5832 and (3.77 {+-} 0.22 {+-} 0.44) x 10{sup -7} cm{sup -2} s{sup -1} for PSR J2229+6114. The first uncertainty is statistical and the second is systematic. PSR J1048-5832 is one of the two LAT sources which were entangled together as 3EG J1048-5840. These detections add to the growing number of young {gamma}-ray pulsars that make up the dominant population of GeV {gamma}-ray sources in the Galactic plane.

Quasi-periodic Pulse Amplitude Modulation in the Accreting Millisecond Pulsar IGR J00291+5934

Energy Technology Data Exchange (ETDEWEB)

Bult, Peter [Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Doesburgh, Marieke van; Klis, Michiel van der [Anton Pannekoek Institute, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands)

2017-08-20

We introduce a new method for analyzing the aperiodic variability of coherent pulsations in accreting millisecond X-ray pulsars (AMXPs). Our method involves applying a complex frequency correction to the time-domain light curve, allowing for the aperiodic modulation of the pulse amplitude to be robustly extracted in the frequency domain. We discuss the statistical properties of the resulting modulation spectrum and show how it can be correlated with the non-pulsed emission to determine if the periodic and aperiodic variability are coupled processes. Using this method, we study the 598.88 Hz coherent pulsations of the AMXP IGR J00291+5934 as observed with the Rossi X-ray Timing Explorer and XMM-Newton . We demonstrate that our method easily confirms the known coupling between the pulsations and a strong 8 mHz quasi-periodic oscillation (QPO) in XMM-Newton observations. Applying our method to the RXTE observations, we further show, for the first time, that the much weaker 20 mHz QPO and its harmonic are also coupled with the pulsations. We discuss the implications of this coupling and indicate how it may be used to extract new information on the underlying accretion process.

Quasi-Periodic Pulse Amplitude Modulation in the Accreting Millisecond Pulsar IGR J00291+5934

Science.gov (United States)

Bult, Peter; van Doesburgh, Marieke; van der Klis, Michiel

2017-01-01

We introduce a new method for analyzing the a periodic variability of coherent pulsations in accreting millisecond X-ray pulsars (AMXPs). Our method involves applying a complex frequency correction to the time-domain lightcurve, allowing for the aperiodic modulation of the pulse amplitude to be robustly extracted in the frequency domain. We discuss the statistical properties of the resulting modulation spectrum and show how it can be correlated with the non-pulsed emission to determine if the periodic and a periodic variability are coupled processes. Using this method, we study the 598.88 Hz coherent pulsations of the AMXP IGR J00291+5934 as observed with the Rossi X-ray Timing Explorer and XMM-Newton. We demonstrate that our method easily confirms the known coupling between the pulsations and a strong 8 mHz quasi-periodic oscillation (QPO) in XMM-Newton observations. Applying our method to the RXTE observations, we further show, for the first time, that the much weaker 20 mHz QPO and its harmonic are also coupled with the pulsations. We discuss the implications of this coupling and indicate how it may be used to extract new information on the underlying accretion process.

Current Sheets in Pulsar Magnetospheres and Winds: Particle Acceleration and Pulsed Gamma Ray Emission

Science.gov (United States)

Arons, Jonathan

electric current that separate regions of differing magnetization into the domain of highly relativistic magnetic fields - those with energy density large compared to the rest mass energy of the charged particles - the plasma - caught in that field. The investigators will create theoretical and computational models of the magnetic dissipation - a form of viscous flow in the thin sheets of electric current that form in the magnetized regions around the rotating stars - using Particle in-Cell plasma simulations. These simulations use a large computer to solve the equations of motion of many charged particles - millions to billions in the research that will be pursued - to unravel the dissipation of those fields and the acceleration of beams of particles in the thin sheets. The results will be incorporated into macroscopic MHD models of the magnetic structures around the stars which determine the location and strength of the current sheets, so as to model and analyze the pulsed gamma ray emission seen from hundreds of Rotation Powered Pulsars. The computational models will be assisted by ``pencil and paper'' theoretical modeling designed to motivate and interpret the computer simulations, and connect them to the observations.

Optimal Frequency Ranges for Sub-Microsecond Precision Pulsar Timing

Science.gov (United States)

Lam, Michael Timothy; McLaughlin, Maura; Cordes, James; Chatterjee, Shami; Lazio, Joseph

2018-01-01

Precision pulsar timing requires optimization against measurement errors and astrophysical variance from the neutron stars themselves and the interstellar medium. We investigate optimization of arrival time precision as a function of radio frequency and bandwidth. We find that increases in bandwidth that reduce the contribution from receiver noise are countered by the strong chromatic dependence of interstellar effects and intrinsic pulse-profile evolution. The resulting optimal frequency range is therefore telescope and pulsar dependent. We demonstrate the results for five pulsars included in current pulsar timing arrays and determine that they are not optimally observed at current center frequencies. We also find that arrival-time precision can be improved by increases in total bandwidth. Wideband receivers centered at high frequencies can reduce required overall integration times and provide significant improvements in arrival time uncertainty by a factor of $\\sim$$\\sqrt{2}$ in most cases, assuming a fixed integration time. We also discuss how timing programs can be extended to pulsars with larger dispersion measures through the use of higher-frequency observations.

Microwave Tokamak Experiment

International Nuclear Information System (INIS)

Anon.

1988-01-01

The Microwave Tokamak Experiment, now under construction at the Laboratory, will use microwave heating from a free-electron laser. The intense microwave pulses will be injected into the tokamak to realize several goals, including a demonstration of the effects of localized heat deposition within magnetically confined plasma, a better understanding of energy confinement in tokamaks, and use of the new free-electron laser technology for plasma heating. The experiment, soon to be operational, provides an opportunity to study dense plasmas heated by powers unprecedented in the electron-cyclotron frequency range required by the especially high magnetic fields used with the MTX and needed for reactors. 1 references, 5 figures, 3 tables

FERMI LARGE AREA TELESCOPE OBSERVATIONS OF GAMMA-RAY PULSARS PSR J1057-5226, J1709-4429, AND J1952+3252

International Nuclear Information System (INIS)

Abdo, A. A.; Ajello, M.; Bechtol, K.; Berenji, B.; Borgland, A. W.; Bouvier, A.; Buehler, R.; Antolini, E.; Bonamente, E.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Brigida, M.; Bruel, P.; Burnett, T. H.

2010-01-01

The Fermi Large Area Telescope (LAT) data have confirmed the pulsed emission from all six high-confidence gamma-ray pulsars previously known from the EGRET observations. We report results obtained from the analysis of 13 months of LAT data for three of these pulsars (PSR J1057-5226, PSR J1709-4429, and PSR J1952+3252) each of which had some unique feature among the EGRET pulsars. The excellent sensitivity of LAT allows more detailed analysis of the evolution of the pulse profile with energy and also of the variation of the spectral shape with phase. We measure the cutoff energy of the pulsed emission from these pulsars for the first time and provide a more complete picture of the emission mechanism. The results confirm some, but not all, of the features seen in the EGRET data.

Timing Solution and Single-pulse Properties for Eight Rotating Radio Transients

Energy Technology Data Exchange (ETDEWEB)

Cui, B.-Y.; McLaughlin, M. A. [Department of Physics and Astronomy West Virginia University Morgantown, WV 26506 (United States); Boyles, J. [Department of Physics and Astronomy West Kentucky University Bowling Green, KY 42101 (United States); Palliyaguru, N. [Physics and Astronomy Department Texas Tech University Lubbock, TX 79409-1051 (United States)

2017-05-01

Rotating radio transients (RRATs), loosely defined as objects that are discovered through only their single pulses, are sporadic pulsars that have a wide range of emission properties. For many of them, we must measure their periods and determine timing solutions relying on the timing of their individual pulses, while some of the less sporadic RRATs can be timed by using folding techniques as we do for other pulsars. Here, based on Parkes and Green Bank Telescope (GBT) observations, we introduce our results on eight RRATs including their timing-derived rotation parameters, positions, and dispersion measures (DMs), along with a comparison of the spin-down properties of RRATs and normal pulsars. Using data for 24 RRATs, we find that their period derivatives are generally larger than those of normal pulsars, independent of any intrinsic correlation with period, indicating that RRATs’ highly sporadic emission may be associated with intrinsically larger magnetic fields. We carry out Lomb–Scargle tests to search for periodicities in RRATs’ pulse detection times with long timescales. Periodicities are detected for all targets, with significant candidates of roughly 3.4 hr for PSR J1623−0841 and 0.7 hr for PSR J1839−0141. We also analyze their single-pulse amplitude distributions, finding that log-normal distributions provide the best fits, as is the case for most pulsars. However, several RRATs exhibit power-law tails, as seen for pulsars emitting giant pulses. This, along with consideration of the selection effects against the detection of weak pulses, imply that RRAT pulses generally represent the tail of a normal intensity distribution.

Timing Solution and Single-pulse Properties for Eight Rotating Radio Transients

Science.gov (United States)

Cui, B.-Y.; Boyles, J.; McLaughlin, M. A.; Palliyaguru, N.

2017-05-01

Rotating radio transients (RRATs), loosely defined as objects that are discovered through only their single pulses, are sporadic pulsars that have a wide range of emission properties. For many of them, we must measure their periods and determine timing solutions relying on the timing of their individual pulses, while some of the less sporadic RRATs can be timed by using folding techniques as we do for other pulsars. Here, based on Parkes and Green Bank Telescope (GBT) observations, we introduce our results on eight RRATs including their timing-derived rotation parameters, positions, and dispersion measures (DMs), along with a comparison of the spin-down properties of RRATs and normal pulsars. Using data for 24 RRATs, we find that their period derivatives are generally larger than those of normal pulsars, independent of any intrinsic correlation with period, indicating that RRATs’ highly sporadic emission may be associated with intrinsically larger magnetic fields. We carry out Lomb-Scargle tests to search for periodicities in RRATs’ pulse detection times with long timescales. Periodicities are detected for all targets, with significant candidates of roughly 3.4 hr for PSR J1623-0841 and 0.7 hr for PSR J1839-0141. We also analyze their single-pulse amplitude distributions, finding that log-normal distributions provide the best fits, as is the case for most pulsars. However, several RRATs exhibit power-law tails, as seen for pulsars emitting giant pulses. This, along with consideration of the selection effects against the detection of weak pulses, imply that RRAT pulses generally represent the tail of a normal intensity distribution.

Pulsar Magnetospheres and Pulsar Winds

OpenAIRE

Beskin, Vasily S.

2016-01-01

Surprisingly, the chronology of nearly 50 years of the pulsar magnetosphere and pulsar wind research is quite similar to the history of our civilization. Using this analogy, I have tried to outline the main results obtained in this field. In addition to my talk, the possibility of particle acceleration due to different processes in the pulsar magnetosphere is discussed in more detail.

Measurements of the plasma density in the FTU tokamak by a pulsed time-of-flight X-wave refractometer

International Nuclear Information System (INIS)

Petrov, V. G.; Petrov, A. A.; Malyshev, A. Yu.; De Benedetti, M.; Tudisco, O.

2008-01-01

On-line control over the plasma density in tokamaks (especially, in long-term discharges) requires reliable measurements of the averaged plasma density. For this purpose, a new method of density measurements-a pulsed time-of-flight plasma refractometry-was developed and tested in the T-11M tokamak. This method allows one to determine the averaged density from the measured time delay of nanosecond microwave pulses propagating through the plasma. For an O-wave, the measured time delay is proportional to the line-averaged density and is independent of the density profile (f>>f p ) τ o ∼ k o 1/f 2 ∫ l N(x)dx. Here, f is the frequency of the probing wave, f p is the plasma frequency, l= 4 a is the path length for two-pass probing in the equatorial plane, a is the plasma minor radius, k O and k X are numerical factors, f c is the electron-cyclotron frequency at the axis of the plasma column, and f p >>f c , f. Measurements of the time delay provide the same information as plasma interferometry, though they do no employ the effect of interference. When the conditions f p >>f c , f are not satisfied, the measured time delay depends on the shape of the density profile. In this case, in order to determine the average density regardless of the density profile, it is necessary to perform simultaneous measurements at several probing frequencies in order to determine the average density. In ITER (Bt ∼ 5T), a spectral window between the lower and upper cutoff frequencies in the range of 50-100 GHz can be used for pulsed time-of-flight X-wave refractometry. This appreciably simplifies the diagnostics and eliminates the problem of the first mirror. In this paper, the first results obtained in the FTU tokamak with a prototype of the ITER pulsed time-of-flight refractometer are presented. The geometry and layout of experiments similar to the planned ITER experiments are described. The density measured by pulsed time-of-flight refractometry is shown to agree well with the

Observations of Accreting Pulsars with the FERMI-GBM

Science.gov (United States)

Wilson-Hodge, Colleen

2012-01-01

The Gamma-ray Burst Monitor (GBM) on-board Fermi comprises 12 NaI detectors spanning the 8-1000 keV band and 2 BGO detectors spanning the 100 keV to 40 MeV band. These detectors view the entire unocculted sky, providing long (approximately 40 ks/day) observations of accreting pulsars daily, which allow long-term monitoring of spin-frequencies and pulsed uxes via epoch-folded searches plus daily blind searches for new pulsars. Phase averaged uxes can be measured using the Earth occultation technique. In this talk I will present highlights of GBM accretion-powered pulsar monitoring such as the discovery of a torque reversal in 4U1626-67, a high-energy QPO in A0535+26, and evidence for a stable accretion disk in OAO 1657-415.

Microwave Tokamak Experiment: Overview and status

International Nuclear Information System (INIS)

1990-05-01

The Microwave Tokamak Experiment, now under construction at the Laboratory, will use microwave heating from a free-electron laser. The intense microwave pulses will be injected into the tokamak to realize several goals, including a demonstration of the effects of localized heat deposition within magnetically confined plasma, a better understanding of energy confinement in tokamaks, and use of the new free-electron laser technology for plasma heating. 3 figs., 3 tabs

Pulsed X-Ray Emission from Pulsar A in the Double Pulsar System J0737-3039

NARCIS (Netherlands)

Chatterjee, S.; Gaensler, B.M.; Melatos, A.; Brisken, W.F.; Stappers, B.W.

2007-01-01

The double pulsar system J0737-3039 is not only a test bed for general relativity and theories of gravity, but also provides a unique laboratory for probing the relativistic winds of neutron stars. Recent X-ray observations have revealed a point source at the position of the J0737-3039 system, but

Pulsar magnetic alignment. The drifting subpulses

International Nuclear Information System (INIS)

Jones, P.B.

1977-01-01

According to Ruderman and Sutherland (Ap.J.;196:51 (1975)) the subpulse drift observed in certain pulsars is a consequence of the circulation around the magnetic axis of electron-positron discharges occurring within an acceleration region near the polar cap. The predicted period of circulation P 3 is of the correct order of magnitude, but the sense of circulation and therefore the direction of subpulse drift is not consistent with indirect evidence, from observed integrated pulse widths, on the variation with pulsar age of the angle between the spin and magnetic axes. It is shown that this problem is resolved by a model of the acceleration electric field based on space charge limited ion flow. (author)

Detections of millisecond pulsars with the FERMI Large Area Telescope

International Nuclear Information System (INIS)

Guillemot, L.

2009-09-01

The Fermi observatory was launched on June 11, 2008. It hosts the Large Area Telescope (LAT), sensitive to gamma-ray photons from 20 MeV to over 300 GeV. When the LAT began its activity, nine young and energetic pulsars were known in gamma ray range. At least several tens of pulsar detections by the LAT were predicted before launch. The LAT also allowed the study of millisecond pulsars (MSPs), never firmly detected in gamma ray range before Fermi. This thesis first presents the pulsar timing campaign for the LAT, in collaboration with large radio telescopes and X-ray telescopes, allowing for high sensitivity pulsed searches. Furthermore, it lead to quasi-homogeneous coverage of the galactic MSPs, so that the search for pulsations in LAT data for this population of stars was not affected by an a-priori bias. We present a search for pulsations from these objects in LAT data. For the first time, eight galactic MSPs have been detected as sources of pulsed gamma-ray emission over 100 MeV. In addition, a couple of good candidates for future detection are seen. A similar search for globular cluster MSPs was not successful so far. Comparison of the phase-aligned gamma-ray and radio light curves, as well as the spectral shapes, leads to the conclusion that their gamma-ray emission is similar to that of normal pulsars, and is probably produced in the outer-magnetosphere. This discovery suggests that many unresolved gamma-ray sources are unknown MSPs. (author)

Spectral analysis of the Crab Pulsar and Nebula with the Fermi Large Area Telescope

International Nuclear Information System (INIS)

Loparco, F.

2011-01-01

The Crab Pulsar is a relatively young neutron star. The Pulsar is the central star in the Crab Nebula, a remnant of the supernova SN 1054, which was observed on Earth in the year 1054. The Crab Pulsar has been extensively observed in the gamma-ray energy band by the Large Area Telescope (LAT), the main instrument onboard the Fermi gamma-ray space telescope, during its first months of data taking. The LAT data have been used to reconstruct the fluxes and the energy spectra of the pulsed gamma-ray component and of the gamma-rays from the Nebula. The results on the pulsed component are in good agreement with the previous measurement from EGRET, while the results on the Nebula are consistent with the observations from Earth based telescopes.

Are the infrared-faint radio sources pulsars?

Science.gov (United States)

Cameron, A. D.; Keith, M.; Hobbs, G.; Norris, R. P.; Mao, M. Y.; Middelberg, E.

2011-07-01

Infrared-faint radio sources (IFRS) are objects which are strong at radio wavelengths but undetected in sensitive Spitzer observations at infrared wavelengths. Their nature is uncertain and most have not yet been associated with any known astrophysical object. One possibility is that they are radio pulsars. To test this hypothesis we undertook observations of 16 of these sources with the Parkes Radio Telescope. Our results limit the radio emission to a pulsed flux density of less than 0.21 mJy (assuming a 50 per cent duty cycle). This is well below the flux density of the IFRS. We therefore conclude that these IFRS are not radio pulsars.

Probing Millisecond Pulsar Emission Geometry Using Light Curves From the Fermi Large Area Telescope

Science.gov (United States)

Venter, Christo; Harding, Alice; Guillemot, L.

2009-01-01

An interesting new high-energy pulsar sub-population is emerging following early discoveries of gamma-ray millisecond pulsars (MSPs) by the Fermi Large Area Telescope (LAT). We present results from 3D emission modeling, including the Special Relativistic effects of aberration and time-of-flight delays and also rotational sweepback of 13-field lines, in the geometric context of polar cap (PC), slot gap (SG), outer gap (OG), and two-pole caustic (TPC) pulsar models. In contrast to the general belief that these very old, rapidly-rotating neutron stars (NSs) should have largely pair-starved magnetospheres due to the absence of significant pair production, we find that most of the light curves are best fit by SG and OG models, which indicates the presence of narrow accelerating gaps limited by robust pair production -- even in these pulsars with very low spin-down luminosities. The gamma-ray pulse shapes and relative phase lags with respect to the radio pulses point to high-altitude emission being dominant for all geometries. We also find exclusive differentiation of the current gamma-ray MSP population into two MSP sub-classes: light curve shapes and lags across wavebands impose either pair-starved PC (PSPC) or SG / OG-type geometries. In the first case, the radio pulse has a small lag with respect to the single gamma-ray pulse, while the (first) gamma-ray peak usually trails the radio by a large phase offset in the latter case. Finally, we find that the flux correction factor as a function of magnetic inclination and observer angles is typically of order unity for all models. Our calculation of light curves and flux correction factor f(_, _, P) for the case of MSPs is therefore complementary to the "ATLAS paper" of Watters et al. for younger pulsars.

FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE VELA PULSAR

International Nuclear Information System (INIS)

Abdo, A. A.; Ackermann, M.; Bartelt, J.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bogart, J. R.; Atwood, W. B.; Bagagli, R.; Baldini, L.; Bellardi, F.; Bellazzini, R.; Ballet, J.; Band, D. L.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bisello, D.; Baughman, B. M.

2009-01-01

The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new γ-ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high-quality pulse profile, with some 32,400 pulsed photons at E ≥ 0.03 GeV, shows new features, including pulse structure as fine as 0.3 ms and a distinct third peak, which shifts in phase with energy. We examine the high-energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power-law index of Γ = 1.51 +0.05 -0.04 with an exponential cutoff at E c = 2.9 ± 0.1 GeV. Spectral fits with generalized cutoffs of the form e -(E/E c ) b require b ≤ 1, which is inconsistent with magnetic pair attenuation, and thus favor outer-magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding pulsar wind nebula.

Gravitational waves from binary supermassive black holes missing in pulsar observations.

Science.gov (United States)

Shannon, R M; Ravi, V; Lentati, L T; Lasky, P D; Hobbs, G; Kerr, M; Manchester, R N; Coles, W A; Levin, Y; Bailes, M; Bhat, N D R; Burke-Spolaor, S; Dai, S; Keith, M J; Osłowski, S; Reardon, D J; van Straten, W; Toomey, L; Wang, J-B; Wen, L; Wyithe, J S B; Zhu, X-J

2015-09-25

Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers. A stochastic superposition of gravitational waves from all such binary systems would modulate the arrival times of pulses from radio pulsars. Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrained the characteristic amplitude of this background, A(c,yr), to be gravitational waves. Copyright © 2015, American Association for the Advancement of Science.

Black Hole/Pulsar Binaries in the Galaxy

Science.gov (United States)

Shao, Yong; Li, Xiang-Dong

2018-04-01

We have performed population synthesis calculation on the formation of binaries containing a black hole (BH) and a neutron star (NS) in the Galactic disk. Some of important input parameters, especially for the treatment of common envelope evolution, are updated in the calculation. We have discussed the uncertainties from the star formation rate of the Galaxy and the velocity distribution of NS kicks on the birthrate (˜ 0.6-13 Myr^{-1}) of BH/NS binaries. From incident BH/NS binaries, by modelling the orbital evolution duo to gravitational wave radiation and the NS evolution as radio pulsars, we obtain the distributions of the observable parameters such as the orbital period, eccentricity and pulse period of the BH/pulsar binaries. We estimate that there may be ˜3 - 80 BH/pulsar binaries in the Galactic disk and around 10% of them could be detected by the Five-hundred-meter Aperture Spherical radio Telescope.

Black hole/pulsar binaries in the Galaxy

Science.gov (United States)

Shao, Yong; Li, Xiang-Dong

2018-06-01

We have performed population synthesis calculation on the formation of binaries containing a black hole (BH) and a neutron star (NS) in the Galactic disc. Some of important input parameters, especially for the treatment of common envelope evolution, are updated in the calculation. We have discussed the uncertainties from the star formation rate of the Galaxy and the velocity distribution of NS kicks on the birthrate (˜ 0.6-13 M yr^{-1}) of BH/NS binaries. From incident BH/NS binaries, by modelling the orbital evolution due to gravitational wave radiation and the NS evolution as radio pulsars, we obtain the distributions of the observable parameters such as the orbital period, eccentricity, and pulse period of the BH/pulsar binaries. We estimate that there may be ˜3-80 BH/pulsar binaries in the Galactic disc and around 10 per cent of them could be detected by the Five-hundred-metre Aperture Spherical radio Telescope.

EFFECTS OF INTERMITTENT EMISSION: NOISE INVENTORY FOR THE SCINTILLATING PULSAR B0834+06

International Nuclear Information System (INIS)

Gwinn, C. R.; Johnson, M. D.; Smirnova, T. V.; Stinebring, D. R.

2011-01-01

We compare signal and noise for observations of the scintillating pulsar B0834+06, using very long baseline interferometry and a single-dish spectrometer. Comparisons between instruments and with models suggest that amplitude variations of the pulsar strongly affect the amount and distribution of self-noise. We show that noise follows a quadratic polynomial with flux density, in spectral observations. Constant coefficients, indicative of background noise, agree well with expectation; whereas second-order coefficients, indicative of self-noise, are ∼3 times values expected for a pulsar with constant on-pulse flux density. We show that variations in flux density during the 10 s integration accounts for the discrepancy. In the secondary spectrum, ∼97% of spectral power lies within the pulsar's typical scintillation bandwidth and timescale; an extended scintillation arc contains ∼3%. For a pulsar with constant on-pulse flux density, noise in the dynamic spectrum will appear as a uniformly distributed background in the secondary spectrum. We find that this uniform noise background contains 95% of noise in the dynamic spectrum for interferometric observations; but only 35% of noise in the dynamic spectrum for single-dish observations. Receiver and sky dominate noise for our interferometric observations, whereas self-noise dominates for single-dish. We suggest that intermittent emission by the pulsar, on timescales <300 μs, concentrates self-noise near the origin in the secondary spectrum, by correlating noise over the dynamic spectrum. We suggest that intermittency sets fundamental limits on pulsar astrometry or timing. Accounting of noise may provide means for detection of intermittent sources, when effects of propagation are unknown or impractical to invert.

System engineering and design of a pulsed homopolar generator power supply for the Texas Experimental Tokamak

International Nuclear Information System (INIS)

Bird, W.L.; Grant, G.B.; Weldon, W.F.; Rylander, H.G.; Woodson, H.H.

1977-01-01

The design of a homopolar generator power supply for the Texas Experimental Tokamak (TEXT) is presented. Four series-connected disk type homopolar machines serve as inertial energy storage and conversion devices to supply 50 to 70 MW peak power to the toroidal field coil and ohmic heating coil circuits. The system is nominally operated at 150 MJ, 430 V to provide a 0.5 sec flat top, 160 kA TF current pulse and a 0.3 sec, 10 kA OH current pulse every 2.0 min on a continuous basis. The system has a maximum capacity of 200 MJ at a maximum open circuit voltage of 500 V. The homopolar machine design is described

Large Aspect Ratio Tokamak Study

International Nuclear Information System (INIS)

Reid, R.L.; Holmes, J.A.; Houlberg, W.A.; Peng, Y.K.M.; Strickler, D.J.; Brown, T.G.; Wiseman, G.W.

1980-06-01

The Large Aspect Ratio Tokamak Study (LARTS) at Oak Ridge National Laboratory (ORNL) investigated the potential for producing a viable longburn tokamak reactor by enhancing the volt-second capability of the ohmic heating transformer through the use of high aspect ratio designs. The plasma physics, engineering, and economic implications of high aspect ratio tokamaks were assessed in the context of extended burn operation. Using a one-dimensional transport code plasma startup and burn parameters were addressed. The pulsed electrical power requirements for the poloidal field system, which have a major impact on reactor economics, were minimized by optimizing the startup and shutdown portions of the tokamak cycle. A representative large aspect ratio tokamak with an aspect ratio of 8 was found to achieve a burn time of 3.5 h at capital cost only approx. 25% greater than that of a moderate aspect ratio design tokamak

Conceptual design of PF coil system and operation scenario on inductively-operated day-long pulsed tokamak reactor

International Nuclear Information System (INIS)

Wang, J.F.; Yamamoto, T.; Ogawa, Y.

1994-01-01

It is said that disadvantages of pulsed operation in tokamak fusion reactor are fatigue problem of structural materials and an introduction of energy storage System to compensate the power during the dwell time. To overcome theses disadvantages the authors have designed an inductively-operated ultralong pulsed tokamak called (IDLT) reactor where plasma with a major radius of 10 m are employed so as to provide a magnetic flux necessary to sustain a plasma current inductively during 10 hours or more. This makes it possible to reduce the total cycle number to be around 10 4 during the life of the fusion plant. In pulsed operation reactors the shorter dwell time with a quick start-up and shut down of plasma is very convenient to realize a high availability of the power plant, but it will induce more severe conditions for the hardware design. The authors assumed the dwell time of 5∼10 minutes and analyzed the feasibility of plasma operation scenario for IDLT reactor, especially paying much attention to PF coil system. The stored energy of PF coil system becomes ∼100 GJ, which is comparable with that of toroidal field coil system. When the plasma current of 14 MA is ramped up with a time of 100 seconds, it is found that the maximum capacity of 1 GW is necessary for PF coil power supply. Engineering issues related with AC/hysterisis loss should be carefully examined

LONG-TERM X-RAY MONITORING OF THE YOUNG PULSAR PSR B1509–58

International Nuclear Information System (INIS)

Livingstone, Margaret A.; Kaspi, Victoria M.

2011-01-01

It has long been thought that the pulsed X-ray properties of rotation-powered pulsars are stable on long timescales. However, long-term, systematic studies of individual sources have been lacking. Furthermore, dramatic X-ray variability has now been observed from two pulsars having inferred sub-critical dipole magnetic fields. Here we present an analysis of the long-term pulsed X-ray properties of the young, energetic pulsar PSR B1509–58 using data from the Rossi X-ray Timing Explorer. We measured the 2-50 keV pulsed flux for 14.7 yr of X-ray observations and found that it is consistent with being constant on all relevant timescales, and place a 3σ upper limit on day-to-week variability of <28%. In addition, we searched for magnetar-like X-ray bursts in all observations and found none, which we use to constrain the measurable burst rate to less than one per 750 ks of observations. We also searched for variability in the pulse profile and found that it is consistent with being stable on timescales of days to decades. This supports the hypothesis that X-ray properties of rotation-powered X-ray pulsars can be stable on decade-long timescales. In addition, we extend the existing timing solution by 7.1 yr to a total of 28.4 yr and report updated values of the braking index, n = 2.832 ± 0.003, and the second braking index, m = 17.6 ± 1.9.

High performance operational limits of tokamak and helical systems

International Nuclear Information System (INIS)

Yamazaki, Kozo; Kikuchi, Mitsuru

2003-01-01

The plasma operational boundaries of tokamak and helical systems are surveyed and compared with each other. Global confinement scaling laws are similar and gyro-Bohm like, however, local transport process is different due to sawtooth oscillations in tokamaks and ripple transport loss in helical systems. As for stability limits, achievable tokamak beta is explained by ideal or resistive MHD theories. On the other hand, beta values obtained so far in helical system are beyond ideal Mercier mode limits. Density limits in tokamak are often related to the coupling between radiation collapse and disruptive MHD instabilities, but the slow radiation collapse is dominant in the helical system. The pulse length of both tokamak and helical systems is on the order of hours in small machines, and the longer-pulsed good-confinement plasma operations compatible with radiative divertors are anticipated in both systems in the future. (author)

Spectral and Temporal Properties of the Ultra-Luminous X-Ray Pulsar in M82 from 15 Years of Chandra Observations and Analysis of the Pulsed Emission Using NuSTAR

Science.gov (United States)

Brightman, Murray; Harrison, Fiona; Walton, Dominic J.; Fuerst, Felis; Zezas, Andreas; Bachetti, Matteo; Grefenstette, Brian; Ptak, Andrew; Tendulkar, Shriharsh; Yukita, Mihoko

2016-01-01

The recent discovery by Bachetti et al. of a pulsar in M82 that can reach luminosities of up to 10(exp 40) erg s(exp -1), a factor of approximately 100 times the Eddington luminosity for a 1.4 solar mass compact object, poses a challenge for accretion physics. In order to better understand the nature of this source and its duty cycle, and in light of several physical models that have been subsequently published, we conduct a spectral and temporal analysis of the 0.58 keV X-ray emission from this source from 15 years of Chandra observations. We analyze 19 ACIS observations where the point-spread function (PSF) of the pulsar is not contaminated by nearby sources. We fit the Chandra spectra of the pulsar with a power-law model and a disk blackbody model, subjected to interstellar absorption in M82. We carefully assess for the effect of pile-up in our observations, where four observations have a pile-up fraction of 10, which we account for during spectral modeling with a convolution model. When fitted with a power-law model, the average photon index when the source is at high luminosity (LX greater than 10(exp 39) erg s(exp -1) is equal to gamma 1.33 +/-.0.15. For the disk blackbody model, the average temperature is T(sub in) 3.24 +/- 0.65 keV, the spectral shape being consistent with other luminous X-ray pulsars. We also investigated the inclusion of a soft excess component and spectral break, finding that the spectra are also consistent with these features common to luminous X-ray pulsars. In addition, we present spectral analysis from NuSTAR over the 3-50 keV range where we have isolated the pulsed component. We find that the pulsed emission in this band is best fit by a power-law with a high-energy cutoff, where gamma is equal to 0.6 +/- 0.3 and E(sub C) is equal to 14(exp +5) (sub -3)) keV. While the pulsar has previously been identified as a transient, we find from our longer-baseline study that it has been remarkably active over the 15-year period, where for 9

TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

Science.gov (United States)

Kaspi, Victoria

2011-09-01

The past decade has seen major progress in neutron star astrophysics, with the discovery of magnetars in general, and the recognition that the Anomalous X-ray Pulsars (AXPs) fall in this class. AXPs have recently revealed surprising and dramatic variability behavior, which theorists have begun to show are highly constraining of physical models of magnetars, including their crusts, atmospheres, coronae and magnetospheres. In this proposal, we request Chandra/ACIS-S Target-of-Opportunity observations of one major Anomalous X-ray Pulsar (AXP) outburst in AO13, in order to study in detail the evolution of the spectrum, pulsed fraction and pulse profile, for quantitative confrontation with recently developed models for the structure and electrodynamics of magnetars.

Searching for Single Pulses Using Heimdall

Science.gov (United States)

Walsh, Gregory; Lynch, Ryan

2018-01-01

In radio pulsar surveys, the interstellar medium causes a frequency dependent dispersive delay of a pulsed signal across the observing band. If not corrected, this delay substantially lowers S/N and makes most pulses undetectable. The delay is proportional to an unknown dispersion measure (DM), which must be searched over with many trial values. A number of new, GPU-accelerated codes are now available to optimize this dedispersion task, and to search for transient pulsed radio emission. We report on the use of Heimdall, one such GPU-accelerated tree dedispersion utility, to search for transient radio sources in a Green Bank Telescope survey of the Cygnus Region and North Galactic Plane. The survey is carried out at central frequency of 820 MHz with a goal of finding Fast Radio Bursts, Rotating Radio Transients, young pulsars, and millisecond pulsars. We describe the the survey, data processing pipeline, and follow-up of candidate sources.

MAST: a Mega Amp Spherical Tokamak

International Nuclear Information System (INIS)

Darke, A.C.; Harbar, J.R.; Hay, J.H.; Hicks, J.B.; Hill, J.W.; McKenzie, J.S.; Morris, A.W.; Nightingale, M.P.S.; Todd, T.N.; Voss, G.M.; Watkins, J.R.

1995-01-01

The highly successful tight aspect ratio tokamak research pioneered on the START machine at Culham, together with the attractive possibilities of the concept, suggest a larger device should be considered. The design of a Mega Amp Spherical Tokamak is described, operating at much higher currents and over longer pulses than START and compatible with strong additional heating. (orig.)

Ensemble candidate classification for the LOTAAS pulsar survey

Science.gov (United States)

Tan, C. M.; Lyon, R. J.; Stappers, B. W.; Cooper, S.; Hessels, J. W. T.; Kondratiev, V. I.; Michilli, D.; Sanidas, S.

2018-03-01

One of the biggest challenges arising from modern large-scale pulsar surveys is the number of candidates generated. Here, we implemented several improvements to the machine learning (ML) classifier previously used by the LOFAR Tied-Array All-Sky Survey (LOTAAS) to look for new pulsars via filtering the candidates obtained during periodicity searches. To assist the ML algorithm, we have introduced new features which capture the frequency and time evolution of the signal and improved the signal-to-noise calculation accounting for broad profiles. We enhanced the ML classifier by including a third class characterizing RFI instances, allowing candidates arising from RFI to be isolated, reducing the false positive return rate. We also introduced a new training data set used by the ML algorithm that includes a large sample of pulsars misclassified by the previous classifier. Lastly, we developed an ensemble classifier comprised of five different Decision Trees. Taken together these updates improve the pulsar recall rate by 2.5 per cent, while also improving the ability to identify pulsars with wide pulse profiles, often misclassified by the previous classifier. The new ensemble classifier is also able to reduce the percentage of false positive candidates identified from each LOTAAS pointing from 2.5 per cent (˜500 candidates) to 1.1 per cent (˜220 candidates).

DID THE CRAB PULSAR UNDERGO A SMALL GLITCH IN 2006 LATE MARCH/EARLY APRIL?

Energy Technology Data Exchange (ETDEWEB)

Vivekanand, M., E-mail: viv.maddali@gmail.com [No. 24, NTI Layout 1st Stage, 3rd Main, 1st Cross, Nagasettyhalli, Bangalore 560094 (India)

2016-08-01

On 2006 August 23 the Crab Pulsar underwent a glitch, which was reported by the Jodrell Bank and the Xinjiang radio observatories. Neither data are available to the public. However, the Jodrell group publishes monthly arrival times of the Crab Pulsar pulse (their actual observations are done daily), and using these, it is shown that about 5 months earlier the Crab Pulsar probably underwent a small glitch, which has not been reported before. Neither observatory discusses the detailed analysis of data from 2006 March to August; either they may not have detected this small glitch, or they may have attributed it to timing noise in the Crab Pulsar. The above result is verified using X-ray data from RXTE . If this is indeed true, this is probably the smallest glitch observed in the Crab Pulsar so far, whose implications are discussed. This work addresses the confusion possible between small-magnitude glitches and timing noise in pulsars.

HESTER: a hot-electron superconducting tokamak experimental reactor at M.I.T

International Nuclear Information System (INIS)

Schultz, J.H.; Montgomery, D.B.

1983-04-01

HESTER is an experimental tokamak, designed to resolve many of the central questions in the tokamak development program in the 1980's. It combines several unique features with new perspectives on the other major tokamak experiments scheduled for the next decade. The overall objectives of HESTER, in rough order of their presently perceived importance, are the achievement of reactor-like wall-loadings and plasma parameters for long pulse periods, determination of a good, reactor-relevant method of steady-state or very long pulse tokamak current drive, duplication of the planned very high temperature neutral injection experiments using only radio frequency heating, a demonstration of true steady-state tokamak operation, integration of a high-performance superconducting magnet system into a tokamak experiment, determination of the best methods of long term impurity control, and studies of transport and pressure limits in high field, high aspect ratio tokamak plasmas. These objectives are described

The Velocity Distribution of Isolated Radio Pulsars

Science.gov (United States)

Arzoumanian, Z.; Chernoff, D. F.; Cordes, J. M.; White, Nicholas E. (Technical Monitor)

2002-01-01

We infer the velocity distribution of radio pulsars based on large-scale 0.4 GHz pulsar surveys. We do so by modelling evolution of the locations, velocities, spins, and radio luminosities of pulsars; calculating pulsed flux according to a beaming model and random orientation angles of spin and beam; applying selection effects of pulsar surveys; and comparing model distributions of measurable pulsar properties with survey data using a likelihood function. The surveys analyzed have well-defined characteristics and cover approx. 95% of the sky. We maximize the likelihood in a 6-dimensional space of observables P, dot-P, DM, absolute value of b, mu, F (period, period derivative, dispersion measure, Galactic latitude, proper motion, and flux density). The models we test are described by 12 parameters that characterize a population's birth rate, luminosity, shutoff of radio emission, birth locations, and birth velocities. We infer that the radio beam luminosity (i) is comparable to the energy flux of relativistic particles in models for spin-driven magnetospheres, signifying that radio emission losses reach nearly 100% for the oldest pulsars; and (ii) scales approximately as E(exp 1/2) which, in magnetosphere models, is proportional to the voltage drop available for acceleration of particles. We find that a two-component velocity distribution with characteristic velocities of 90 km/ s and 500 km/ s is greatly preferred to any one-component distribution; this preference is largely immune to variations in other population parameters, such as the luminosity or distance scale, or the assumed spin-down law. We explore some consequences of the preferred birth velocity distribution: (1) roughly 50% of pulsars in the solar neighborhood will escape the Galaxy, while approx. 15% have velocities greater than 1000 km/ s (2) observational bias against high velocity pulsars is relatively unimportant for surveys that reach high Galactic absolute value of z distances, but is severe for

Light curve and pulse profile of the x-ray pulsar Vela X-1

International Nuclear Information System (INIS)

Nagase, Fumiaki; Hayakawa, Satio; Makino, Fumiyoshi; Sato, Naohisa; Makishima, Kazuo.

1983-01-01

The following properties of the X-ray binary pulsar Vela X-1 are presented by reference to its observations in March 1980. The light curve shows a high state and a low state in the first and second halves of an orbital period, respectively, but they may rather be defined as a soft state and hard state, respectively, since the intensity above 9 keV does not appreciably change between these two states. The energy spectra in these states indicate the presence of circumstellar absorption. The pulse profiles at high (9-22 keV) and low (1-9 keV) energies are different, indicating the absorption by cold matter which is probably in the accretion column. The absorber which is responsible for the soft and hard states is attributed to the stellar wind whose flow pattern is consistent with that obtained from optical absorption spectra. The orbital period is obtained by a combined analysis of X-ray data since 1972. No appreciable change of the period gives a constraint on the dynamical behavior of the binary system. (author)

Tokamak experiments on JIPP T-II with pulsed gas injection

International Nuclear Information System (INIS)

Toi, K.; Itoh, S.; Fujita, J.; Kadota, K.; Kawahata, K.

1978-02-01

The confinement of tokamak plasma has been investigated in the wide range of electron density average n sub(e) from 1 x 10 13 to 5 x 10 13 cm -3 by using the pulsed gas injection. The gross energy confinement time increases with increase of electron density and reaches 14 msec. The averaged effective ionic charge derived from plasma conductivity = is about 1 to 2 in the regime of small streaming parameter ( = 0.01 -- 0.08). The ratio of ion temperature to electron one is in the range greater than 0.5. This fact means that the ion energy confinement time is greater than the electron-ion energy relaxation time. Excessive injection of cold neutral gas excites m = 2 MHD oscillations. Much more gas injection leads to the remarkable cooling of plasma periphery and disruptive instabilities. These MHD oscillations and disruptive instabilities have been suppressed by the heating of plasma periphery with the second rapid rise of plasma current. (auth.)

The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars

Science.gov (United States)

Arzoumanian, Zaven; Brazier, Adam; Burke-Spolaor, Sarah; Chamberlin, Sydney; Chatterjee, Shami; Christy, Brian; Cordes, James M.; Cornish, Neil J.; Crawford, Fronefield; Thankful Cromartie, H.; Crowter, Kathryn; DeCesar, Megan E.; Demorest, Paul B.; Dolch, Timothy; Ellis, Justin A.; Ferdman, Robert D.; Ferrara, Elizabeth C.; Fonseca, Emmanuel; Garver-Daniels, Nathan; Gentile, Peter A.; Halmrast, Daniel; Huerta, E. A.; Jenet, Fredrick A.; Jessup, Cody; Jones, Glenn; Jones, Megan L.; Kaplan, David L.; Lam, Michael T.; Lazio, T. Joseph W.; Levin, Lina; Lommen, Andrea; Lorimer, Duncan R.; Luo, Jing; Lynch, Ryan S.; Madison, Dustin; Matthews, Allison M.; McLaughlin, Maura A.; McWilliams, Sean T.; Mingarelli, Chiara; Ng, Cherry; Nice, David J.; Pennucci, Timothy T.; Ransom, Scott M.; Ray, Paul S.; Siemens, Xavier; Simon, Joseph; Spiewak, Renée; Stairs, Ingrid H.; Stinebring, Daniel R.; Stovall, Kevin; Swiggum, Joseph K.; Taylor, Stephen R.; Vallisneri, Michele; van Haasteren, Rutger; Vigeland, Sarah J.; Zhu, Weiwei; The NANOGrav Collaboration

2018-04-01

We present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, aimed at detecting and characterizing low-frequency gravitational waves. The pulsars were observed with the Arecibo Observatory and/or the Green Bank Telescope at frequencies ranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximately monthly cadence, and six high-timing-precision pulsars were observed weekly. All were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. We describe our methods for data processing, time-of-arrival (TOA) calculation, and the implementation of a new, automated method for removing outlier TOAs. We fit a timing model for each pulsar that includes spin, astrometric, and (for binary pulsars) orbital parameters; time-variable dispersion delays; and parameters that quantify pulse-profile evolution with frequency. The timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of significant orbital-period variations. We fit models that characterize sources of noise for each pulsar. We find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. A companion paper uses these data to constrain the strength of the gravitational-wave background.

First Results from Tests of High Temperature Superconductor Magnets on Tokamak

Energy Technology Data Exchange (ETDEWEB)

Gryaznevich, M.; Todd, T.T., E-mail: mikhail.gryaznevich@ccfe.ac.uk [Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon (United Kingdom); Svoboda, V.; Markovic, T.; Ondrej, G. [Czech Technical University, Prague (Czech Republic); Stockel, J.; Duran, I.; Kovarik, K. [IPP Prague, Czech Technical University, Prague (Czech Republic); Sykes, A.; Kingham, D. [Tokamak Solutions, Culham Science Centre, Abingdon (United Kingdom); Melhem, Z.; Ball, S.; Chappell, S. [Oxford Instruments, Abingdon (United Kingdom); Lilley, M. K.; De Grouchy, P.; Kim, H. -T. [Imperial College, London (United Kingdom)

2012-09-15

Full text: It has long been known that high temperature superconductors (HTS) could have an important role to play in the future of tokamak fusion research. Here we report on first results of the use of HTS in a tokamak magnet and on the progress in design and construction of the first fully-HTS tokamak. In the experiment, the two copper vertical field coils of the small tokamak GOLEM were replaced by two coils each with 6 turns of HTS (Re)BCO tape. Liquid nitrogen was used to cool the coils to below the critical temperature at which HTS becomes superconducting. Little effect on the HTS critical current has been observed for perpendicular field up to 0.5 T and superconductivity has been achieved at {approx} 90.5K during bench tests. There had been concerns that the plasma pulses and pulsed magnetic fields might cause a 'quench' in the HTS, i.e., a sudden and potentially damaging transition from superconductor to normal conductor. However, many plasma pulses were fired without any quenches even when disruptions occurred with corresponding induced electrical fields. In addition, experiments without plasma have been performed to study properties of the HTS in a tokamak environment, i.e., critical current and its dependence on magnetic and electrical fields generated in a tokamak both in DC and pulsed operations, maximum current ramp-up speed, performance of the HTS tape after number of artificially induced quenches etc. No quench has been observed at DC currents up to 200 A (1.2 kA-turns through the coil). In short pulses, current up to 1 kA through the tape (6 kA-turns) has been achieved with no subsequent degradation of the HTS performance with a current ramp rate up to 0.6 MA/s. In future experiments, increases in both the plasma current and pulse duration are planned. Considerable experience has been gained during design and fabrication of the cryostat, coils, isolation and insulation, feeds and cryosystems, and GOLEM is now routinely operated with HTS coils. The

Implications of the Occurrence of Glitches in Pulsar Free Precession Candidates.

Science.gov (United States)

Jones, D I; Ashton, G; Prix, R

2017-06-30

The timing properties of radio pulsars provide a unique probe of neutron star interiors. Recent observations have uncovered quasiperiodicities in the timing and pulse properties of some pulsars, a phenomenon that has often been attributed to free precession of the neutron star, with profound implications for the distribution of superfluidity and superconductivity in the star. We advance this program by developing consistency relations between free precession and pulsars glitches, and we show that there are difficulties in reconciling the two phenomena in some precession candidates. This indicates that the precession model used here needs to be modified or some other phenomenon is at work in producing the quasiperiodicities, or even that there is something missing in terms of our understanding of glitches.

Magnetic Pair Creation Attenuation Altitude Constraints in Gamma-Ray Pulsars

Science.gov (United States)

Baring, Matthew; Story, Sarah

The Fermi gamma-ray pulsar database now exceeds 150 sources and has defined an important part of Fermi's science legacy, providing rich information for the interpretation of young energetic pulsars and old millisecond pulsars. Among the well established population characteristics is the common occurrence of exponential turnovers in the 1-10 GeV range. These turnovers are too gradual to arise from magnetic pair creation in the strong magnetic fields of pulsar inner magnetospheres, so their energy can be used to provide lower bounds to the typical altitude of GeV band emission. We explore such constraints due to single-photon pair creation transparency at and below the turnover energy. Our updated computations span both domains when general relativistic influences are important and locales where flat spacetime photon propagation is modified by rotational aberration effects. The altitude bounds, typically in the range of 2-5 stellar radii, provide key information on the emission altitude in radio quiet pulsars that do not possess double-peaked pulse profiles. However, the exceptional case of the Crab pulsar provides an altitude bound of around 20% of the light cylinder radius if pair transparency persists out to 350 GeV, the maximum energy detected by MAGIC. This is an impressive new physics-based constraint on the Crab's gamma-ray emission locale.

MHD stability regimes for steady state and pulsed reactors

International Nuclear Information System (INIS)

Jardin, S.C.; Kessel, C.E.; Pomphrey, N.

1994-02-01

A tokamak reactor will operate at the maximum value of β≡2μ 0 /B 2 that is compatible with MHD stability. This value depends upon the plasma current and pressure profiles, the plasma shape and aspect ratio, and the location of nearby conducting structures. In addition, a steady state reactor will minimize its external current drive requirements and thus achieve its maximum economic benefit with a bootstrap fraction near one, I bs /I p ∼ 1, which constrains the product of the inverse aspect ratio and the plasma poloidal beta to be near unity, ε β p ∼ 1. An inductively driven pulsed reactor has different constraints set by the steady-state Ohm's law which relates the plasma temperature and density profiles to the parallel current density. We present the results obtained during the ARIES I, II/IV, and III and the PULSAR reactor studies where these quantities were optimized subject to different design philosophies. The ARIES-II/IV and ARIES-III designs are both in the second stability regime, but differ in requirements on the form of the profiles at the plasma edge, and in the location of the conducting wall. The relation between these, as well as new attractive MHD regimes not utilized in the ARIES or PULSAR studies is also discussed

Magnetohydrodynamic stability regimes for steady state and pulsed reactors

International Nuclear Information System (INIS)

Jardin, S.C.; Kessel, C.E.; Pomphrey, N.

1994-01-01

A tokamak reactor will operate at the maximum value of β≡2μ 0 left angle p right angle /B 2 that is compatible with magnetohydrodynamic (MHD) stability. This value depends on the plasma current and pressure profiles, the plasma shape and aspect ratio, and the location of nearby conducting structures. In addition, a steady state reactor will minimize its external current drive requirements and thus achieve its maximum economic benefit with a bootstrap fraction near unity, I BS /I P ∼1, which constrains the product of the inverse aspect ratio and the plasma poloidal β to be near unity, arepsilonβ P ∼1. An inductively driven pulsed reactor has different constraints set by the steady-state Ohm's law which relates the plasma temperature and density profiles to the parallel current density. We present the results obtained during ARIES I, II/IV, and III and PULSAR reactor studies where these quantities were optimized subject to different design philosophies. The ARIES-II/IV and ARIES-III designs are both in the second stability regime, but differ in requirements in the form of the profiles at the plasma edge, and in the location of the conducting wall. The relation between these, as well as new attractive MHD regimes not utilized in the ARIES or PULSAR studies, is also discussed. ((orig.))

Exploring Pulsars with Polestar

Science.gov (United States)

Cappallo, Rigel; Laycock, Silas; Christodoulou, Dimitris

2018-06-01

An X-ray pulsar (XRP) is a highly-magnetized neutron star (NS) that rotates while emitting beams of X-ray radiation produced primarily in the vicinity of its magnetic poles. If these beams happen to cross our line of sight and the NS’s spin and magnetic axes are not aligned, then our telescopes detect it as a periodically pulsating source. With the introduction of a new class of orbit-based observatories over the last quarter of a century the field of X-ray pulsar astronomy has seen an influx of high-resolution data. This windfall demands new models of pulsar behavior and emission geometry be created and subsequently fit to this high-quality data.We have written a model (Polestar) in Python 2.7.6 that mathematically represents a simplified XRP. The code has ten different, tunable geometric parameters that can be individually incorporated or suppressed. Any given XRP has a unique pulse profile which is often energy-dependent, and changes with different luminosity states. A change in luminosity coincides with a change in the system (e.g. a periodic Type-1 outburst is triggered following periastron passage, or the orientation of the decretion disk around the donor star has changed), and as such an increase in luminosity tends to produce an increase in complexity of the accompanying pulse profile. If a particular source in a low-luminosity state can be fit well with Polestar incorporating only a few parameters then an underlying geometry may be inferred. Further, if profiles from the same source in higher-luminosity states can be fit with the addition of only one or two additional parameters it will serve to further solidify current XRP theory (e.g. the emergence of fan-like emission patterns, or the vertical growth of the accretion column).Our initial fitting campaign was directed at the ~ 100 XRPs in the Small Magellanic Cloud. Polestar also includes an interactive slider GUI that allows the user to see in real time how changing the various profiles alter the

Low-frequency polarimetry of the millisecond pulsar PSR1937+214

Energy Technology Data Exchange (ETDEWEB)

Stinebring, D R [National Radio Astronomy Observatory, Charlottesville, VA (USA); Cordes, J M [Cornell Univ., Ithaca, NY (USA). Dept. of Astronomy; Cornell Univ., Ithaca, NY (USA). National Astronomy and Ionospheric Center)

1983-11-24

Polarization observations are reported at 431 MHz that have 4 ..mu..s time resolution and are free from the effects of interstellar dispersion. The interpulse polarization decreases towards lower frequencies, opposite in trend to the polarization of the main pulse and of most other pulsars. The position angles at the center of the main pulse and interpulse are approximately equal and the position angle gradients have the same sign, supporting a model in which the main pulse and interpulse are emitted above opposite magnetic poles.

Recycling behaviour during long pulse discharges after ICRF boronization in the HT-7 tokamak

International Nuclear Information System (INIS)

Huang, J.; Wan, B.N.; Li, J.G.; Gong, X.Z.; Zhang, X.D.; Wu, Z.W.; Zhou, Q.

2006-01-01

The evolution of recycling behaviour has been investigated during long pulse discharges in the HT-7 tokamak after ICRF boronization (C 2 B 10 H 12 ) using the H/(H+D) ratio and the edge recycling coefficient R. After boronization, impurity reduction is observed, attributed to the fresh boron film, but the recycling coefficient can exceed unity due to a large amount of hydrogen absorbed in the film, leading to an uncontrollable density rise and discharge termination. When the H/(H+D) ratio was reduced to less than 25%, the electron density was easily controlled. The longest discharge, up to 240 s with central electron temperature T e (0) of about 1.0 keV and central electron density n e (0) of 0.8 x 10 19 m -3 , was achieved following boronization. After many discharges the effectiveness of boron film was weakened, and the density rise was correlated with an increase in both carbon and oxygen radiation which limited the duration of long pulse discharges

Observation of bulk-ion heating in a tokamak plasma by application of positive and negative current pulses in TRIAM-1

Energy Technology Data Exchange (ETDEWEB)

Toi, K; Hiraki, N; Nakamura, K; Mitarai, O; Kawai, Y; Itoh, S [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics

1980-09-01

A positive of negative current pulse induced by a pulsed toroidal electric field much higher than the Dreicer field increases the bulk-ion temperature of the plasma centre two to three times, without macroscopic plasma destruction. The decay time of the raised ion temperature agrees well with the prediction from neoclassical transport theory. The magnitude of the positive current pulse is limited by violent current disruption, and that of the negative current by a lack of MHD equilibrium which is due to a marked reduction of the total plasma current. The relevant current-driven instabilities in the turbulent heating of a tokamak plasma, skin heating and inward transfer of the energy deposition in the skin layer are briefly discussed.

Fermi LAT Pulsed Detection of PSR J0737-3039A in the Double Pulsar System

Science.gov (United States)

Guillemot, L.; Kramer, M.; Johnson, T. J.; Craig, H. A.; Romani, R. W.; Venter, C.; Harding, A. K.; Ferdman, R. D.; Stairs, I. H.; Kerr, M.

2013-01-01

We report the Fermi Large Area Telescope discovery of gamma-ray pulsations from the 22.7 ms pulsar A in the double pulsar system J0737-3039A/B. This is the first mildly recycled millisecond pulsar (MSP) detected in the GeV domain. The 2.7 s companion object PSR J0737-3039B is not detected in gamma rays. PSR J0737-3039A is a faint gamma-ray emitter, so that its spectral properties are only weakly constrained; however, its measured efficiency is typical of other MSPs. The two peaks of the gamma-ray light curve are separated by roughly half a rotation and are well offset from the radio and X-ray emission, suggesting that the GeV radiation originates in a distinct part of the magnetosphere from the other types of emission. From the modeling of the radio and the gamma-ray emission profiles and the analysis of radio polarization data, we constrain the magnetic inclination alpha and the viewing angle zeta to be close to 90 deg., which is consistent with independent studies of the radio emission from PSR J0737-3039A. A small misalignment angle between the pulsar's spin axis and the system's orbital axis is therefore favored, supporting the hypothesis that pulsar B was formed in a nearly symmetric supernova explosion as has been discussed in the literature already.

Advanced tokamak burning plasma experiment

International Nuclear Information System (INIS)

Porkolab, M.; Bonoli, P.T.; Ramos, J.; Schultz, J.; Nevins, W.N.

2001-01-01

A new reduced size ITER-RC superconducting tokamak concept is proposed with the goals of studying burn physics either in an inductively driven standard tokamak (ST) mode of operation, or in a quasi-steady state advanced tokamak (AT) mode sustained by non-inductive means. This is achieved by reducing the radiation shield thickness protecting the superconducting magnet by 0.34 m relative to ITER and limiting the burn mode of operation to pulse lengths as allowed by the TF coil warming up to the current sharing temperature. High gain (Q≅10) burn physics studies in a reversed shear equilibrium, sustained by RF and NB current drive techniques, may be obtained. (author)

Ultra-long pulse operation using lower hybrid waves on the superconducting high field tokamak TRIAM-1M

International Nuclear Information System (INIS)

Moriyama, S.; Nakamura, Y.; Nagao, A.; Jotaki, E.; Nakamura, K.; Hiraki, N.; Itoh, S.

1990-01-01

Ultra-long pulse operation (>3 min) was achieved on the superconducting high field tokamak TRIAM-1M. In this operation, the plasma current was maintained with a relatively peaked current distribution by the 2.45 GHz radiofrequency power (P RF ≤ 35 kW) alone. A stationary plasma with a driven current of up to 35 kA and a line averaged electron density of up to 3x10 12 cm -3 was produced by precise plasma position and gas feed control. The extremely long discharge showed the interesting characteristics that the high temperatures of about 1 keV for the electrons and about 0.5 keV for the ions were kept almost constant during steady state current drive and that there was no impurity accumulation which could have a fatally adverse effect on steady state tokamak operation. (author). 16 refs, 17 figs

Building X-ray pulsar timing model without the use of radio parameters

Science.gov (United States)

Sun, Hai-feng; Sun, Xiong; Fang, Hai-yan; Shen, Li-rong; Cong, Shao-peng; Liu, Yan-ming; Li, Xiao-ping; Bao, Wei-min

2018-02-01

This paper develops a timing solution for the X-ray pulsar timing model without the use of the initial radio model parameters. First, we address the problem of phase ambiguities for the pre-fit residuals in the construction of pulsar timing model. To improve the estimation accuracy of the pulse time of arrival (TOA), we have deduced the general form of test statistics in Fourier transform, and discussed their estimation performances. Meanwhile, a fast maximum likelihood (FML) technique is presented to estimate the pulse TOA, which outperforms cross correlation (CC) estimator and exhibits a performance comparable with maximum likelihood (ML) estimator in spite of a much less reduced computational complexity. Depending on the strategy of the difference minimum of pre-fit residuals, we present an effective forced phase-connected technique to achieve initial model parameters. Then, we use the observations with the Rossi X-Ray Timing Explorer (RXTE) and X-ray pulsar navigation-I (XPNAV-1) satellites for experimental studies, and discuss main differences for the root mean square (RMS) residuals calculated with the X-ray and radio ephemerides. Finally, a chi-square value (CSV) of pulse profiles is presented as a complementary indicator to the RMS residuals for evaluating the model parameters. The results show that the proposed timing solution is valid and effective, and the obtained model parameters can be a reasonable alternative to the radio ephemeris.

RXTE observations of the Vela Pulsar: The pulsar rosetta stone

International Nuclear Information System (INIS)

Strickman, M.S.; Harding, A.K.; Gwinn, C.; McCulloch, P.; Moffett, D.

2001-01-01

We report on our analysis of a 274 ks observation of the Vela Pulsar with the Rossi X-Ray Timing Explorer (RXTE). The double-peaked, pulsed emission at 2-30 keV, which we had previously detected during a 93 ks observation, is confirmed with much improved statistics. There is now clear evidence, both in the spectrum and the light curve, that the emission in the RXTE band is a blend of two separate components. The spectrum of the harder component connects smoothly with the OSSE, COMPTEL and EGRET spectra and the peaks in the light curve are in phase coincidence with those of the high-energy light curve. The spectrum of the softer component is consistent with an extrapolation to the pulsed optical flux and the soft component of the second RXTE peak is in phase coincidence with the second optical peak. In addition, we see a peak in the 2-8 keV RXTE light curve at the radio peak phase

NuSTAR detection of 4s Hard X-ray Lags from the Accreting Pulsar GS 0834-430

DEFF Research Database (Denmark)

Bachetti, Matteo; Miyasaka, Hiromasa; Harrison, Fiona

2014-01-01

is consistent with that observed in many other magnetized accreting pulsars. We fail to detect cyclotron resonance scattering features in either phase-averaged nor phase-resolved spectra that would allow us to constrain the pulsar’s magnetic field. We detect a pulse period of ∼ 12.29 s in all energy bands....... The pulse profile can be modeled with a double Gaussian and shows a strong and smooth hard lag of up to 0.3 cycles in phase, or about 4s between the pulse at ∼ 3 and >∼ 30 keV. This is the first report of such a strong lag in high-mass X-ray binary (HMXB) pulsars. Previously reported lags have been...

Prospects for high-precision pulsar timing with the new Effelsberg PSRIX backend

Science.gov (United States)

Lazarus, P.; Karuppusamy, R.; Graikou, E.; Caballero, R. N.; Champion, D. J.; Lee, K. J.; Verbiest, J. P. W.; Kramer, M.

2016-05-01

The PSRIX backend is the primary pulsar timing instrument of the Effelsberg 100 m radio telescope since early 2011. This new ROACH-based system enables bandwidths up to 500 MHz to be recorded, significantly more than what was possible with its predecessor, the Effelsberg-Berkeley Pulsar Processor (EBPP). We review the first four years of PSRIX timing data for 33 pulsars collected as part of the monthly European Pulsar Timing Array (EPTA) observations. We describe the automated data analysis pipeline, COASTGUARD, that we developed to reduce these observations. We also introduce TOASTER, the EPTA timing data base, used to store timing results, processing information and observation metadata. Using these new tools, we measure the phase-averaged flux densities at 1.4 GHz of all 33 pulsars. For seven of these pulsars, our flux density measurements are the first values ever reported. For the other 26 pulsars, we compare our flux density measurements with previously published values. By comparing PSRIX data with EBPP data, we find an improvement of ˜2-5 times in signal-to-noise ratio, which translates to an increase of ˜2-5 times in pulse time-of-arrival (TOA) precision. We show that such an improvement in TOA precision will improve the sensitivity to the stochastic gravitational wave background. Finally, we showcase the flexibility of the new PSRIX backend by observing several millisecond-period pulsars (MSPs) at 5 and 9 GHz. Motivated by our detections, we discuss the potential for complementing existing pulsar timing array data sets with MSP monitoring campaigns at these higher frequencies.

X-RAY PULSATIONS FROM THE RADIO-QUIET GAMMA-RAY PULSAR IN CTA 1

International Nuclear Information System (INIS)

Caraveo, P. A.; De Luca, A.; Marelli, M.; Bignami, G. F.; Ray, P. S.; Saz Parkinson, P. M.; Kanbach, G.

2010-01-01

Prompted by the Fermi-LAT discovery of a radio-quiet gamma-ray pulsar inside the CTA 1 supernova remnant, we obtained a 130 ks XMM-Newton observation to assess the timing behavior of this pulsar. Exploiting both the unprecedented photon harvest and the contemporary Fermi-LAT timing measurements, a 4.7σ single-peak pulsation is detected, making PSR J0007+7303 the second example, after Geminga, of a radio-quiet gamma-ray pulsar also seen to pulsate in X-rays. Phase-resolved spectroscopy shows that the off-pulse portion of the light curve is dominated by a power-law, non-thermal spectrum, while the X-ray peak emission appears to be mainly of thermal origin, probably from a polar cap heated by magnetospheric return currents, pointing to a hot spot varying throughout the pulsar rotation.

A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope

International Nuclear Information System (INIS)

Dumora, D.; Grondin, M.H.; Guillemot, L.; Lemoine-Goumard, M.; Lovellette, M.N.; Parent, D.; Smith, D.A.; Abdo, A.A.; Chekhtman, A.; Dermer, C.D.; Grove, J.E.; Johnson, W.N.; Makeev, A.; Ray, P.S.; Strickman, M.S.; Wood, K.S.; Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Blandford, R.D.; Bloom, E.D.; Borgland, A.W.; Cameron, R.A.; Charles, E.; Chiang, J.; Claus, R.; Digel, S.W.; Silva, E.D.E.; Drell, P.S.; Dubois, R.; Edmonds, Y.; Focke, W.B.; Funk, S.; Glanzman, T.; Godfrey, G.; Hayashida, M.; Johannesson, G.; Kocian, M.L.; Lande, J.; Madejski, G.M.; Michelson, P.F.; Mitthumsiri, W.; Monzani, M.E.; Moskalenko, I.V.; Murgia, S.; Nolan, P.L.; Paneque, D.; Panetta, J.H.; Reimer, A.; Reimer, O.; Rochester, L.S.; Romani, R.W.; Tajima, H.; Tanaka, T.; Thayer, J.B.; Thayer, J.G.; Tramacere, A.; Uchiyama, Y.; Usher, T.L.; Van Etten, A.; Waite, A.P.; Wang, P.; Watters, K.; Atwood, W.B.; Dormody, M.; Johnson, R.P.; Porter, T.A.; Sadrozinski, H.F.W.; Schalk, T.L.; Thorsett, S.E.; Ziegler, M.; Axelsson, M.; Carlson, P.; Conrad, J.; Meurer, C.; Ryde, F.; Ylinen, T.; Axelsson, M.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Kuss, M.; Latronico, L.; Omodei, N.; Pesce-Rollins, M.; Razzano, M.; Sgro, C.; Spandre, G.; Ballet, J.; Casandjian, J.M.; Grenier, I.A.; Starck, J.L.

2009-01-01

Pulsars are born with sub-second spin periods and slow by electromagnetic braking for several tens of millions of years, when detectable radiation ceases. A second life can occur for neutron stars in binary systems. They can acquire mass and angular momentum from their companions, to be spun up to millisecond periods and begin radiating again. We searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars (MSPs) outside of globular clusters, using rotation parameters from radio telescopes. Strong gamma-ray pulsations were detected for eight MSPs. The gamma-ray pulse profiles and spectral properties resemble those of young gamma-ray pulsars. The basic emission mechanism seems to be the same for MSPs and young pulsars, with the emission originating in regions far from the neutron star surface. (authors)

Pulsars at Parkes

OpenAIRE

Manchester, R. N.

2012-01-01

The first pulsar observations were made at Parkes on March 8, 1968, just 13 days after the publication of the discovery paper by Hewish and Bell. Since then, Parkes has become the world's most successful pulsar search machine, discovering nearly two thirds of the known pulsars, among them many highly significant objects. It has also led the world in pulsar polarisation and timing studies. In this talk I will review the highlights of pulsar work at Parkes from those 1968 observations to about ...

Pulsar wind model for the spin-down behavior of intermittent pulsars

Energy Technology Data Exchange (ETDEWEB)

Li, L.; Tong, H.; Yan, W. M.; Yuan, J. P.; Wang, N. [Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011 (China); Xu, R. X., E-mail: tonghao@xao.ac.cn [School of Physics, Peking University, Beijing (China)

2014-06-10

Intermittent pulsars are part-time radio pulsars. They have higher slow down rates in the on state (radio-loud) than in the off state (radio-quiet). This gives evidence that particle wind may play an important role in pulsar spindown. The effect of particle acceleration is included in modeling the rotational energy loss rate of the neutron star. Applying the pulsar wind model to the three intermittent pulsars (PSR B1931+24, PSR J1841–0500, and PSR J1832+0029) allows their magnetic fields and inclination angles to be calculated simultaneously. The theoretical braking indices of intermittent pulsars are also given. In the pulsar wind model, the density of the particle wind can always be the Goldreich-Julian density. This may ensure that different on states of intermittent pulsars are stable. The duty cycle of particle wind can be determined from timing observations. It is consistent with the duty cycle of the on state. Inclination angle and braking index observations of intermittent pulsars may help to test different models of particle acceleration. At present, the inverse Compton scattering induced space charge limited flow with field saturation model can be ruled out.

FERMI LAT PULSED DETECTION OF PSR J0737-3039A IN THE DOUBLE PULSAR SYSTEM

Energy Technology Data Exchange (ETDEWEB)

Guillemot, L.; Kramer, M. [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Johnson, T. J. [National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001 (United States); Craig, H. A.; Romani, R. W.; Kerr, M. [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States); Venter, C. [Centre for Space Research, North-West University, Potchefstroom Campus, Private Bag X6001, 2520 Potchefstroom (South Africa); Harding, A. K. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Ferdman, R. D. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, M13 9PL (United Kingdom); Stairs, I. H., E-mail: guillemo@mpifr-bonn.mpg.de [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1 (Canada)

2013-05-10

We report the Fermi Large Area Telescope discovery of {gamma}-ray pulsations from the 22.7 ms pulsar A in the double pulsar system J0737-3039A/B. This is the first mildly recycled millisecond pulsar (MSP) detected in the GeV domain. The 2.7 s companion object PSR J0737-3039B is not detected in {gamma} rays. PSR J0737-3039A is a faint {gamma}-ray emitter, so that its spectral properties are only weakly constrained; however, its measured efficiency is typical of other MSPs. The two peaks of the {gamma}-ray light curve are separated by roughly half a rotation and are well offset from the radio and X-ray emission, suggesting that the GeV radiation originates in a distinct part of the magnetosphere from the other types of emission. From the modeling of the radio and the {gamma}-ray emission profiles and the analysis of radio polarization data, we constrain the magnetic inclination {alpha} and the viewing angle {zeta} to be close to 90 Degree-Sign , which is consistent with independent studies of the radio emission from PSR J0737-3039A. A small misalignment angle between the pulsar's spin axis and the system's orbital axis is therefore favored, supporting the hypothesis that pulsar B was formed in a nearly symmetric supernova explosion as has been discussed in the literature already.

Discovery of Radio Pulsations from the X-ray Pulsar JO205+6449 in Supernova Remnant 3C58 with the Green Bank Telescope

Science.gov (United States)

Camilo, F.; Stairs, I. H.; Lorimer, D. R.; Backer, D. C.; Ransom, S. M.; Klein, B.; Wielebinski, R.; Kramer, M.; McLaughlin, M. A.; Arzoumanian, Z.;

Chandra Phase-resolved Spectroscopy of the High Magnetic Field Pulsar B1509−58

Energy Technology Data Exchange (ETDEWEB)

Hu, Chin-Ping; Ng, C.-Y. [Department of Physics, The University of Hong Kong, Pokfulam Road (Hong Kong); Takata, J. [School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei (China); Shannon, R. M. [International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102 (Australia); Johnston, S., E-mail: cphu@hku.hk, E-mail: ncy@bohr.physics.hku.hk [CSIRO Astronomy and Space Science, Australia Telescope National Facility, Box 76, Epping, NSW 1710 (Australia)

2017-04-01

We report on a timing and spectral analysis of the young, high magnetic field rotation-powered pulsar (RPP) B1509−58 using Chandra continuous-clocking mode observation. The pulsar’s X-ray light curve can be fit by the two Gaussian components and the pulsed fraction shows moderate energy dependence over the Chandra band. The pulsed X-ray spectrum is well described by a power law with a photon index 1.16(4), which is harder than the values measured with RXTE /PCA and NuSTAR . This result supports the log-parabolic model for the broadband X-ray spectrum. With the unprecedented angular resolution of Chandra , we clearly identified off-pulse X-ray emission from the pulsar, and its spectrum is best fit by a power law plus blackbody model. The latter component has a temperature of ∼0.14 keV with a bolometric luminosity comparable to the luminosities of other young and high magnetic field RPPs, and it lies between the temperature of magnetars and typical RPPs. In addition, we found that the nonthermal X-ray emission of PSR B1509−58 is significantly softer in the off-pulse phase than in the pulsed phase, with the photon index varying between 1.0 and 1.8 and anticorrelated with the flux. This is similar to the behavior of three other young pulsars. We interpreted it as different contributions of pair-creation processes at different altitudes from the neutron star surface according to the outer-gap model.

Are PSR 0656+14, PSR 0950+08, and PSR 1822-09 gamma ray pulsars?

Science.gov (United States)

Brown, Lawrence E.; Hartmann, Dieter H.

1993-01-01

The possible discovery of three new gamma-ray pulsars PSR 0656+14, PSR 0950+08, and PSR 1822-09 (Ma, Lu, Yu, and Young, 1993) in data obtained with the COS-B experiment is reinvestigated using a refined technique for pulsar light curve analysis. The results of this study do not confirm the previously claimed gamma-ray pulsar nature of any of these pulsars. Even when using the standard epoch folding technique in conjunction with energy-dependent acceptance cones, we do not detect pulsed gamma-ray emission from these sources. We suspect that insufficient position accuracy is the cause for the discrepancy between our results and those of Ma et al. (1993). We do not rule out that any one of the three candidates, or all of them, is in fact a gamma-ray pulsar, but their spin properties must differ from those derived by Ma et al. (1993). More work is needed to determine the correct high-energy properties of these three sources.

The Bursting Pulsar GRO J1744-28: the Slowest Transitional Pulsar?

Science.gov (United States)

Court, J. M. C.; Altamirano, D.; Sanna, A.

2018-04-01

GRO J1744-28 (the Bursting Pulsar) is a neutron star LMXB which shows highly structured X-ray variability near the end of its X-ray outbursts. In this letter we show that this variability is analogous to that seen in Transitional Millisecond Pulsars such as PSR J1023+0038: `missing link' systems consisting of a pulsar nearing the end of its recycling phase. As such, we show that the Bursting Pulsar may also be associated with this class of objects. We discuss the implications of this scenario; in particular, we discuss the fact that the Bursting Pulsar has a significantly higher spin period and magnetic field than any other known Transitional Pulsar. If the Bursting Pulsar is indeed transitional, then this source opens a new window of oppurtunity to test our understanding of these systems in an entirely unexplored physical regime.

Deep Chandra Survey of the Small Magellanic Cloud. II. Timing Analysis of X-Ray Pulsars

Energy Technology Data Exchange (ETDEWEB)

Hong, JaeSub; Antoniou, Vallia; Zezas, Andreas; Drake, Jeremy J.; Plucinsky, Paul P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Haberl, Frank [Max-Planck-Institut für extraterrestrische Physik, Giessenbach straße, D-85748 Garching (Germany); Sasaki, Manami [Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstrasse 7, 96049 Bamberg (Germany); Laycock, Silas, E-mail: jaesub@head.cfa.harvard.edu [Department of Physics, University of Massachusetts Lowell, MA 01854 (United States)

2017-09-20

We report the timing analysis results of X-ray pulsars from a recent deep Chandra survey of the Small Magellanic Cloud (SMC). We analyzed a total exposure of 1.4 Ms from 31 observations over a 1.2 deg{sup 2} region in the SMC under a Chandra X-ray Visionary Program. Using the Lomb–Scargle and epoch-folding techniques, we detected periodic modulations from 20 pulsars and a new candidate pulsar. The survey also covered 11 other pulsars with no clear sign of periodic modulation. The 0.5–8 keV X-ray luminosity ( L {sub X} ) of the pulsars ranges from 10{sup 34} to 10{sup 37} erg s{sup −1} at 60 kpc. All of the Chandra sources with L {sub X} ≳ 4 × 10{sup 35} erg s{sup −1} exhibit X-ray pulsations. The X-ray spectra of the SMC pulsars (and high-mass X-ray binaries) are in general harder than those of the SMC field population. All but SXP 8.02 can be fitted by an absorbed power-law model with a photon index of Γ ≲ 1.5. The X-ray spectrum of the known magnetar SXP 8.02 is better fitted with a two-temperature blackbody model. Newly measured pulsation periods of SXP 51.0, SXP 214, and SXP 701, are significantly different from the previous XMM-Newton and RXTE measurements. This survey provides a rich data set for energy-dependent pulse profile modeling. Six pulsars show an almost eclipse-like dip in the pulse profile. Phase-resolved spectral analysis reveals diverse spectral variations during pulsation cycles: e.g., for an absorbed power-law model, some exhibit an (anti)-correlation between absorption and X-ray flux, while others show more intrinsic spectral variation (i.e., changes in photon indices).

ngVLA Key Science Goal 4: Using Pulsars in the Galactic Center as Fundamental Tests of Gravity

Science.gov (United States)

Bower, Geoffrey C.; Chatterjee, Shami; Cordes, James; Demorest, Paul; Dexter, Jason; Kramer, Michael; Lazio, Joseph; Ransom, Scott; Wharton, Robert; ngVLA Science Working Group 4

2018-01-01

Pulsars in the Galactic Center (GC) are important probes of general relativity (GR), star formation, stellar dynamics, stellar evolution, and the interstellar medium. A pulsar in orbit around the massive black hole in the GC, Sgr A*, has the power to provide a high-precision measurement of the black hole mass and spin in a unique regime of GR. It is sufficient to find and time a normal, slowly rotating pulsar in a reasonable orbit, in order to measure the mass of Sgr A* with a precision of 1 solar mass, to test the cosmic censorship conjecture to a precision of 0.1%, and to test the no-hair theorem to a precision of 1%. The pulsar population in the GC on scales from the inner parsec to the edge of the Central Molecular Zone (250 parsecs in diameter) can provide fresh insight into the complex processes at work in this region: the characteristic age distribution of the discovered pulsars will give insight into the star formation history; millisecond pulsars can be used as acceleratormeters to probe the local gravitational potential; the observed dispersion and scattering measures (and their variability) will allow us to probe the distribution, clumpiness and other properties of the central interstellar medium, including characterization of the central magnetic field using Faraday rotation. Proper motions of young pulsars can be used to point back to regions of recent star formation and/or supernova remnants.Despite years of searching, only a handful of pulsars in the central 0.5 degrees are known. This is likely the result of strong interstellar scattering along the line of sight, which broadens individual pulses to greater width than the pulse period. Scattering effects decline as wavelength to the fourth power, implying that we require observation at higher frequencies than are typical for typical pulsar searches. The characteristic steep spectrum of pulsars, however, implies the need for greater instrumental sensitivity at higher frequencies in order to detect and

Large aspect ratio tokamak study

International Nuclear Information System (INIS)

Reid, R.L.; Holmes, J.A.; Houlberg, W.A.; Peng, Y.K.M.; Strickler, D.J.; Brown, T.G.; Sardella, C.; Wiseman, G.W.

1979-01-01

The Large Aspect Ratio Tokamak Study (LARTS) investigated the potential for producing a viable long burn tokamak reactor through enhanced volt-second capability of the ohmic heating transformer by employing high aspect ratio designs. The plasma physics, engineering, and economic implications of high aspect ratio tokamaks were accessed in the context of extended burn operation. Plasma startup and burn parameters were addressed using a one-dimensional transport code. The pulsed electrical power requirements for the poloidal field system, which have a major impact on reactor economics, were minimized by optimizing the field in the ohmic heating coil and the wave shape of the ohmic heating discharge. A high aspect ratio reference reactor was chosen and configured

Discovery of an Energetic Pulsar Associated with SNR G76.9+1.0

Science.gov (United States)

Arzoumanian, Zaven; Gotthelf, E. V.; Ransom, S. M.; Safi-Harb, S.; Kothes, R.; Landecker, T. L.

2012-01-01

We report the discovery of PSR J2022-pulsar in the supernova remnant G76.9+i.0, in observations with the Chandra X-ray telescope, the Robert C. Byrd Green Bank Radio Telescope, and the Rossi X-ray Timing Explorer (RXTE). The pulsar's spin-down rate implies a rotation-powered luminosity E = 1.2 X 10(exp 38) erg/s, a surface dipole magnetic field strength B(sub S), = 1.0 X 10(exp 12) G, and a characteristic age of 8.9 kyr. PSR J2022+3842 is thus the second-most energetic Galactic pulsar known, after the Crab, as well as the most rapidly-rotating young, radio-bright pulsar known. The radio pulsations are highly dispersed and broadened by interstellar scattering, and we find that a large (delta f/f approximates 1.9 x 10(exp -6)) spin glitch must have occurred between our discovery and confirmation observations. The X-ray pulses are narrow (0.06 cycles FWHM) and visible up to 20 keV, consistent with magnetospheric emission from a rotation-powered pulsar. The Chandra X-ray image identifies the pulsar with a hard, unresolved source at the midpoint of the double-lobed radio morphology of G76.9+ 1.0 and embedded within faint, compact X-ray nebulosity. The spatial relationship of the X-ray and radio emissions is remarkably similar to extended structure seen around the Vela pulsar. The combined Chandra and RXTE pulsar spectrum is well-fitted by an absorbed power-law model with column density N(sub H) = (1.7 +/- 0.3) x 10(exp 22) / sq cm and photon index Gamma = 1.0 +/- 0.2; it implies that the Chandra point-source flux is virtually 100% pulsed. For a distance of 10 kpc, the X-ray luminosity of PSR J2022+3842 is L(sub x){2-1O keV) = 7.0 x 10(exp 33) erg/s. Despite being extraordinarily energetic, PSR J2022+3842 lacks a bright X-ray wind nebula and has an unusually low conversion efficiency of spin-down power to X-ray luminosity, Lx/E = 5.9 X 10(exp-5).

THE NANOGRAV NINE-YEAR DATA SET: EXCESS NOISE IN MILLISECOND PULSAR ARRIVAL TIMES

Energy Technology Data Exchange (ETDEWEB)

Lam, M. T.; Jones, M. L.; McLaughlin, M. A.; Pennucci, T. T. [Department of Physics, West Virginia University, White Hall, Morgantown, WV 26506 (United States); Cordes, J. M.; Chatterjee, S. [Department of Astronomy and Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14853 (United States); Arzoumanian, Z. [Center for Research and Exploration in Space Science and Technology and X-Ray Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States); Crowter, K.; Fonseca, E.; Gonzalez, M. E. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Demorest, P. B. [National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM, 87801 (United States); Dolch, T. [Department of Physics, Hillsdale College, 33 E. College Street, Hillsdale, MI 49242 (United States); Ellis, J. A [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA, 91109 (United States); Ferdman, R. D. [Department of Physics, McGill University, 3600 rue Universite, Montreal, QC H3A 2T8 (Canada); Jones, G. [Department of Physics, Columbia University, 550 W. 120th Street, New York, NY 10027 (United States); Levin, L. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL (United Kingdom); Madison, D. R.; Ransom, S. M. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Nice, D. J. [Department of Physics, Lafayette College, Easton, PA 18042 (United States); Shannon, R. M., E-mail: michael.lam@mail.wvu.edu [CSIRO Astronomy and Space Science, Australia Telescope National Facility, Box 76, Epping NSW 1710 (Australia); and others

2017-01-01

Gravitational wave (GW) astronomy using a pulsar timing array requires high-quality millisecond pulsars (MSPs), correctable interstellar propagation delays, and high-precision measurements of pulse times of arrival. Here we identify noise in timing residuals that exceeds that predicted for arrival time estimation for MSPs observed by the North American Nanohertz Observatory for Gravitational Waves. We characterize the excess noise using variance and structure function analyses. We find that 26 out of 37 pulsars show inconsistencies with a white-noise-only model based on the short timescale analysis of each pulsar, and we demonstrate that the excess noise has a red power spectrum for 15 pulsars. We also decompose the excess noise into chromatic (radio-frequency-dependent) and achromatic components. Associating the achromatic red-noise component with spin noise and including additional power-spectrum-based estimates from the literature, we estimate a scaling law in terms of spin parameters (frequency and frequency derivative) and data-span length and compare it to the scaling law of Shannon and Cordes. We briefly discuss our results in terms of detection of GWs at nanohertz frequencies.

Abrupt acceleration of a 'cold' ultrarelativistic wind from the Crab pulsar.

Science.gov (United States)

Aharonian, F A; Bogovalov, S V; Khangulyan, D

2012-02-15

Pulsars are thought to eject electron-positron winds that energize the surrounding environment, with the formation of a pulsar wind nebula. The pulsar wind originates close to the light cylinder, the surface at which the pulsar co-rotation velocity equals the speed of light, and carries away much of the rotational energy lost by the pulsar. Initially the wind is dominated by electromagnetic energy (Poynting flux) but later this is converted to the kinetic energy of bulk motion. It is unclear exactly where this takes place and to what speed the wind is accelerated. Although some preferred models imply a gradual acceleration over the entire distance from the magnetosphere to the point at which the wind terminates, a rapid acceleration close to the light cylinder cannot be excluded. Here we report that the recent observations of pulsed, very high-energy γ-ray emission from the Crab pulsar are explained by the presence of a cold (in the sense of the low energy of the electrons in the frame of the moving plasma) ultrarelativistic wind dominated by kinetic energy. The conversion of the Poynting flux to kinetic energy should take place abruptly in the narrow cylindrical zone of radius between 20 and 50 light-cylinder radii centred on the axis of rotation of the pulsar, and should accelerate the wind to a Lorentz factor of (0.5-1.0) × 10(6). Although the ultrarelativistic nature of the wind does support the general model of pulsars, the requirement of the very high acceleration of the wind in a narrow zone not far from the light cylinder challenges current models.

Experimental Constraints on γ-Ray Pulsar Gap Models and the Pulsar GeV to Pulsar Wind Nebula TeV Connection

Science.gov (United States)

Abeysekara, A. U.; Linnemann, J. T.

2015-05-01

The pulsar emission mechanism in the gamma ray energy band is poorly understood. Currently, there are several models under discussion in the pulsar community. These models can be constrained by studying the collective properties of a sample of pulsars, which became possible with the large sample of gamma ray pulsars discovered by the Fermi Large Area Telescope. In this paper we develop a new experimental multi-wavelength technique to determine the beaming factor ≤ft( {{f}{Ω }} \\right) dependance on spin-down luminosity of a set of GeV pulsars. This technique requires three input parameters: pulsar spin-down luminosity, pulsar phase-averaged GeV flux, and TeV or X-ray flux from the associated pulsar wind nebula (PWN). The analysis presented in this paper uses the PWN TeV flux measurements to study the correlation between {{f}{Ω }} and \\dot{E}. The measured correlation has some features that favor the Outer Gap model over the Polar Cap, Slot Gap, and One Pole Caustic models for pulsar emission in the energy range of 0.1-100 GeV, but one must keep in mind that these simulated models failed to explain many of the most important pulsar population characteristics. A tight correlation between the pulsar GeV emission and PWN TeV emission was also observed, which suggests the possibility of a linear relationship between the two emission mechanisms. In this paper we also discuss a possible mechanism to explain this correlation.

Microwave tokamak experiment (MTX) first year of operation and future plans

International Nuclear Information System (INIS)

Jackson, M.C.

1989-01-01

The Microwave Tokamak Experiment (MTX) at Lawrence Livermore National Laboratory (LLNL) began plasma operations in November 1988, and our main goal is the study of electron-cyclotron heating (ECH) in plasma discharges. The MTX tokamak was relocated from the Massachusetts Institute of Technology (MIT), and we have re-created plasma parameters that are similar to those generated while the tokamak was at MIT. After stable ohmic operation was achieved, single-pulse FEL heating experiments began. During this phase, the FEL operated at low power levels on the way to its ultimate goal of 2 GW and 140 GHz with a 30-ns pulse length. We have developed a number of new diagnostics to measure these fast FEL pulses and the resulting plasma effects. In this paper, we present results that show the correlation of MTX data with MIT data, some of the operational modifications and procedures used, results to date from preliminary tokamak operations with the FEL, and our near-term operational plans. 7 refs., 8 figs., 1 tab

Efficiency of Synchrotron Radiation from Rotation-powered Pulsars

Energy Technology Data Exchange (ETDEWEB)

Kisaka, Shota [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa, 252-5258 (Japan); Tanaka, Shuta J., E-mail: kisaka@phys.aoyama.ac.jp, E-mail: sjtanaka@center.konan-u.ac.jp [Department of Physics, Konan University, Kobe, Hyogo, 658-8501 (Japan)

2017-03-01

Synchrotron radiation is widely considered to be the origin of the pulsed non-thermal emissions from rotation-powered pulsars in optical and X-ray bands. In this paper, we study the synchrotron radiation emitted by the created electron and positron pairs in the pulsar magnetosphere to constrain the energy conversion efficiency from the Poynting flux to the particle energy flux. We model two pair creation processes, two-photon collision, which efficiently works in young γ -ray pulsars (≲10{sup 6} year), and magnetic pair creation, which is the dominant process to supply pairs in old pulsars (≳10{sup 6} year). Using the analytical model, we derive the maximum synchrotron luminosity as a function of the energy conversion efficiency. From the comparison with observations, we find that the energy conversion efficiency to the accelerated particles should be an order of unity in the magnetosphere, even though we make a number of the optimistic assumptions to enlarge the synchrotron luminosity. In order to explain the luminosity of the non-thermal X-ray/optical emission from pulsars with low spin-down luminosity L {sub sd} ≲ 10{sup 34} erg s{sup −1}, non-dipole magnetic field components should be dominant at the emission region. For the γ -ray pulsars with L {sub sd} ≲ 10{sup 35} erg s{sup −1}, observed γ -ray to X-ray and optical flux ratios are much higher than the flux ratio between curvature and the synchrotron radiations. We discuss some possibilities such as the coexistence of multiple accelerators in the magnetosphere as suggested from the recent numerical simulation results. The obtained maximum luminosity would be useful to select observational targets in X-ray and optical bands.

NuSTAR DETECTION OF HARD X-RAY PHASE LAGS FROM THE ACCRETING PULSAR GS 0834–430

Energy Technology Data Exchange (ETDEWEB)

Miyasaka, Hiromasa; Harrison, Fiona A.; Fürst, Felix; Bellm, Eric C.; Grefenstette, Brian W.; Madsen, Kristin K.; Walton, Dominic J. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Bachetti, Matteo; Barret, Didier [Université de Toulouse, UPS-OMP, IRAP, F-31400 Toulouse (France); Boggs, Steven E.; Craig, William W.; Tomsick, John A. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Chakrabarty, Deepto [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Chenevez, Jerome; Christensen, Finn E. [DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); Hailey, Charles J. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Natalucci, Lorenzo [Istituto di Astrofisica e Planetologia Spaziali, INAF, Via Fosso del Cavaliere 100, Roma I-00133 (Italy); Pottschmidt, Katja [CRESST, UMBC, and NASA GSFC, Code 661, Greenbelt, MD 20771 (United States); Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Wilms, Jörn, E-mail: miyasaka@srl.caltech.edu [Dr. Karl-Remeis-Sternwarte and ECAP, Sternwartstr. 7, D-96049 Bamberg (Germany); and others

2013-09-20

The Nuclear Spectroscopic Telescope Array hard X-ray telescope observed the transient Be/X-ray binary GS 0834–430 during its 2012 outburst—the first active state of this system observed in the past 19 yr. We performed timing and spectral analysis and measured the X-ray spectrum between 3-79 keV with high statistical significance. We find the phase-averaged spectrum to be consistent with that observed in many other magnetized, accreting pulsars. We fail to detect cyclotron resonance scattering features that would allow us to constrain the pulsar's magnetic field in either phase-averaged or phase-resolved spectra. Timing analysis shows a clearly detected pulse period of ∼12.29 s in all energy bands. The pulse profiles show a strong, energy-dependent hard phase lag of up to 0.3 cycles in phase, or about 4 s. Such dramatic energy-dependent lags in the pulse profile have never before been reported in high-mass X-ray binary pulsars. Previously reported lags have been significantly smaller in phase and restricted to low energies (E < 10 keV). We investigate the possible mechanisms that might produce this energy-dependent pulse phase shift. We find the most likely explanation for this effect is a complex beam geometry.

Jumping the energetics queue: Modulation of pulsar signals by extraterrestrial civilizations

Science.gov (United States)

Chennamangalam, Jayanth; Siemion, Andrew P. V.; Lorimer, D. R.; Werthimer, Dan

2015-01-01

It has been speculated that technological civilizations evolve along an energy consumption scale first formulated by Kardashev, ranging from human-like civilizations that consume energy at a rate of ∼1019 erg s-1 to hypothetical highly advanced civilizations that can consume ∼1044 erg s-1. Since the transmission power of a beacon a civilization can build depends on the energy it possesses, to make it bright enough to be seen across the Galaxy would require high technological advancement. In this paper, we discuss the possibility of a civilization using naturally-occurring radio transmitters - specifically, radio pulsars - to overcome the Kardashev limit of their developmental stage and transmit super-Kardashev power. This is achieved by the use of a modulator situated around a pulsar, that modulates the pulsar signal, encoding information onto its natural emission. We discuss a simple modulation model using pulse nulling and considerations for detecting such a signal. We find that a pulsar with a nulling modulator will exhibit an excess of thermal emission peaking in the ultraviolet during its null phases, revealing the existence of a modulator.

Binary and Millisecond Pulsars

Directory of Open Access Journals (Sweden)

Lorimer Duncan R.

2008-11-01

Full Text Available We review the main properties, demographics and applications of binary and millisecond radio pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1800. There are now 83 binary and millisecond pulsars associated with the disk of our Galaxy, and a further 140 pulsars in 26 of the Galactic globular clusters. Recent highlights include the discovery of the young relativistic binary system PSR J1906+0746, a rejuvination in globular cluster pulsar research including growing numbers of pulsars with masses in excess of 1.5M_⊙, a precise measurement of relativistic spin precession in the double pulsar system and a Galactic millisecond pulsar in an eccentric (e = 0.44 orbit around an unevolved companion.

Synchronous x-ray and radio mode switches: a rapid global transformation of the pulsar magnetosphere.

Science.gov (United States)

Hermsen, W; Hessels, J W T; Kuiper, L; van Leeuwen, J; Mitra, D; de Plaa, J; Rankin, J M; Stappers, B W; Wright, G A E; Basu, R; Alexov, A; Coenen, T; Grießmeier, J-M; Hassall, T E; Karastergiou, A; Keane, E; Kondratiev, V I; Kramer, M; Kuniyoshi, M; Noutsos, A; Serylak, M; Pilia, M; Sobey, C; Weltevrede, P; Zagkouris, K; Asgekar, A; Avruch, I M; Batejat, F; Bell, M E; Bell, M R; Bentum, M J; Bernardi, G; Best, P; Bîrzan, L; Bonafede, A; Breitling, F; Broderick, J; Brüggen, M; Butcher, H R; Ciardi, B; Duscha, S; Eislöffel, J; Falcke, H; Fender, R; Ferrari, C; Frieswijk, W; Garrett, M A; de Gasperin, F; de Geus, E; Gunst, A W; Heald, G; Hoeft, M; Horneffer, A; Iacobelli, M; Kuper, G; Maat, P; Macario, G; Markoff, S; McKean, J P; Mevius, M; Miller-Jones, J C A; Morganti, R; Munk, H; Orrú, E; Paas, H; Pandey-Pommier, M; Pandey, V N; Pizzo, R; Polatidis, A G; Rawlings, S; Reich, W; Röttgering, H; Scaife, A M M; Schoenmakers, A; Shulevski, A; Sluman, J; Steinmetz, M; Tagger, M; Tang, Y; Tasse, C; ter Veen, S; Vermeulen, R; van de Brink, R H; van Weeren, R J; Wijers, R A M J; Wise, M W; Wucknitz, O; Yatawatta, S; Zarka, P

2013-01-25

Pulsars emit from low-frequency radio waves up to high-energy gamma-rays, generated anywhere from the stellar surface out to the edge of the magnetosphere. Detecting correlated mode changes across the electromagnetic spectrum is therefore key to understanding the physical relationship among the emission sites. Through simultaneous observations, we detected synchronous switching in the radio and x-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio-"bright" mode, the x-rays show only an unpulsed, nonthermal component. Conversely, when the pulsar is in a radio-"quiet" mode, the x-ray luminosity more than doubles and a 100% pulsed thermal component is observed along with the nonthermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories.

Swings between rotation and accretion power in a binary millisecond pulsar.

Science.gov (United States)

Papitto, A; Ferrigno, C; Bozzo, E; Rea, N; Pavan, L; Burderi, L; Burgay, M; Campana, S; Di Salvo, T; Falanga, M; Filipović, M D; Freire, P C C; Hessels, J W T; Possenti, A; Ransom, S M; Riggio, A; Romano, P; Sarkissian, J M; Stairs, I H; Stella, L; Torres, D F; Wieringa, M H; Wong, G F

2013-09-26

It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron star's rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales.

The design of the KSTAR tokamak

International Nuclear Information System (INIS)

Lee, G.S.; Kim, J.; Hwang, S.M.

1999-01-01

The Korea superconducting tokamak advanced research (KSTAR) project is the major effort of the Korean national fusion program (KNFP) to develop a steady-state-capable advanced superconducting tokamak to establish a scientific and technological basis for an attractive fusion reactor. Major parameters of the tokamak are: major radius 1.8 m, minor radius 0.5 m, toroidal field 3.5 Tesla, and plasma current 2 MA with a strongly shaped plasma cross-section and double-null divertor. The initial pulse length provided by the poloidal magnet system is 20 s, but the pulse length can be increased to 300 s through non-inductive current drive. The plasma heating and current drive system consists of neutral beam, ion cyclotron waves, lower hybrid waves, and electron-cyclotron waves for flexible profile control. A comprehensive set of diagnostics is planned for plasma control and performance evaluation and physics understanding. The project has completed its conceptual design phase and moved to the engineering design phase. The target date of the first plasma is set for year 2002. (orig.)

DETECTION OF POLARIZED QUASI-PERIODIC MICROSTRUCTURE EMISSION IN MILLISECOND PULSARS

Energy Technology Data Exchange (ETDEWEB)

De, Kishalay; Sharma, Prateek [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Gupta, Yashwant, E-mail: kde@caltech.edu [National Centre for Radio Astrophysics, TIFR, Pune University Campus, Post Bag 3, Pune 411007 (India)

2016-12-10

Microstructure emission, involving short timescale, often quasi-periodic, intensity fluctuations in subpulse emission, is well known in normal period pulsars. In this Letter, we present the first detections of quasi-periodic microstructure emission from millisecond pulsars (MSPs), from Giant Metrewave Radio Telescope observations of two MSPs at 325 and 610 MHz. Similar to the characteristics of microstructure observed in normal period pulsars, we find that these features are often highly polarized and exhibit quasi-periodic behavior on top of broader subpulse emission, with periods of the order of a few μ s. By measuring their widths and periodicities from single pulse intensity profiles and their autocorrelation functions, we extend the microstructure timescale–rotation period relationship by more than an order of magnitude down to rotation periods ∼5 ms, and find it to be consistent with the relationship derived earlier for normal pulsars. The similarity of behavior is remarkable, given the significantly different physical properties of MSPs and normal period pulsars, and rules out several previous speculations about the possible different characteristics of microstructure in MSP radio emission. We discuss the possible reasons for the non-detection of these features in previous high time resolution MSP studies along with the physical implications of our results, both in terms of a geometric beam sweeping model and temporal modulation model for micropulse production.

An adaptive filtering method based on EMD for X-ray pulsar navigation with uncertain measurement noise

Directory of Open Access Journals (Sweden)

Li N.

2017-01-01

Full Text Available Affected by the unstable pulse radiation and the pulsar directional errors, the statistical characteristics of the pulsar measurement noise may vary with time slowly and cannot be accurately determined, which cause the filtering accuracy of the extended Kalman filter(EKF in pulsar navigation positioning system decline sharply or even diverge. To solve this problem, an adaptive extended Kalman filtering algorithm based on the empirical mode decomposition(EMD is proposed. In this method, the high frequency noise is separated from measurement information of pulsar by the method of EMD, and the noise variance can be estimated to update the parameters of EKF. The simulation results demonstrate that compared with conventional EKF, the proposed method can adaptively track the change of the measurement noise, and still keeps high estimation accuracy with unknown measurement noise, the positioning accuracy of the pulsar navigation is improved simultaneously.

Binary and Millisecond Pulsars.

Science.gov (United States)

Lorimer, Duncan R

2008-01-01

We review the main properties, demographics and applications of binary and millisecond radio pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1800. There are now 83 binary and millisecond pulsars associated with the disk of our Galaxy, and a further 140 pulsars in 26 of the Galactic globular clusters. Recent highlights include the discovery of the young relativistic binary system PSR J1906+0746, a rejuvination in globular cluster pulsar research including growing numbers of pulsars with masses in excess of 1.5 M ⊙ , a precise measurement of relativistic spin precession in the double pulsar system and a Galactic millisecond pulsar in an eccentric ( e = 0.44) orbit around an unevolved companion. Supplementary material is available for this article at 10.12942/lrr-2008-8.

THE EINSTEIN-HOME SEARCH FOR RADIO PULSARS AND PSR J2007+2722 DISCOVERY

Energy Technology Data Exchange (ETDEWEB)

Allen, B.; Knispel, B.; Aulbert, C.; Bock, O.; Eggenstein, H. B.; Fehrmann, H.; Machenschalk, B. [Max-Planck-Institut fuer Gravitationsphysik, D-30167 Hannover (Germany); Cordes, J. M.; Brazier, A.; Chatterjee, S. [Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States); Deneva, J. S. [Arecibo Observatory, HC3 Box 53995, Arecibo, PR 00612 (United States); Hessels, J. W. T. [ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo (Netherlands); Anderson, D. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Demorest, P. B. [NRAO (National Radio Astronomy Observatory), Charlottesville, VA 22903 (United States); Gotthelf, E. V. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Hammer, D. [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI 53211 (United States); Kaspi, V. M. [Department of Physics, McGill University, Montreal, QC H3A2T8 (Canada); Kramer, M. [Max-Planck-Institut fuer Radioastronomie, D-53121 Bonn (Germany); Lyne, A. G. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL (United Kingdom); McLaughlin, M. A., E-mail: bruce.allen@aei.mpg.de [Department of Physics, West Virginia University, Morgantown, WV 26506 (United States); and others

2013-08-20

Einstein-Home aggregates the computer power of hundreds of thousands of volunteers from 193 countries, to search for new neutron stars using data from electromagnetic and gravitational-wave detectors. This paper presents a detailed description of the search for new radio pulsars using Pulsar ALFA survey data from the Arecibo Observatory. The enormous computing power allows this search to cover a new region of parameter space; it can detect pulsars in binary systems with orbital periods as short as 11 minutes. We also describe the first Einstein-Home discovery, the 40.8 Hz isolated pulsar PSR J2007+2722, and provide a full timing model. PSR J2007+2722's pulse profile is remarkably wide with emission over almost the entire spin period. This neutron star is most likely a disrupted recycled pulsar, about as old as its characteristic spin-down age of 404 Myr. However, there is a small chance that it was born recently, with a low magnetic field. If so, upper limits on the X-ray flux suggest but cannot prove that PSR J2007+2722 is at least {approx}100 kyr old. In the future, we expect that the massive computing power provided by volunteers should enable many additional radio pulsar discoveries.

Understanding the spectral and timing behaviour of a newly discovered transient X-ray pulsar Swift J0243.6+6124

DEFF Research Database (Denmark)

Jaisawal, Gaurava K.; Naik, Sachindra; Chenevez, Jérôme

2018-01-01

We present the results obtained from timing and spectral studies of the newly discovered accreting X-ray binary pulsar Swift J0243.6+6124 using Nuclear Spectroscopy Telescope Array observation in 2017 October at a flux level of ~280 mCrab. Pulsations at 9.854 23(5) s were detected in the X......-ray light curves of the pulsar. Pulse profiles of the pulsar were found to be strongly energy dependent. A broad profile at lower energies was found to evolve into a double-peaked profile in ≥ 30 keV. The 3-79 keV continuum spectrum of the pulsar was well described with a negative and positive exponential...

Public acceptance of fusion energy and scientific feasibility of a fusion reactor. Design of inductively driven long pulse tokamak reactors: IDLT

International Nuclear Information System (INIS)

Ogawa, Yuichi

1998-01-01

Based on scientific data based adopted for designing ITER plasmas and on the advancement of fusion nuclear technology from the recent R and D program, the scientific feasibility of inductively-driven tokamak fusion reactors is studied. A low wall-loading DEMO fusion reactor is designed, which utilizes an austenitic stainless steel in conjunction with significant data bases and operating experiences, since we have given high priority to the early and reliable realization of a tokamak fusion plasma over the cost performance. Since the DEMO reactor with the relatively large volume (i.e., major radius of 10 m) is employed, plasma ignition is achievable with a low fusion power of 0.8 GW, and an operation period of 4 - 5 hours is available only with inductive current drive. Disadvantages of pulsed operation in commercial fusion reactors include fatigue in structural materials and the necessity of an energy storage system to compensate the electric power during the dwell time. To overcome these disadvantages, a pulse length is prolonged up to about 10 hours, resulting in the remarkable reduction of the total cycle number to 10 4 during the life of the fusion plant. (author)

Transient temperature response of in-vessel components due to pulsed operation in tokamak fusion experimental reactor (FER)

International Nuclear Information System (INIS)

Minato, Akio; Tone, Tatsuzo

1985-12-01

A transient temperature response of the in-vessel components (first wall, blanket, divertor/limiter and shielding) surrounding plasma in Tokamak Fusion Experimental Reactor (FER) has been analysed. Transient heat load during start up/shut down and pulsed operation cycles causes the transient temperature response in those components. The fatigue lifetime of those components significantly depends upon the resulting cyclic thermal stress. The burn time affects the temperature control in the solid breeder (Li 2 O) and also affects the thermo-mechanical design of the blanket and shielding which are constructed with thick structure. In this report, results of the transient temperature response obtained by the heat transfer and conduction analyses for various pulsed operation scenarios (start up, shut down, burn and dwell times) have been investigated in view of thermo-mechanical design of the in-vessel components. (author)

The largest glitch observed in the Crab pulsar

Science.gov (United States)

Shaw, B.; Lyne, A. G.; Stappers, B. W.; Weltevrede, P.; Bassa, C. G.; Lien, A. Y.; Mickaliger, M. B.; Breton, R. P.; Jordan, C. A.; Keith, M. J.; Krimm, H. A.

2018-05-01

We have observed a large glitch in the Crab pulsar (PSR B0531+21). The glitch occurred around MJD 58064 (2017 November 8) when the pulsar underwent an increase in the rotation rate of Δν = 1.530 × 10-5 Hz, corresponding to a fractional increase of Δν/ν = 0.516 × 10-6 making this event the largest glitch ever observed in this source. Due to our high-cadence and long-dwell time observations of the Crab pulsar we are able to partially resolve a fraction of the total spin-up of the star. This delayed spin-up occurred over a timescale of ˜1.7 days and is similar to the behaviour seen in the 1989 and 1996 large Crab pulsar glitches. The spin-down rate also increased at the glitch epoch by Δ \\dot{ν } / \\dot{ν } = 7 × 10^{-3}. In addition to being the largest such event observed in the Crab, the glitch occurred after the longest period of glitch inactivity since at least 1984 and we discuss a possible relationship between glitch size and waiting time. No changes to the shape of the pulse profile were observed near the glitch epoch at 610 MHz or 1520 MHz, nor did we identify any changes in the X-ray flux from the pulsar. The long-term recovery from the glitch continues to progress as \\dot{ν } slowly rises towards pre-glitch values. In line with other large Crab glitches, we expect there to be a persistent change to \\dot{ν }. We continue to monitor the long-term recovery with frequent, high quality observations.

THE PULSAR SEARCH COLLABORATORY: DISCOVERY AND TIMING OF FIVE NEW PULSARS

Energy Technology Data Exchange (ETDEWEB)

Rosen, R.; Swiggum, J.; McLaughlin, M. A.; Lorimer, D. R.; Yun, M.; Boyles, J. [West Virginia University, White Hall, Morgantown, WV 26506 (United States); Heatherly, S. A.; Scoles, S. [NRAO, P.O. Box 2, Green Bank, WV 24944 (United States); Lynch, R. [McGill University, Rutherford Physics Building, 3600 Rue University, Montreal, QC H3A 2T8 (Canada); Kondratiev, V. I. [ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo (Netherlands); Ransom, S. M. [NRAO, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Moniot, M. L.; Thompson, C. [James River High School, 9906 Springwood Road, Buchanan, VA 24066 (United States); Cottrill, A.; Raycraft, M. [Lincoln High School, 100 Jerry Toth Drive, Shinnston, WV 26431 (United States); Weaver, M. [Broadway High School, 269 Gobbler Drive, Broadway, VA 22815 (United States); Snider, A. [Sherando High School, 185 South Warrior Drive, Stephens City, VA 22655 (United States); Dudenhoefer, J.; Allphin, L. [Hedgesville High School, 109 Ridge Road North, Hedgesville, WV 25427 (United States); Thorley, J., E-mail: Rachel.Rosen@mail.wvu.edu [Strasburg High School, 250 Ram Drive, Strasburg, VA 22657 (United States); and others

2013-05-01

We present the discovery and timing solutions of five new pulsars by students involved in the Pulsar Search Collaboratory, a NSF-funded joint program between the National Radio Astronomy Observatory and West Virginia University designed to excite and engage high-school students in Science, Technology, Engineering, and Mathematics (STEM) and related fields. We encourage students to pursue STEM fields by apprenticing them within a professional scientific community doing cutting edge research, specifically by teaching them to search for pulsars. The students are analyzing 300 hr of drift-scan survey data taken with the Green Bank Telescope at 350 MHz. These data cover 2876 deg{sup 2} of the sky. Over the course of five years, more than 700 students have inspected diagnostic plots through a web-based graphical interface designed for this project. The five pulsars discovered in the data have spin periods ranging from 3.1 ms to 4.8 s. Among the new discoveries are PSR J1926-1314, a long period, nulling pulsar; PSR J1821+0155, an isolated, partially recycled 33 ms pulsar; and PSR J1400-1438, a millisecond pulsar in a 9.5 day orbit whose companion is likely a white dwarf star.

On the passage of radiation through inhomogeneous, moving media. XI - Nonlinear effects on ray paths in the geometrical optics approximation. [in pulsar magnetospheres

Science.gov (United States)

Lee, M. A.; Lerche, I.

1974-01-01

Study illustrating how the presence of a high-intensity pulse of radiation can distort its own passage through a plane differentially shearing medium. It is demonstrated that the distortion is a sensitive function of the precise, and detailed, variation of the medium's refractive index by considering a couple of simple examples which are worked out numerically. In view of the high-intensity pulses observed from pulsars (approximately 10 to the 30th ergs per pulse), it is believed that the present calculations are of more than academic interest in helping unravel the fundamental properties of pulse production in, and propagating through, differentially sheared media - such as pulsars' magnetospheres within the so-called speed-of-light circle.

Galactic population of pulsars

International Nuclear Information System (INIS)

Lyne, A.G.; Manchester, R.N.

1985-01-01

In order to draw statistical conclusions about the overall population of pulsars in the Galaxy, a sample of 316 pulsars detected in surveys carried out at Jodrell Bank, Arecibo, Molonglo, and Green Bank has been analysed. The important selection effects of each survey are quantified and a statistically reliable pulsar distance scale based on a model for the large-scale distribution of free electrons in the Galaxy is described. These results allow the spatial and luminosity distribution functions of galactic pulsars to be computed. It is concluded that the Galaxy contains approximately 70 000 potentially observable pulsars with luminosities above 0.3 mJy kpc 2 . The period and luminosity evolution of pulsars, is also considered. (author)

The Green Bank North Celestial Cap Pulsar Survey: New Pulsars and Future Prospects

Science.gov (United States)

Lynch, Ryan S.; Swiggum, Joe; Stovall, Kevin; Chawla, Pragya; DeCesar, Megan E.; Fonseca, Emmanuel; Levin, Lina; Cui, Bingyi; Kondratiev, Vlad; Archibald, Anne; Boyles, Jason; Hessels, Jason W. T.; Jenet, Fredrick; Kaplan, David; Karako-Argaman, Chen; Kaspi, Victoria; Martinez, Jose; McLaughlin, Maura; Ransom, Scott M.; Roberts, Mallory; Siemens, Xavier; Spiewak, Renee; Stairs, Ingrid; van Leeuwn, Joeri; Green Bank North Celestial Cap Survey Collaboration

2018-01-01

The Green Bank North Celestial Cap pulsar survey is the most successful low frequency pulsar survey ever. GBNCC uses the Green Bank telescope to cover the full visible sky at 350 MHz. With the survey over 70% complete, we have discovered over 150 pulsars, including 20 MSPs and 11 RRATs. I will report on the current status of the survey and plans for its completion in the coming years. I will also report on several discoveries including: timing solutions for dozens of new pulsars; new high precision MSPs and their suitability for inclusion in pulsar timing arrays; a new relativistic double neutron star system; new pulsar mass measurements; proper motion measurements for several MSPs; a new mode changing pulsar; interesting new MSP binaries; nulling fraction analyses; and possible implications of the lack of any fast radio bursts in the survey so far.

Search for VHE γ-ray emission from the direction of the two millisecond pulsars PSR J0437-4715 and PSR J1824-2452 and the composite supernova remnant Kes 75 with H.E.S.S

International Nuclear Information System (INIS)

Fuessling, Matthias

2012-01-01

This work reports on the search for pulsed and steady very-high energy (VHE) gamma-ray emission in the energy range extending from 100 GeV up to 100 TeV from the direction of three pulsars with the High Energy Stereoscopic System (H.E.S.S.). Pulsed gamma-ray radiation from pulsars with energies beyond 100 GeV was found thus far only for the young and energetic Crab pulsar. A special class of pulsar wind nebulae (PWNe) is associated with composite supernova remnants (SNRs) where the PWN is centered in an expanding SNR shell. In the first part of this thesis, the results on the search for pulsed and steady VHE gamma-ray emission from the two millisecond pulsars, PSR J0437-4715 and PSR J1824-2452, are presented. Parts of the observations were conducted in a special trigger setup (the topological trigger with convergent pointing) to reduce the energy threshold of the instrument. No signal of pulsed or steady emission is found and upper limits on the pulsed and steady gamma-ray flux are derived. The upper limits on the pulsed gamma-ray flux are compared to existing model predictions and, in the case of PSR J1824-2452, allow the range of possible viewing geometries in some models to be constrained. In the second part of this work, results on the search for pulsed and steady VHE gamma-ray emission from the direction of the composite SNR Kes 75 are presented. The PWN in the center of Kes 75 is powered by a very young and powerful pulsar, PSR J1846-0258, that has an exceptionally high magnetic field. While no hint for pulsed emission is found, steady VHE gamma-ray emission is detected with a statistical significance of 10 sigma from a point-like source. The VHE gamma-ray emission is spatially coincident with the PWN and the SNR shell. Both are discussed as a possible origin for the observed emission. The pulsar of Kes 75 would be the youngest pulsar known to date to power a VHE PWN.

PSR J1618-3921: a recycled pulsar in an eccentric orbit

Science.gov (United States)

Octau, F.; Cognard, I.; Guillemot, L.; Tauris, T. M.; Freire, P. C. C.; Desvignes, G.; Theureau, G.

2018-04-01

Context. The 11.99 ms pulsar PSR J1618-3921 orbits a He white dwarf companion of probably low mass with a period of 22.7 d. The pulsar was discovered in a survey of the intermediate Galactic latitudes at 1400 MHz that was conducted with the Parkes radio telescope in the late 1990s. Although PSR J1618-3921 was discovered more than 15 years ago, only limited information has been published about this pulsar, which has a surprisingly high orbital eccentricity (e ≃ 0.027) considering its high spin frequency and the likely low mass of the companion. Aims: The focus of this work is a precise measurement of the spin and the astrometric and orbital characteristics of PSR J1618-3921. This was done with timing observations made at the Nançay Radio Telescope from 2009 to 2017. Methods: We analyzed the timing data recorded at the Nançay Radio Telescope over several years to characterize the properties of PSR J1618-3921. A rotation ephemeris for this pulsar was obtained by analyzing the arrival times of the radio pulses at the telescope. Results: We confirm the unusual eccentricity of PSR J1618-3921 and discuss several hypotheses regarding its formation in the context of other discoveries of recycled pulsars in eccentric orbits.

Supernova 1987A Interpreted through the SLIP Pulsar Model

Science.gov (United States)

Middleditch, John

2010-01-01

The model of pulsar emission through superluminally induced polarization currents (SLIP) predicts that pulsations produced by such currents, induced by a rotating, magnetized body at many light cylinder radii, as would be the case for a neutron star born within any star of >1.5 solar masses, will drive pulsations close to the axis of rotation. Such highly collimated pulsations (), and later, in less collimated form, the bipolarity of SN 1987A itself. The pulsations and jet interacted with circumstellar material (CM), to produce features observed in the very early light curve which correspond to: 1) the entry of the pulsed beam into the CM; 2) the entry of the 0.95 c particles into the CM; 3) the exit of the pulsed beam from the CM (with contributions in the B and I bands -- the same as later inferred/observed for its 2.14 ms pulsations); and 4) the exit of the fastest particles from the CM. Because of the energy requirements of the jet in these early stages, the spindown required of its pulsar could exceed 1e-5 Hz/s at a rotation rate of 500 Hz. There is no reason to suggest that this mechanism is not universally applicable to all SNe with gaseous remnants remaining, and thus SN 1987A is the Rosetta Stone for 99% of SNe, gamma-ray bursts, and millisecond pulsars. This work was supported in part by the Department of Energy through the Los Alamos Directed Research Grant DR20080085.

A compact nanosecond pulse generator for DBD tube characterization

Science.gov (United States)

Rai, S. K.; Dhakar, A. K.; Pal, U. N.

2018-03-01

High voltage pulses of very short duration and fast rise time are required for generating uniform and diffuse plasma under various operating conditions. Dielectric Barrier Discharge (DBD) has been generated by high voltage pulses of short duration and fast rise time to produce diffuse plasma in the discharge gap. The high voltage pulse power generators have been chosen according to the requirement for the DBD applications. In this paper, a compact solid-state unipolar pulse generator has been constructed for characterization of DBD plasma. This pulsar is designed to provide repetitive pulses of 315 ns pulse width, pulse amplitude up to 5 kV, and frequency variation up to 10 kHz. The amplitude of the output pulse depends on the dc input voltage. The output frequency has been varied by changing the trigger pulse frequency. The pulsar is capable of generating pulses of positive or negative polarity by changing the polarity of pulse transformer's secondary. Uniform and stable homogeneous dielectric barrier discharge plasma has been produced successfully in a xenon DBD tube at 400-mbar pressure using the developed high voltage pulse generator.

Neutral beam in ALVAND IIC tokamak

International Nuclear Information System (INIS)

Ghrannevisse, M.; Moradshahi, M.; Avakian, M.

1992-01-01

Neutral beams have a wide application in tokamak experiments. It used to heat; fuel; adjust electric potentials in plasmas and diagnose particles densities and momentum distributions. It may be used to sustain currents in tokamaks to extend the pulse length. A 5 KV; 500 mA ion source has been constructed by plasma physics group, AEOI and it used to produce plasma and study the plasma parameters. Recently this ion source has been neutralized and it adapted to a neutral beam source; and it used to heat a cylindrical DC plasma and the plasma of ALVAND IIC Tokamak which is a small research tokamak with a minor radius of 12.6 cm, and a major radius of 45.5 cm. In this paper we report the neutralization of the ion beam and the results obtained by injection of this neutral beam into plasmas. (author) 2 refs., 4 figs

Constraining Gamma-Ray Pulsar Gap Models with a Simulated Pulsar Population

Science.gov (United States)

Pierbattista, Marco; Grenier, I. A.; Harding, A. K.; Gonthier, P. L.

2012-01-01

With the large sample of young gamma-ray pulsars discovered by the Fermi Large Area Telescope (LAT), population synthesis has become a powerful tool for comparing their collective properties with model predictions. We synthesised a pulsar population based on a radio emission model and four gamma-ray gap models (Polar Cap, Slot Gap, Outer Gap, and One Pole Caustic). Applying gamma-ray and radio visibility criteria, we normalise the simulation to the number of detected radio pulsars by a select group of ten radio surveys. The luminosity and the wide beams from the outer gaps can easily account for the number of Fermi detections in 2 years of observations. The wide slot-gap beam requires an increase by a factor of 10 of the predicted luminosity to produce a reasonable number of gamma-ray pulsars. Such large increases in the luminosity may be accommodated by implementing offset polar caps. The narrow polar-cap beams contribute at most only a handful of LAT pulsars. Using standard distributions in birth location and pulsar spin-down power (E), we skew the initial magnetic field and period distributions in a an attempt to account for the high E Fermi pulsars. While we compromise the agreement between simulated and detected distributions of radio pulsars, the simulations fail to reproduce the LAT findings: all models under-predict the number of LAT pulsars with high E , and they cannot explain the high probability of detecting both the radio and gamma-ray beams at high E. The beaming factor remains close to 1.0 over 4 decades in E evolution for the slot gap whereas it significantly decreases with increasing age for the outer gaps. The evolution of the enhanced slot-gap luminosity with E is compatible with the large dispersion of gamma-ray luminosity seen in the LAT data. The stronger evolution predicted for the outer gap, which is linked to the polar cap heating by the return current, is apparently not supported by the LAT data. The LAT sample of gamma-ray pulsars

THE PULSAR SEARCH COLLABORATORY: DISCOVERY AND TIMING OF FIVE NEW PULSARS

International Nuclear Information System (INIS)

Rosen, R.; Swiggum, J.; McLaughlin, M. A.; Lorimer, D. R.; Yun, M.; Boyles, J.; Heatherly, S. A.; Scoles, S.; Lynch, R.; Kondratiev, V. I.; Ransom, S. M.; Moniot, M. L.; Thompson, C.; Cottrill, A.; Raycraft, M.; Weaver, M.; Snider, A.; Dudenhoefer, J.; Allphin, L.; Thorley, J.

2013-01-01

We present the discovery and timing solutions of five new pulsars by students involved in the Pulsar Search Collaboratory, a NSF-funded joint program between the National Radio Astronomy Observatory and West Virginia University designed to excite and engage high-school students in Science, Technology, Engineering, and Mathematics (STEM) and related fields. We encourage students to pursue STEM fields by apprenticing them within a professional scientific community doing cutting edge research, specifically by teaching them to search for pulsars. The students are analyzing 300 hr of drift-scan survey data taken with the Green Bank Telescope at 350 MHz. These data cover 2876 deg 2 of the sky. Over the course of five years, more than 700 students have inspected diagnostic plots through a web-based graphical interface designed for this project. The five pulsars discovered in the data have spin periods ranging from 3.1 ms to 4.8 s. Among the new discoveries are PSR J1926–1314, a long period, nulling pulsar; PSR J1821+0155, an isolated, partially recycled 33 ms pulsar; and PSR J1400–1438, a millisecond pulsar in a 9.5 day orbit whose companion is likely a white dwarf star.

EINSTEIN-HOME DISCOVERY OF 24 PULSARS IN THE PARKES MULTI-BEAM PULSAR SURVEY

Energy Technology Data Exchange (ETDEWEB)

Knispel, B.; Kim, H.; Allen, B.; Aulbert, C.; Bock, O.; Eggenstein, H.-B.; Fehrmann, H.; Machenschalk, B. [Albert-Einstein-Institut, Max-Planck-Institut fuer Gravitationsphysik, D-30167 Hannover (Germany); Eatough, R. P.; Keane, E. F.; Kramer, M. [Max-Planck-Institut fuer Radioastronomie, D-53121 Bonn (Germany); Anderson, D. [University of California at Berkeley, Berkeley, CA 94720 (United States); Crawford, F.; Rastawicki, D. [Department of Physics and Astronomy, Franklin and Marshall College, P.O. Box 3003, Lancaster, PA 17604 (United States); Hammer, D.; Papa, M. A.; Siemens, X. [Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211 (United States); Lyne, A. G. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); Miller, R. B. [Department of Physics, West Virginia University, 111 White Hall, Morgantown, WV 26506 (United States); Sarkissian, J., E-mail: benjamin.knispel@aei.mpg.de [CSIRO Parkes Observatory, Parkes, NSW 2870 (Australia); and others

2013-09-10

We have conducted a new search for radio pulsars in compact binary systems in the Parkes multi-beam pulsar survey (PMPS) data, employing novel methods to remove the Doppler modulation from binary motion. This has yielded unparalleled sensitivity to pulsars in compact binaries. The required computation time of Almost-Equal-To 17, 000 CPU core years was provided by the distributed volunteer computing project Einstein-Home, which has a sustained computing power of about 1 PFlop s{sup -1}. We discovered 24 new pulsars in our search, 18 of which were isolated pulsars, and 6 were members of binary systems. Despite the wide filterbank channels and relatively slow sampling time of the PMPS data, we found pulsars with very large ratios of dispersion measure (DM) to spin period. Among those is PSR J1748-3009, the millisecond pulsar with the highest known DM ( Almost-Equal-To 420 pc cm{sup -3}). We also discovered PSR J1840-0643, which is in a binary system with an orbital period of 937 days, the fourth largest known. The new pulsar J1750-2536 likely belongs to the rare class of intermediate-mass binary pulsars. Three of the isolated pulsars show long-term nulling or intermittency in their emission, further increasing this growing family. Our discoveries demonstrate the value of distributed volunteer computing for data-driven astronomy and the importance of applying new analysis methods to extensively searched data.

Tokamak burn cycle study: a data base for comparing long pulse and steady-state power reactors

International Nuclear Information System (INIS)

Ehst, D.A.; Brooks, J.N.; Cha, Y.; Evans, K. Jr.; Hassanein, A.; Kim, S.; Majumdar, S.; Misra, B.; Stevens, H.C.

1983-11-01

Several distinct operating modes (conventional ohmic, noninductive steady state, internal transformer, etc.) have been proposed for tokamaks. Our study focuses on capital costs and lifetime limitations of reactor subsystems in an attempt to quantify sensitivity to pulsed operation. Major problem areas considered include: thermal fatigue on first wall, limiter/divertor; thermal energy storage; fatigue and eddy current heating in toroidal field coils; electric power supply costs; and noninductive driver costs. We assume a high availability and low cost of energy will be mandatory for a commercial fusion reactor, and we characterize improvements in physics (current drive efficiency) and engineering (superior materials) which will help achieve these goals for different burn cycles

Increasing Pulsar Timing Array Sensitivity Through Addition of Millisecond Pulsars

Science.gov (United States)

DeCesar, Megan E.; Crawford, Fronefield; Ferrara, Elizabeth; Lynch, Ryan; Mingarelli, Chiara; Levin Preston, Lina; Ransom, Scott; Romano, Joseph; Simon, Joseph; Spiewak, Renee; Stovall, Kevin; Swiggum, Joe; Taylor, Stephen; Green Bank North Celestial Cap Pulsar Survey, Fermi LAT Collaboration, Fermi Pulsar Search Consortium

2018-01-01

Siemens et al. (2013) and Taylor et al. (2016) demonstrated the importance of increasing the number of millisecond pulsars (MSPs) in pulsar timing arrays (PTAs) in order to increase the sensitivity of the array and decrease the time-to-detection of a gravitational wave background (GWB). In particular, they predict that adding four MSPs per year to the NANOGrav and International PTAs will likely yield a GWB detection in less than a decade. A more even distribution of MSPs across the sky is also important for discriminating a GWB signal from a non-quadrupolar background (Sampson et al., in prep). Pulsar surveys and targeted searches have consistently led to additions of 4 or more MSPs per year to PTAs. I will describe these ongoing efforts, particularly in the context of the Green Bank North Celestial Cap pulsar survey and Fermi-guided searches at Green Bank and Arecibo that seek to find MSPs in low-pulsar-density regions of the sky.

TIBER (Tokamak Ignition/Burn Experimental Reactor) II as a precursor to an international thermonuclear experimental reactor

International Nuclear Information System (INIS)

Henning, C.D.; Gilleland, J.R.

1988-01-01

The Tokamak Ignition/Burn Experimental Reactor (TIBER) was pursued in the US as one option for an International Thermonuclear Experimental Reactor (ITER). This concept evolved from earlier work on the Tokamak Fusion Core Experiment (TFCX) to develop a small, ignited tokamak. While the copper-coil versions of TFCX became the short-pulsed, 1.23-m radius, Compact Ignition Tokamak (CIT), the superconducting TIBER with long pulse or steady state and a 2.6-m radius was considered for international collaboration. Recently the design was updated to TIBER II, to accommodate more conservative confinement scaling, double-poloidal divertors for impurity control, steady-state current drive, and nuclear testing. 18 refs., 1 fig

Pulsar timing and its applications

OpenAIRE

Manchester, R N

2018-01-01

Pulsars are remarkably precise "celestial clocks" that can be used to explore many different aspects of physics and astrophysics. In this article I give a brief summary of pulsar properties and describe some of the applications of pulsar timing, including tests of theories of gravitation, efforts to detect low-frequency gravitational waves using pulsar timing arrays and establishment a "pulsar timescale".

Pulsar slow-down epochs

International Nuclear Information System (INIS)

Heintzmann, H.; Novello, M.

1981-01-01

The relative importance of magnetospheric currents and low frequency waves for pulsar braking is assessed and a model is developed which tries to account for the available pulsar timing data under the unifying aspect that all pulsars have equal masses and magnetic moments and are born as rapid rotators. Four epochs of slow-down are distinguished which are dominated by different braking mechanisms. According to the model no direct relationship exists between 'slow-down age' and true age of a pulsar and leads to a pulsar birth-rate of one event per hundred years. (Author) [pt

Binary and Millisecond Pulsars

Directory of Open Access Journals (Sweden)

Lorimer Duncan R.

2005-11-01

Full Text Available We review the main properties, demographics and applications of binary and millisecond radio pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1700. There are now 80 binary and millisecond pulsars associated with the disk of our Galaxy, and a further 103 pulsars in 24 of the Galactic globular clusters. Recent highlights have been the discovery of the first ever double pulsar system and a recent flurry of discoveries in globular clusters, in particular Terzan 5.

Technology and plasma-materials interaction processes of tokamak disruptions

International Nuclear Information System (INIS)

McGrath, R.T.; Kellman, A.G.

1992-01-01

A workshop on the technology and plasma-materials interaction processes of tokamak disruptions was held April 3, 1992 in Monterey, California, as a satellite meeting of the 10th International Conference on Plasma-Surface Interactions. The objective was to bring together researchers working on disruption measurements in operating tokamaks, those performing disruption simulation experiments using pulsed plasma gun, electron beam and laser systems, and computational physicists attempting to model the evolution and plasma-materials interaction processes of tokamak disruptions. This is a brief report on the workshop. 4 refs

Oldest pulsars in the Universe

International Nuclear Information System (INIS)

Shaham, J.

1987-01-01

Since the discovery of the Vulpecula pulsar two more superfast pulsars have been reported. In 1983 a 6.13-millisecond pulsar (called 1953 + 29) was announced, and in 1986 a 5.362-millisecond pulsar (called 1855 + 09) was publicized. A candidate for a fourth has been mentioned. As more evidence becomes available, it seems increasingly likely that the superfast pulsars can be explained only as a part of a new class of pulsars. Although many of the details of the class remain obscured, some general facts are emerging. Perhaps most interesting of all is the great age these new celestial objects are thought to have. Ordinary pulsars are relatively young, typically less than a million years old; the Crab pulsar, which is the youngest one known, is a mere infant of 932 years. The superfast pulsars, in comparison, are thought to be ancient. They are probably the result of evolutionary processes that could go back as much as a billion years, or one-twentieth of the age of the universe, and they are likely to live for several billion years more. 8 figures

Millisecond Pulsar Timing Precision with NICER

Science.gov (United States)

Deneva, Julia; Ray, Paul S.; Ransom, Scott; Wood, Kent S.; Kerr, Matthew T.; Lommen, Andrea; Arzoumanian, Zaven; Black, Kevin; Gendreau, Keith C.; Lewandowska, Natalia; Markwardt, Craig B.; Price, Samuel; Winternitz, Luke

2018-01-01

The Neutron Star Interior Composition Explorer (NICER) is an array of 56 X-ray detectors mounted on the outside of the International Space Station. It allows high-precision timing of millisecond pulsars (MSPs) without the pulse broadening effects due to dispersion and scattering by the interstellar medium that plague radio timing. We present initial timing results from four months of NICER data on the MSPs B1937+21, B1821-24, and J0218+4232, and compare them to simulations and theoretical models for X-ray times-of-arrival, and radio observations.

Algorithms for searching Fast radio bursts and pulsars in tight binary systems.

Science.gov (United States)

Zackay, Barak

2017-01-01

Fast radio bursts (FRB's) are an exciting, recently discovered, astrophysical transients which their origins are unknown.Currently, these bursts are believed to be coming from cosmological distances, allowing us to probe the electron content on cosmological length scales. Even though their precise localization is crucial for the determination of their origin, radio interferometers were not extensively employed in searching for them due to computational limitations.I will briefly present the Fast Dispersion Measure Transform (FDMT) algorithm,that allows to reduce the operation count in blind incoherent dedispersion by 2-3 orders of magnitude.In addition, FDMT enables to probe the unexplored domain of sub-microsecond astrophysical pulses.Pulsars in tight binary systems are among the most important astrophysical objects as they provide us our best tests of general relativity in the strong field regime.I will provide a preview to a novel algorithm that enables the detection of pulsars in short binary systems using observation times longer than an orbital period.Current pulsar search programs limit their searches for integration times shorter than a few percents of the orbital period.Until now, searching for pulsars in binary systems using observation times longer than an orbital period was considered impossible as one has to blindly enumerate all options for the Keplerian parameters, the pulsar rotation period, and the unknown DM.Using the current state of the art pulsar search techniques and all computers on the earth, such an enumeration would take longer than a Hubble time. I will demonstrate that using the new algorithm, it is possible to conduct such an enumeration on a laptop using real data of the double pulsar PSR J0737-3039.Among the other applications of this algorithm are:1) Searching for all pulsars on all sky positions in gamma ray observations of the Fermi LAT satellite.2) Blind searching for continuous gravitational wave sources emitted by pulsars with

Dynamic stabilization of disruption precursors in tokamak

Energy Technology Data Exchange (ETDEWEB)

Maoquan, Wang; Jianshan, Mao; Yuan, Pan [Academia Sinica, Hefei, AH (China). Inst. of Plasma Physics

1994-12-01

A method for dynamic stabilization of the disruption precursors in tokamak is proposed, that is a controlled ac current induced and added to the equilibrium current. The ac currents applied can be a sine alternative current with a relevant frequency, or a pulsed current with a suitable pulsed width {tau} and or a discontinuous pulsed current whose width {tau} is very shorter than the intervals between pulses, and or a `sawtooth` pulsed current with the time of ramp phase of the sawtooth is very much shorter than the sawtooth descending time, the ratio of them can be {<=}10{sup -3}. The physical model of the ac current drive is analyzed in detail. The suppression role of the ac current on the MHD perturbations was analyzed in theory and proved numerically. It is indicated that the ac current can make the discontinuous derivative, {Delta}`, more favorable for the tearing mode stabilities, and so, as long as the parameters of the applied ac currents are selected suitably, the MHD perturbations can be suppressed effectively, the perturbations will be in the zero-growing state, the profile of the plasma current and temperature remain in the initial states and not variate basically, the tokamak be in the stabilized operation state. (8 figs.).

Tokamak reactor startup power

International Nuclear Information System (INIS)

Weldon, D.M.; Murray, J.G.

1983-01-01

Tokamak startup with ohmic heating (OH)-induced voltages requires rather large voltages and power supplies. On present machines, with no radiofrequency (rf)-assist provisions, hundreds of volts have been specified for their designs. With the addition of electron cyclotron resonant heating (ECRH) assist, the design requirements have been lowered. To obtain information on the cost and complexity associated with this ECRH-assisted, OH-pulsed startup voltage for ignition-type machines, a trade-off study was completed. The Fusion Engineering Device (FED) configuration was selected as a model because information was available on the structure. The data obtained are applicable to all tokamaks of this general size and complexity, such as the Engineering Test Reactor

Detection of long nulls in PSR B1706-16, a pulsar with large timing irregularities

Science.gov (United States)

Naidu, Arun; Joshi, Bhal Chandra; Manoharan, P. K.; Krishnakumar, M. A.

2018-04-01

Single pulse observations, characterizing in detail, the nulling behaviour of PSR B1706-16 are being reported for the first time in this paper. Our regular long duration monitoring of this pulsar reveals long nulls of 2-5 h with an overall nulling fraction of 31 ± 2 per cent. The pulsar shows two distinct phases of emission. It is usually in an active phase, characterized by pulsations interspersed with shorter nulls, with a nulling fraction of about 15 per cent, but it also rarely switches to an inactive phase, consisting of long nulls. The nulls in this pulsar are concurrent between 326.5 and 610 MHz. Profile mode changes accompanied by changes in fluctuation properties are seen in this pulsar, which switches from mode A before a null to mode B after the null. The distribution of null durations in this pulsar is bimodal. With its occasional long nulls, PSR B1706-16 joins the small group of intermediate nullers, which lie between the classical nullers and the intermittent pulsars. Similar to other intermediate nullers, PSR B1706-16 shows high timing noise, which could be due to its rare long nulls if one assumes that the slowdown rate during such nulls is different from that during the bursts.

Pulsars for the Beginner

Science.gov (United States)

DiLavore, Phillip; Wayland, James R.

1971-01-01

Presents the history of the discovery of pulsars, observations that have been made on pulsar radiation, and theories that have been presented for its presence and origin. Illustrations using pulsar's properties are presented in mechanics, electromagnetic radiation and thermodynamics. (DS)

PULSAR.MAKING VISIBLE THE SOUND OF STARS

OpenAIRE

Lega, Ferran

2015-01-01

[EN] Pulsar, making visible the sound of stars is a comunication based on a sound Installation raised as a site-specific project to show the hidden abilities of sound to generate images and patterns on the matter, using the acoustic science of cymatics. The objective of this communication will show people how through abstract and intangible sounds from celestial orbs of cosmos (radio waves generated by electromagnetic pulses from the rotation of neutrón stars), we can create ar...

Cosmic Ray Positrons from Pulsars

Science.gov (United States)

Harding, Alice K.

2010-01-01

Pulsars are potential Galactic sources of positrons through pair cascades in their magnetospheres. There are, however, many uncertainties in establishing their contribution to the local primary positron flux. Among these are the local density of pulsars, the cascade pair multiplicities that determine the injection rate of positrons from the pulsar, the acceleration of the injected particles by the pulsar wind termination shock, their rate of escape from the pulsar wind nebula, and their propagation through the interstellar medium. I will discuss these issues in the context of what we are learning from the new Fermi pulsar detections and discoveries.

Runaway electrons during tokamak startup

International Nuclear Information System (INIS)

Sharma, A.S.; Jayakumar, R.

1988-01-01

Runaway electrons significantly affect the plasma and impurity evolution during tokamak startup. During its rise, a runaway pulse stores magnetic flux inductively; this is then released during the decay phase of the runaway pulse. This process affects plasma formation, current initiation and current buildup. Because of their relativistic velocities the runaway electrons have higher ionization and excitation rates than the plasma electrons. This leads to a significant modification of the impurity behaviour and consequently the plasma evolution. (author). 20 refs, 8 figs

Electromagnetic pulses in a strongly magnetized electron-positron plasma

International Nuclear Information System (INIS)

Yu, M.Y.; Rao, N.N.

1985-01-01

The conditions for the existence of large-amplitude localized electromagnetic wave pulses in an electron-positron plasma penetrated by a very strong ambient magnetic field are obtained. It is shown that such pulses can exist in pulsar polar magnetospheres. 12 references

Pulsar timing signal from ultralight scalar dark matter

International Nuclear Information System (INIS)

Khmelnitsky, Andrei; Rubakov, Valery

2014-01-01

An ultralight free scalar field with mass around 10 −23 −10 −22 eV is a viable dark mater candidate, which can help to resolve some of the issues of the cold dark matter on sub-galactic scales. We consider the gravitational field of the galactic halo composed out of such dark matter. The scalar field has oscillating in time pressure, which induces oscillations of gravitational potential with amplitude of the order of 10 −15 and frequency in the nanohertz range. This frequency is in the range of pulsar timing array observations. We estimate the magnitude of the pulse arrival time residuals induced by the oscillating gravitational potential. We find that for a range of dark matter masses, the scalar field dark matter signal is comparable to the stochastic gravitational wave signal and can be detected by the planned SKA pulsar timing array experiment

Observational properties of pulsars.

Science.gov (United States)

Manchester, R N

2004-04-23

Pulsars are remarkable clocklike celestial sources that are believed to be rotating neutron stars formed in supernova explosions. They are valuable tools for investigations into topics such as neutron star interiors, globular cluster dynamics, the structure of the interstellar medium, and gravitational physics. Searches at radio and x-ray wavelengths over the past 5 years have resulted in a large increase in the number of known pulsars and the discovery of new populations of pulsars, posing challenges to theories of binary and stellar evolution. Recent images at radio, optical, and x-ray wavelengths have revealed structures resulting from the interaction of pulsar winds with the surrounding interstellar medium, giving new insights into the physics of pulsars.

THE BENEFITS OF VLBI ASTROMETRY TO PULSAR TIMING ARRAY SEARCHES FOR GRAVITATIONAL RADIATION

Energy Technology Data Exchange (ETDEWEB)

Madison, D. R.; Chatterjee, S.; Cordes, J. M. [Department of Astronomy and Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14850 (United States)

2013-11-10

Precision astrometry is an integral component of successful pulsar timing campaigns. Astrometric parameters are commonly derived by fitting them as parameters of a timing model to a series of pulse times of arrival (TOAs). TOAs measured to microsecond precision over spans of several years can yield position measurements with sub-milliarcsecond precision. However, timing-based astrometry can become biased if a pulsar displays any red spin noise or a red signal produced by the stochastic gravitational wave background. We investigate how noise of different spectral types is absorbed by timing models, leading to significant estimation biases in the astrometric parameters. We find that commonly used techniques for fitting timing models in the presence of red noise (Cholesky whitening) prevent the absorption of noise into the timing model remarkably well if the time baseline of observations exceeds several years, but are inadequate for dealing with shorter pulsar data sets. Independent of timing, pulsar-optimized very long baseline interferometry (VLBI) is capable of providing position estimates precise to the sub-milliarcsecond levels needed for high-precision timing. In order to make VLBI astrometric parameters useful in pulsar timing models, the transformation between the International Celestial Reference Frame (ICRF) and the dynamical solar system ephemeris used for pulsar timing must be constrained to within a few microarcseconds. We compute a transformation between the ICRF and pulsar timing frames and quantitatively discuss how the transformation will improve in coming years. We find that incorporating VLBI astrometry into the timing models of pulsars for which only a couple of years of timing data exist will lead to more realistic assessments of red spin noise and could enhance the amplitude of gravitational wave signatures in post-fit timing residuals by factors of 20 or more.

Digital controlled pulsed electric system of the ETE tokamak. First report

International Nuclear Information System (INIS)

Barbosa, Luis Felipe de F.P.W.; Del Bosco, Edson

1997-01-01

This reports presents a summary on the thermonuclear fusion and application for energy supply purposes. The tokamak device operation and the magnetic field production systems are described. The ETE tokamak is a small aspect ratio device designed for plasma physics and thermonuclear fusion studies, which presently is under construction at the Laboratorio Associado de Plasma (LAP), Instituto Nacional de Pesquisas Espaciais (INPE) - S.J. dos Campos - S. Paulo. (author)

Burn cycle requirements comparison of pulsed and steady-state tokamak reactors

International Nuclear Information System (INIS)

Brooks, J.N.; Ehst, D.A.

1983-12-01

Burn cycle parameters and energy transfer system requirements were analyzed for an 8-m commercial tokamak reactor using four types of cycles: conventional, hybrid, internal transformer, and steady state. Not surprisingly, steady state is the best burn mode if it can be achieved. The hybrid cycle is a promising alternative to the conventional. In contrast, the internal transformer cycle does not appear attractive for the size tokamak in question

A broadband x-ray study of the Geminga pulsar with NuSTAR and XMM-Newton

DEFF Research Database (Denmark)

Mori, Kaya; Gotthelf, Eric V.; Dufour, Francois

2014-01-01

We report on the first hard X-ray detection of the Geminga pulsar above 10 keV using a 150 ks observation with the Nuclear Spectroscopic Telescope Array (NuSTAR) observatory. The double-peaked pulse profile of non-thermal emission seen in the soft X-ray band persists at higher energies. Broadband......V. The spectral hardening in non-thermal X-ray emission as well as spectral flattening between the optical and X-ray bands argue against the conjecture that a single power law may account for multi-wavelength non-thermal spectra of middle-aged pulsars....

First results from plasma density measurements in the FTU tokamak by means of a two-frequency pulsed time-of-flight refractometer

Energy Technology Data Exchange (ETDEWEB)

Petrov, V. G.; Malyshev, A. Yu.; Markov, V. K.; Petrov, A. A. [Troitsk Institute for Innovation and Fusion Research (Russian Federation); Avino, F.; Angelis, R. de; Tudisco, O. [ENEA-UT Fusione Centro Ricerche Frascati (Italy)

2012-04-15

A pulsed time-of-flight refractometer was developed and tested to determine the mean plasma density in the T-11M tokamak by measuring the propagation time of nanosecond microwave pulses in plasma. Later, it was also proposed to use such an instrument to measure and control the mean plasma density in the ITER tokamak by probing the plasma with an extraordinary wave, the electric field of which is perpendicular to the magnetic field in plasma, in the transparency window at frequencies of 50-100 GHz. To avoid the effect of the density profile shape on the measurement results in the nonlinear mode of refractometer operation (near the cutoff), a system operating at two different probing frequencies was developed and tested. Such a system provides two values of the time delay, which can be used to estimate the peaking factor of the density distribution {alpha} and correctly determine the linear density Left-Pointing-Angle-Bracket Nl Right-Pointing-Angle-Bracket , regardless of the density profile (assuming a smooth density profile of the form of N({rho}) = N(0)(1 - {rho}{sup 2}){sup {alpha}}, where N(0) is the central plasma density and {rho} = r/a is the normalized plasma radius). The first experiments on density measurements in the FTU tokamak performed with this refractometer are described, and results from these experiments are presented. The formation of a thin dense plasma layer in the zone of a strong magnetic field (the so-called MARFE layer) at a relatively low (for FTU) plasma density of {approx}6 Multiplication-Sign 10{sup 19} m{sup -3} was detected. The thickness of this layer, determined from the refractometry data, agrees well with the data obtained using a digital camera.

Pulse coil concepts for the LCP Facility

International Nuclear Information System (INIS)

Nelson, B.E.; Burn, P.B.

1977-01-01

The pulse coils described in this paper are resistive copper magnets driven by time-varying currents. They are included in the Large Coil Test Facility (LCTF) portion of the Large Coil Program (LCP) to simulate the pulsed field environment of the toroidal coils in a tokamak reactor. Since TNS (a 150 sec, 5MA, igniting tokamak) and the Oak Ridge EPR (Experimental Power Reactor) are representative of the first tokamaks to require the technology developed in LCP, the reference designs for these machines, especially TNS, are used to derive the magnetic criteria for the pulse coils. This criteria includes the magnitude, distribution, and rate of change of pulsed fields in the toroidal coil windings. Three pulse coil concepts are evaluated on the basis of magnetic criteria and factors such as versatility of design, ease of fabrication and cost of operation. The three concepts include (1) a pair of poloidal coils outside the LCTF torus, (2) a single poloidal coil threaded through the torus, and (3) a pair of vertical axis coil windings inside the bore of one or more of the toroidal test coils

Using HAWC to discover invisible pulsars

Energy Technology Data Exchange (ETDEWEB)

Linden, Tim; Auchettl, Katie; Bramante, Joseph; Cholis, Ilias; Fang, Ke; Hooper, Dan; Karwal, Tanvi; Li, Shirley Weishi

2017-11-01

Observations by HAWC and Milagro have detected bright and spatially extended TeV gamma-ray sources surrounding the Geminga and Monogem pulsars. We argue that these observations, along with a substantial population of other extended TeV sources coincident with pulsar wind nebulae, constitute a new morphological class of spatially extended TeV halos. We show that HAWCs wide field-of-view unlocks an expansive parameter space of TeV halos not observable by atmospheric Cherenkov telescopes. Under the assumption that Geminga and Monogem are typical middle-aged pulsars, we show that ten-year HAWC observations should eventually observe 37$^{+17}_{-13}$ middle-aged TeV halos that correspond to pulsars whose radio emission is not beamed towards Earth. Depending on the extrapolation of the TeV halo efficiency to young pulsars, HAWC could detect more than 100 TeV halos from mis-aligned pulsars. These pulsars have historically been difficult to detect with existing multiwavelength observations. TeV halos will constitute a significant fraction of all HAWC sources, allowing follow-up observations to efficiently find pulsar wind nebulae and thermal pulsar emission. The observation and subsequent multi-wavelength follow-up of TeV halos will have significant implications for our understanding of pulsar beam geometries, the evolution of PWN, the diffusion of cosmic-rays near energetic pulsars, and the contribution of pulsars to the cosmic-ray positron excess.

A search for extragalactic pulsars in the local group galaxies IC 10 and Barnard’s galaxy

International Nuclear Information System (INIS)

Al Noori, H; Roberts, M S E; Champion, D; McLaughlin, M; Ransom, Scott; Ray, P S

2017-01-01

As of today, more than 2500 pulsars have been found, nearly all in the Milky Way, with the exception of ∼28 pulsars in the Small and Large Magellanic Clouds. However, there have been few published attempts to search for pulsars deeper in our Galactic neighborhood. Two of the more promising Local Group galaxies are IC 10 and NGC 6822 (also known as Barnard’s Galaxy) due to their relatively high star formation rate and their proximity to our galaxy. IC 10 in particular, holds promise as it is the closest starburst galaxy to us and harbors an unusually high number of Wolf-Rayet stars, implying the presence of many neutron stars. We observed IC 10 and NGC 6822 at 820 MHz with the Green Bank Telescope for ∼15 and 5 hours respectively, and put a strong upper limit of 0.1 mJy on pulsars in either of the two galaxies. We also performed single pulse searches of both galaxies with no firm detections. (paper)

The galactic distribution of pulsars

International Nuclear Information System (INIS)

Lyne, A.G.

1982-01-01

The galactic distribution of pulsars follows the general form of many population I objects in galactocentric radius, but has a wide distribution above and below the plane due to high space velocities imparted to the pulsars at birth. Statistical studies of the properties of large numbers of pulsars and proper motion measurements demonstrate that the effective magnetic dipole moments decay on a timescale of about 8 million years. This work provides a better knowledge of pulsar evolution and ages and shows that a birthrate of one pulsar every 20 to 50 years is required to sustain the observed galactic population of 300,000. This rate is comparable with most recent estimates of the galactic supernova rate, but requires nearly all supernovae to produce active pulsars. (orig.)

Radioastronomie d'amateur, détection de pulsars a 21 cm

Science.gov (United States)

Maintoux, Jean-Jacques

2017-01-01

Since the discovery of PSR B1919+21 in 1967, the study of radio pulsars has been so far the work of professional teams using large aperture arrays or single dish antennas. While the discovery of new pulsars is so far out of reach of amateurs astronomers with limited resources, we report the successful detection of 3 pulsars at 1420MHz with a 3.3m prime focus dish antenna, namely: B0329+54, B0950+08 and B1133+16. According to the Neutron Star list [6], this sets a new detection record given the very limited aperture of the antenna. In this paper, we expose how the sensibility and stability to achieve such detection was obtained with our constrained setup, then we discuss the data processing aspects, including the period calculation and folding for each PSR, as well as pulse profiles. With the upcoming upgrades to the telescope, more detections are likely to come. An ongoing observation of B2020+28 already yields promising results. Follow the last results here : http://www.f1ehn.org "radioastro"

The scientific program of the Tokamak de Varennes

International Nuclear Information System (INIS)

Daughney, C.C.

1989-01-01

The Tokamak de Varennes (TdeV) is the principal research tool of the Centre canadien de fusion magnetique (CCFM). This article places the Tokamak de Varennes within the framework of the Canadian National Fusion Program (NFP) and describes the scientific program of the TdeV as it was presented at the April 1989 meeting of the CCFM Advisory Committee. The CCFM scientific plant contains three main elements: tokamak development, research on transport and equilibrium in plasmas, and research on the plasma-wall problem. Phase I of the experimental program, commissioning the tokamak and the diagnostic systems, has been completed. Phase II of the experimental program will begin in December 1989 with the plasma boundary defined by a magnetic divertor and the power supplies and vacuum system capable of creating a sequence of one-second plasma pulses. (3 figs., 3 refs.) (L.L.)

The cryogenic helium cooling system for the Tokamak physics experiment

International Nuclear Information System (INIS)

Felker, B.; Slack, D.S.; Wendland, C.R.

1995-01-01

The Tokamak Physics Experiment (TPX) will use supercritical helium to cool all the magnets and supply helium to the Vacuum cryopumping subsystem. The heat loads will come from the standard steady state conduction and thermal radiation sources and from the pulsed loads of the nuclear and eddy currents caused by the Central Solenoid Coils and the plasma positioning coils. The operations of the TPX will begin with pulses of up to 1000 seconds in duration every 75 minutes. The helium system utilizes a pulse load leveling scheme to buffer out the effects of the pulse load and maintain a constant cryogenic plant operation. The pulse load leveling scheme utilizes the thermal mass of liquid and gaseous helium stored in a remote dewar to absorb the pulses of the tokamak loads. The mass of the stored helium will buffer out the temperature pulses allowing 5 K helium to be delivered to the magnets throughout the length of the pulse. The temperature of the dewar will remain below 5 K with all the energy of the pulse absorbed. This paper will present the details of the heat load sources, of the pulse load leveling scheme operations, a partial helium schematic, dewar temperature as a function of time, the heat load sources as a function of time and the helium temperature as a function of length along the various components that will be cooled

Radio-quiet Gamma-ray Pulsars

Directory of Open Access Journals (Sweden)

Lupin Chun-Che Lin

2016-09-01

Full Text Available A radio-quiet γ-ray pulsar is a neutron star that has significant γ-ray pulsation but without observed radio emission or only limited emission detected by high sensitivity radio surveys. The launch of the Fermi spacecraft in 2008 opened a new epoch to study the population of these pulsars. In the 2nd Fermi Large Area Telescope catalog of γ-ray pulsars, there are 35 (30 % of the 117 pulsars in the catalog known samples classified as radio-quiet γ-ray pulsars with radio flux density (S1400 of less than 30 μJy. Accompanying the observations obtained in various wavelengths, astronomers not only have the opportunity to study the emitting nature of radio-quiet γ-ray pulsars but also have proposed different models to explain their radiation mechanism. This article will review the history of the discovery, the emission properties, and the previous efforts to study pulsars in this population. Some particular cases known as Geminga-like pulsars (e.g., PSR J0633+1746, PSR J0007+7303, PSR J2021+4026, and so on are also to specified discuss their common and specific features.

New limits on the population of normal and millisecond pulsars in the Large and Small Magellanic Clouds

Science.gov (United States)

Ridley, J. P.; Lorimer, D. R.

2010-07-01

We model the potentially observable populations of normal and millisecond radio pulsars in the Large and Small Magellanic Clouds (LMC and SMC, respectively) where the known population currently stands at 19 normal radio pulsars. Taking into account the detection thresholds of previous surveys, and assuming optimal period and luminosity distributions based on studies of Galactic pulsars, we estimate that there are (1.79 +/- 0.20) × 104 and (1.09 +/- 0.16) × 104 normal pulsars in the LMC and SMC, respectively. When we attempt to correct for beaming effects, and the fraction of high-velocity pulsars which escape the clouds, we estimate birth rates in both the LMC and SMC to be comparable and in the range of 0.5-1 pulsars per century. Although higher than estimates for the rate of core-collapse supernovae in the clouds, these pulsar birth rates are consistent with historical supernova observations in the past 300 yr. A substantial population of active radio pulsars (of the order of a few hundred thousand) has escaped the LMC and SMC and populates the local intergalactic medium. For the millisecond pulsar (MSP) population, the lack of any detections from current surveys leads to respective upper limits (at the 95 per cent confidence level) of 15000 for the LMC and 23000 for the SMC. Several MSPs could be detected by a currently ongoing survey of the SMC with improved time and frequency resolution using the Parkes multibeam system. Giant-pulse emitting neutron stars could also be seen by this survey.

Variations of the harmonic components of the X-ray pulse profile of PSR B1509–58

International Nuclear Information System (INIS)

Pradhan Pragati; Paul Biswajit; Raichur Harsha; Paul Bikash Chandra

2015-01-01

We used the Fourier decomposition technique to investigate the stability of the X-ray pulse profile of a young pulsar PSR B1509–58 by studying the relative amplitudes and phase differences of its harmonic components with respect to the fundamental using data from the Rossi X-Ray Timing Explorer. Like most young rotation powered pulsars, PSR B1509–58 has a high spin down rate. It also has less timing noise, allowing accurate measurement of higher order frequency derivatives which in turn helps in the study of the physics of pulsar spin down. Detailed investigation of pulse profiles over the years will help us establish any possible connection between the timing characteristics and the high energy emission characteristics for this pulsar. Furthermore, the study of pulse profiles of short period X-ray pulsars can also be useful when used as a means of interplanetary navigation. The X-ray pulse profile of this source has been analyzed for 15 yr (1996–2011). The long term average amplitudes of the first, second and third harmonics (and their standard deviation for individual measurements) compared to the fundamental are 36.9% (1.7%), 13.4% (1.9%) and 9.4% (1.8%) respectively. Similarly, the phases of the three harmonics (and standard deviations) with respect to the fundamental are 0.36 (0.06), 1.5 (0.2) and 2.5 (0.3) radian respectively. We do not find any significant variation of the harmonic components of the pulse profile in comparison to the fundamental. (research papers)

Steady State versus Pulsed Tokamak DEMO

Energy Technology Data Exchange (ETDEWEB)

Orsitto, F.P., E-mail: francesco.orsitto@enea.it [Associazione EURATOM-ENEA Unita Tecnica Fusione, Frascati (Italy); Todd, T. [CCFE/Fusion Association, Culham Science Centre, Abingdon (United Kingdom)

2012-09-15

Full text: The present report deals with a Review of problems for a Steady state(SS) DEMO, related argument is treated about the models and the present status of comparison between the characteristics of DEMO pulsed versus a Steady state device.The studied SS DEMO Models (SLIM CS, PPCS model C EU-DEMO, ARIES-RS) are analyzed from the point of view of the similarity scaling laws and critical issues for a steady state DEMO. A comparison between steady state and pulsed DEMO is therefore carried out: in this context a new set of parameters for a pulsed (6 - 8 hours pulse) DEMO is determined working below the density limit, peak temperature of 20 keV, and requiring a modest improvement in the confinement factor(H{sub IPBy2} = 1.1) with respect to the H-mode. Both parameters density and confinement parameter are lower than the DEMO models presently considered. The concept of partially non-inductive pulsed DEMO is introduced since a pulsed DEMO needs heating and current drive tools for plasma stability and burn control. The change of the main parameter design for a DEMO working at high plasma peak temperatures T{sub e} {approx} 35 keV is analyzed: in this range the reactivity increases linearly with temperature, and a device with smaller major radius (R = 7.5 m) is compatible with high temperature. Increasing temperature is beneficial for current drive efficiency and heat load on divertor, being the synchrotron radiation one of the relevant components of the plasma emission at high temperatures and current drive efficiency increases with temperature. Technology and engineering problems are examined including efficiency and availability R&D issues for a high temperature DEMO. Fatigue and creep-fatigue effects of pulsed operations on pulsed DEMO components are considered in outline to define the R&D needed for DEMO development. (author)

Gas blanket fueling of a tokamak reactor

International Nuclear Information System (INIS)

Gralnick, S.L.

1978-01-01

The purpose of this paper is a speculative investigation of the potential of fueling a Tokamak by introducing a sufficiently large quantity of gaseous deuterium and tritium at the vacuum wall boundary. It is motivated by two factors: current generation tokamaks are, in a manner of speaking, fueled from the edge quite successfully as is evidenced by pulse lengths that are long compared to particle recycling times, and by rapid plasma density increase produced by gas puffing, alternative, deep penetration fueling techniques that have been proposed possess severe technological problems and large costs

Study of the high energy gamma-ray emission from the crab pulsar with the MAGIC telescope and Fermi-LAT

International Nuclear Information System (INIS)

Saito, Takayuki

2010-01-01

My thesis deals with a fundamental question of high energy gamma-ray astronomy. Namely, I studied the cut-off shape of the Crab pulsar spectrum to distinguish between the leading scenarios for the pulsar models. Pulsars are celestial objects, which emit periodic pulsed electromagnetic radiation (pulsation) from radio to high energy gamma-rays. Two major scenarios evolved in past 40 years to explain the pulsation mechanism: the inner magnetosphere scenario and the outer magnetosphere scenario. Both scenarios predict a high energy cut-off in the gamma-ray energy spectrum, but with different cut-off sharpness. An exponential cut-off is expected for the outer magnetosphere scenario while a super-exponential cut-off is predicted for the inner magnetosphere scenario. Therefore, one of the best ways to confirm or refute these scenarios is to measure the energy spectrum of a pulsar at around the cut-off energy, i.e., at energies between a few GeV and a few tens of GeV. All past attempts to measure pulsar spectra with ground-based instruments have failed while satellite-borne detectors had a too small area to study detailed spectra in the GeV domain. In this thesis, the gamma-ray emission at around the cut-off energy from the Crab pulsar is studied with the MAGIC telescope. The public data of the satellite-borne gamma-ray detector, Fermi-LAT, are also analyzed in order to discuss the MAGIC observation results in comparison with the adjacent energy band. In late 2007, a new trigger system (SUM trigger system) allowed to reduce the threshold energy of the MAGIC telescope from 50 GeV to 25 GeV and the Crab pulsar was successfully detected during observations from October 2007 and January 2009. My analysis reveals that the energy spectrum is consistent with a simple power law between 25 GeV to 100 GeV. The extension of the energy spectrum up to 100 GeV rules out the inner magnetosphere scenario. Fermi-LAT started operation in August 2008. The Fermi-LAT data reveal that a power

Study of the high energy gamma-ray emission from the crab pulsar with the MAGIC telescope and Fermi-LAT

Energy Technology Data Exchange (ETDEWEB)

Saito, Takayuki

2010-12-06

My thesis deals with a fundamental question of high energy gamma-ray astronomy. Namely, I studied the cut-off shape of the Crab pulsar spectrum to distinguish between the leading scenarios for the pulsar models. Pulsars are celestial objects, which emit periodic pulsed electromagnetic radiation (pulsation) from radio to high energy gamma-rays. Two major scenarios evolved in past 40 years to explain the pulsation mechanism: the inner magnetosphere scenario and the outer magnetosphere scenario. Both scenarios predict a high energy cut-off in the gamma-ray energy spectrum, but with different cut-off sharpness. An exponential cut-off is expected for the outer magnetosphere scenario while a super-exponential cut-off is predicted for the inner magnetosphere scenario. Therefore, one of the best ways to confirm or refute these scenarios is to measure the energy spectrum of a pulsar at around the cut-off energy, i.e., at energies between a few GeV and a few tens of GeV. All past attempts to measure pulsar spectra with ground-based instruments have failed while satellite-borne detectors had a too small area to study detailed spectra in the GeV domain. In this thesis, the gamma-ray emission at around the cut-off energy from the Crab pulsar is studied with the MAGIC telescope. The public data of the satellite-borne gamma-ray detector, Fermi-LAT, are also analyzed in order to discuss the MAGIC observation results in comparison with the adjacent energy band. In late 2007, a new trigger system (SUM trigger system) allowed to reduce the threshold energy of the MAGIC telescope from 50 GeV to 25 GeV and the Crab pulsar was successfully detected during observations from October 2007 and January 2009. My analysis reveals that the energy spectrum is consistent with a simple power law between 25 GeV to 100 GeV. The extension of the energy spectrum up to 100 GeV rules out the inner magnetosphere scenario. Fermi-LAT started operation in August 2008. The Fermi-LAT data reveal that a power

Radio pulsar death lines to SGRs/AXPs and white dwarfs pulsars

Energy Technology Data Exchange (ETDEWEB)

Lobato, Ronaldo V.; Malheiro, M. [Departamento de Física, Instituto Tecnológico de Aeronáutica, ITA - DCTA, Vila das Acácias, São José dos Campos, 12228-900 SP (Brazil); Coelho, J. G. [INPE - Instituto Nacional de Pesquisas Espaciais, Divisão de Astrofísica, Av. dos Astronautas 1758, São José dos Campos, 12227-010 SP (Brazil)

2015-12-17

Recently, an alternative model based on white dwarfs pulsars has been proposed to explain a class of pulsars known as Soft Gamma Repeaters (SGR) and Anomalus X-Ray Pulsars (AXP) [1], usually named as magnetars. In this model, the magnetized white dwarfs can have surface magnetic field B ∼ 10{sup 7} − 10{sup 10} G and rotate very fast with angular frequencies Ω ∼ 1 rad/s, allowing them to produce large electromagnetic (EM) potentials and generate electron-positron pairs. These EM potentials are comparable with the ones of neutron star pulsars with strong magnetic fields and even larger. In this study we consider two possible processes associated with the particle acceleration, both of them are common used to explain radio emission in neutron star pulsars: in the first process the pair production happens near to the star polar caps, i.e. inside of the light cylinder where magnetic field lines are closed; in the second one the creation of pair happens in the outer magnetosphere, i.e. far away of the star surface where magnetic field lines are open [2]. The analysis of the possibility of radio emission were done for 23 SGRs/AXPs of the McGill Online Magnetar Catalog [3] that contains the current information available on these sources. The results of this work show that the model where the particles production occur in the outer magnetosphere emission “o2” is the process compatible with the astronomical observations of absence of radio emission for almost all SGRs/AXPs when these sources are understood as white dwarf pulsars. Our work is a first attempted to find an explanation for the puzzle why for almost all the SGRs/AXPs was expected radio emission, but it was observed in only four of them. These four sources, as it was suggested recently [4], seem to belong to an high magnetic field neutron star pulsar category, different from all the others SGRs/AXPs that our work indicate to belong to a new class of white dwarf pulsars, very fast and magnetized.

LOFAR Discovery of the Fastest-spinning Millisecond Pulsar in the Galactic Field

Science.gov (United States)

Bassa, C. G.; Pleunis, Z.; Hessels, J. W. T.; Ferrara, E. C.; Breton, R. P.; Gusinskaia, N. V.; Kondratiev, V. I.; Sanidas, S.; Nieder, L.; Clark, C. J.; Li, T.; van Amesfoort, A. S.; Burnett, T. H.; Camilo, F.; Michelson, P. F.; Ransom, S. M.; Ray, P. S.; Wood, K.

2017-09-01

We report the discovery of PSR J0952-0607, a 707 Hz binary millisecond pulsar that is now the fastest-spinning neutron star known in the Galactic field (I.e., outside of a globular cluster). PSR J0952-0607 was found using LOFAR at a central observing frequency of 135 MHz, well below the 300 MHz to 3 GHz frequencies typically used in pulsar searches. The discovery is part of an ongoing LOFAR survey targeting unassociated Fermi-Large Area Telescope γ-ray sources. PSR J0952-0607 is in a 6.42 hr orbit around a very low-mass companion ({M}{{c}}≳ 0.02 {M}⊙ ), and we identify a strongly variable optical source, modulated at the orbital period of the pulsar, as the binary companion. The light curve of the companion varies by 1.6 mag from {r}{\\prime }=22.2 at maximum to {r}{\\prime }> 23.8, indicating that it is irradiated by the pulsar wind. Swift observations place a 3σ upper limit on the 0.3-10 {keV} X-ray luminosity of {L}Xdispersion measure). Though no eclipses of the radio pulsar are observed, the properties of the system classify it as a black widow binary. The radio pulsed spectrum of PSR J0952-0607, as determined through flux density measurements at 150 and 350 MHz, is extremely steep with α ˜ -3 (where S\\propto {ν }α ). We discuss the growing evidence that the fastest-spinning radio pulsars have exceptionally steep radio spectra, as well as the prospects for finding more sources like PSR J0952-0607.

Pulsar emission amplified and resolved by plasma lensing in an eclipsing binary.

Science.gov (United States)

Main, Robert; Yang, I-Sheng; Chan, Victor; Li, Dongzi; Lin, Fang Xi; Mahajan, Nikhil; Pen, Ue-Li; Vanderlinde, Keith; van Kerkwijk, Marten H

2018-05-01

Radio pulsars scintillate because their emission travels through the ionized interstellar medium along multiple paths, which interfere with each other. It has long been realized that, independent of their nature, the regions responsible for the scintillation could be used as 'interstellar lenses' to localize pulsar emission regions 1,2 . Most such lenses, however, resolve emission components only marginally, limiting results to statistical inferences and detections of small positional shifts 3-5 . As lenses situated close to their source offer better resolution, it should be easier to resolve emission regions of pulsars located in high-density environments such as supernova remnants 6 or binaries in which the pulsar's companion has an ionized outflow. Here we report observations of extreme plasma lensing in the 'black widow' pulsar, B1957+20, near the phase in its 9.2-hour orbit at which its emission is eclipsed by its companion's outflow 7-9 . During the lensing events, the observed radio flux is enhanced by factors of up to 70-80 at specific frequencies. The strongest events clearly resolve the emission regions: they affect the narrow main pulse and parts of the wider interpulse differently. We show that the events arise naturally from density fluctuations in the outer regions of the outflow, and we infer a resolution of our lenses that is comparable to the pulsar's radius, about 10 kilometres. Furthermore, the distinct frequency structures imparted by the lensing are reminiscent of what is observed for the repeating fast radio burst FRB 121102, providing observational support for the idea that this source is observed through, and thus at times strongly magnified by, plasma lenses 10 .

Formation and sustainment of a low aspect ratio tokamak by a series of plasma injections

International Nuclear Information System (INIS)

Shimamura, Shin; Taniguchi, Makoto; Takahashi, Tsutomu; Nogi, Yasuyuki

1995-01-01

A low aspect ratio tokamak plasma was generated and sustained by injecting a series of plasmas from a magnetized coaxial gun into a flux conserver with toroidal field. The magnetized coaxial gun was supplied by an oscillating current with a d.c. component. The first few current pulses injected plasma and helicity into the flux conserver. This pulse helicity injection method worked effectively to maintain the low aspect ratio tokamak. 8 refs., 5 figs

DEEP X-RAY OBSERVATIONS OF THE YOUNG HIGH-MAGNETIC-FIELD RADIO PULSAR J1119-6127 AND SUPERNOVA REMNANT G292.2-0.5

Energy Technology Data Exchange (ETDEWEB)

Ng, C.-Y.; Kaspi, V. M. [Department of Physics, McGill University, Montreal, QC H3A 2T8 (Canada); Ho, W. C. G. [School of Mathematics, University of Southampton, Southampton SO17 1BJ (United Kingdom); Weltevrede, P. [Jodrell Bank Centre for Astrophysics, University of Manchester, Alan Turing Building, Manchester M13 9PL (United Kingdom); Bogdanov, S. [Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Shannon, R. [CSIRO Astronomy and Space Sciences, Australia Telescope National Facility, Marsfield, NSW 2210 (Australia); Gonzalez, M. E., E-mail: ncy@physics.mcgill.ca [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1 (Canada)

2012-12-10

High-magnetic-field radio pulsars are important transition objects for understanding the connection between magnetars and conventional radio pulsars. We present a detailed study of the young radio pulsar J1119-6127, which has a characteristic age of 1900 yr and a spin-down-inferred magnetic field of 4.1 Multiplication-Sign 10{sup 13} G, and its associated supernova remnant G292.2-0.5, using deep XMM-Newton and Chandra X-ray Observatory exposures of over 120 ks from each telescope. The pulsar emission shows strong modulation below 2.5 keV with a single-peaked profile and a large pulsed fraction of 0.48 {+-} 0.12. Employing a magnetic, partially ionized hydrogen atmosphere model, we find that the observed pulse profile can be produced by a single hot spot of temperature 0.13 keV covering about one-third of the stellar surface, and we place an upper limit of 0.08 keV for an antipodal hot spot with the same area. The non-uniform surface temperature distribution could be the result of anisotropic heat conduction under a strong magnetic field, and a single-peaked profile seems common among high-B radio pulsars. For the associated remnant G292.2-0.5, its large diameter could be attributed to fast expansion in a low-density wind cavity, likely formed by a Wolf-Rayet progenitor, similar to two other high-B radio pulsars.

Digital controlled pulsed electric system of the ETE tokamak. First report; Sistema eletrico pulsado com controle digital do Tokamak ETE (experimento Tokamak esferico). Primeiro relatorio

Energy Technology Data Exchange (ETDEWEB)

Barbosa, Luis Felipe de F.P.W.; Del Bosco, Edson

1997-12-31

This reports presents a summary on the thermonuclear fusion and application for energy supply purposes. The tokamak device operation and the magnetic field production systems are described. The ETE tokamak is a small aspect ratio device designed for plasma physics and thermonuclear fusion studies, which presently is under construction at the Laboratorio Associado de Plasma (LAP), Instituto Nacional de Pesquisas Espaciais (INPE) - S.J. dos Campos - S. Paulo. (author) 55 refs., 40 figs.

Digital controlled pulsed electric system of the ETE tokamak. First report; Sistema eletrico pulsado com controle digital do Tokamak ETE (experimento Tokamak esferico). Primeiro relatorio

Energy Technology Data Exchange (ETDEWEB)

Barbosa, Luis Felipe de F.P.W.; Del Bosco, Edson

1998-12-31

This reports presents a summary on the thermonuclear fusion and application for energy supply purposes. The tokamak device operation and the magnetic field production systems are described. The ETE tokamak is a small aspect ratio device designed for plasma physics and thermonuclear fusion studies, which presently is under construction at the Laboratorio Associado de Plasma (LAP), Instituto Nacional de Pesquisas Espaciais (INPE) - S.J. dos Campos - S. Paulo. (author) 55 refs., 40 figs.

Axion mass limits from pulsar x rays

International Nuclear Information System (INIS)

Morris, D.E.

1984-12-01

Axions thermally emitted by a neutron star would be converted into x rays in the strong magnetic field surrounding the star. An improvement in the observational upper limit of pulsed x rays from the Vela pulsar (PSR 0833-45) by a factor of 12 would constrain the axion mass M/sub a/ -3 eV if the core is non-superfluid and at temperature T/sub c/ greater than or equal to 2 x 10 8 K. If the core is superfluid throughout, an improvement factor of 240 would be needed to provide the same constraint on the axion mass, while in the absence of superfluidity, an improvement factor of 200 could constrain M/sub a/ -4 eV. A search for modulated hard x rays from PSR 1509-58 or other young pulsars at presently attainable sensitivities may enable the setting of an upper limit for the axion mass. Observation of hard x rays from a very young hot pulsar with T/sub c/ greater than or equal to 7 x 10 8 K could set a firm bound on the axion mass, since neutron superfluidity is not expected above this temperature. The remaining axion mass range 6 x 10 -4 eV > M/sub a/ > 10 -5 eV (the cosmological lower bound) can be covered by an improved Sikivie type laboratory cavity detector for relic axions constituting the galactic halo. 48 refs

Options for an ignited tokamak

International Nuclear Information System (INIS)

Sheffield, J.

1984-02-01

It is expected that the next phase of the fusion program will involve a tokamak with the goals of providing an ignited plasma for pulses of hundreds of seconds. A simple model is described in this memorandum which establishes the physics conditions for such a self-sustaining plasma, for given ion and electron thermal diffusivities, in terms of R/a, b/a, I, B/q, epsilon β/sub p/, anti T/sub i/, and anti T/sub e//anti T/sub i/. The model is used to produce plots showing the wide range of tokamaks that may ignite or have a given ignition margin. The constraints that limit this range are discussed

Recent designs for advanced fusion reactor blankets

International Nuclear Information System (INIS)

Sze, D.K.

1994-06-01

A series of reactor design studies based on the Tokamak configuration have been carried out under the direction of Professor Robert Conn of UCLA. They are called ARIES-1 through 4 and PULSAR 1 and 2. The key mission of these studies is to evaluate the attractiveness of fusion assuming different degrees of advancement in either physics or engineering development. Also, the requirements of engineering and physics systems for a pulsed reactor were evaluated by the PULSAR design studies. This paper discusses the directions and conclusions of the blanket and related engineering systems for those design studies

Automation of Aditya tokamak plasma position control DC power supply

Energy Technology Data Exchange (ETDEWEB)

Arambhadiya, Bharat, E-mail: bharat@ipr.res.in; Raj, Harshita; Tanna, R.L.; Edappala, Praveenlal; Rajpal, Rachana; Ghosh, Joydeep; Chattopadhyay, P.K.; Kalal, M.B.

2016-11-15

Highlights: • Plasma position control is very essential for obtaining repeatable high temperature, high-density discharges of longer durations in tokomak. • The present capacitor bank has limitations of maximum current capacity and position control beyond 200 ms. • The installation of a separate set of coils and a DC power supply can control the plasma position beyond 200 ms. • A high power thyristor (T588N1200) triggers for DC current pulse of 300 A fires precisely at required positions to modify plasma position. • The commissioning is done for the automated in-house, quick and reliable solution. - Abstract: Plasma position control is essential for obtaining repeatable high temperature, high-density discharges of longer duration in tokamaks. Recently, a set of external coils is installed in the vertical field mode configuration to control the radial plasma position in ADITYA tokamak. The existing capacitor bank cannot provide the required current pulse beyond 200 ms for position control. This motivated to have a DC power supply of 500 A to provide current pulse beyond 200 ms for the position control. The automatization of the DC power supply mandated interfaces with the plasma control system, Aditya Pulse Power supply, and Data acquisition system for coordinated discharge operation. A high current thyristor circuit and a timer circuit have been developed for controlling the power supply automatically for charging vertical field coils of Aditya tokamak. Key protection interlocks implemented in the development ensure machine and occupational safety. Fiber-optic trans-receiver isolates the power supply with other subsystems, while analog channel is optically isolated. Commissioning and testing established proper synchronization of the power supply with tokamak operation. The paper discusses the automation of the DC power supply with main circuit components, timing control, and testing results.

Magnet design considerations for Tokamak fusion reactors

International Nuclear Information System (INIS)

Purcell, J.R.; Chen, W.; Thomas, R.

1976-01-01

Design problems for superconducting ohmic heating and toroidal field coils for large Tokamak fusion reactors are discussed. The necessity for making these coils superconducting is explained, together with the functions of these coils in a Tokamak reactor. Major problem areas include materials related aspects and mechanical design and cryogenic considerations. Projections and comparisons are made based on existing superconducting magnet technology. The mechanical design of large-scale coils, which can contain the severe electromagnetic loading and stress generated in the winding, are emphasized. Additional major tasks include the development of high current conductors for pulsed applications to be used in fabricating the ohmic heating coils. It is important to note, however, that no insurmountable technical barriers are expected in the course of developing superconducting coils for Tokamak fusion reactors. (Auth.)

The prospects of pulsar timing with new-generation radio telescopes and the Square Kilometre Array

Science.gov (United States)

Stappers, B. W.; Keane, E. F.; Kramer, M.; Possenti, A.; Stairs, I. H.

2018-05-01

Pulsars are highly magnetized and rapidly rotating neutron stars. As they spin, the lighthouse-like beam of radio emission from their magnetic poles sweeps across the Earth with a regularity approaching that of the most precise clocks known. This precision combined with the extreme environments in which they are found, often in compact orbits with other neutron stars and white dwarfs, makes them excellent tools for studying gravity. Present and near-future pulsar surveys, especially those using the new generation of telescopes, will find more extreme binary systems and pulsars that are more precise `clocks'. These telescopes will also greatly improve the precision to which we can measure the arrival times of the pulses. The Square Kilometre Array will revolutionize pulsar searches and timing precision. The increased number of sources will reveal rare sources, including possibly a pulsar-black hole binary, which can provide the most stringent tests of strong-field gravity. The improved timing precision will reveal new phenomena and also allow us to make a detection of gravitational waves in the nanohertz frequency regime. It is here where we expect to see the signature of the binary black holes that are formed as galaxies merge throughout cosmological history. This article is part of a discussion meeting issue `The promises of gravitational-wave astronomy'.

Pulsar-driven Jets In Supernovae, LMXBs, SS 433, And The Universe

Science.gov (United States)

Middleditch, John

2011-01-01

The model of pulsar emission through superluminally induced polarization currents (SLIP) predicts that pulsations produced by such currents, induced at many light cylinder radii by a rotating, magnetized body, as would be the case for a neutron star born within any star of more than 1.4 solar masses, will drive pulsations close to the axis of rotation. In SN 1987A, such highly collimated (pulsars with very sharp single pulses have been detected because the Earth is in a favored direction where their fluxes diminish only as 1/distance, and this has been verified in the laboratory as well as for the Parkes Multibeam Survey. The axially driven pulsations enforce a toroidal geometry onto all early SNRs, rendering even SNe Ia unsuitable as standard candles. SLIP also specifically predicts that gamma-ray-burst afterglows will be essentially 100% pulsed at 500 Hz in their proper frame. Finally, SLIP jets from SNe of the first stars may allow galaxies to form without the need for dark matter. This work was supported in part by the Department of Energy through the Los Alamos Directed Research Grant DR20080085.

WHY ARE PULSAR PLANETS RARE?

Energy Technology Data Exchange (ETDEWEB)

Martin, Rebecca G.; Livio, Mario; Palaniswamy, Divya [Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154 (United States)

2016-12-01

Pulsar timing observations have revealed planets around only a few pulsars. We suggest that the rarity of these planets is due mainly to two effects. First, we show that the most likely formation mechanism requires the destruction of a companion star. Only pulsars with a suitable companion (with an extreme mass ratio) are able to form planets. Second, while a dead zone (a region of low turbulence) in the disk is generally thought to be essential for planet formation, it is most probably rare in disks around pulsars, because of the irradiation from the pulsar. The irradiation strongly heats the inner parts of the disk, thus pushing the inner boundary of the dead zone out. We suggest that the rarity of pulsar planets can be explained by the low probability for these two requirements to be satisfied: a very low-mass companion and a dead zone.

THE GREEN BANK TELESCOPE 350 MHz DRIFT-SCAN SURVEY. I. SURVEY OBSERVATIONS AND THE DISCOVERY OF 13 PULSARS

Energy Technology Data Exchange (ETDEWEB)

Boyles, J.; Lorimer, D. R.; McLaughlin, M. A.; Cardoso, R. F. [Department of Physics, West Virginia University, Morgantown, WV 26506 (United States); Lynch, R. S.; Kaspi, V. M.; Archibald, A.; Karako-Argaman, C. [Department of Physics, McGill University, 3600 University St., Montreal, Quebec, H3A 2T8 (Canada); Ransom, S. M. [National Radio Astronomy Observatory (NRAO), 520 Edgemont Road, Charlottesville, VA 22901 (United States); Stairs, I. H.; Berndsen, A.; Cherry, A.; McPhee, C. A. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1 (Canada); Hessels, J. W. T.; Kondratiev, V. I.; Van Leeuwen, J. [ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo (Netherlands); Epstein, C. R. [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); Pennucci, T. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Roberts, M. S. E. [Eureka Scientific, 2452 Delmer Street, Suite 100, Oakland, CA 94602-3017 (United States); Stovall, K., E-mail: jason.boyles@wku.edu [Center for Advanced Radio Astronomy and Department of Physics and Astronomy, University of Texas at Brownsville, Brownsville, TX 78520 (United States)

2013-02-15

Over the summer of 2007, we obtained 1191 hr of 'drift-scan' pulsar search observations with the Green Bank Telescope at a radio frequency of 350 MHz. Here we describe the survey setup, search procedure, and the discovery and follow-up timing of 13 pulsars. Among the new discoveries, one (PSR J1623-0841) was discovered only through its single pulses, two (PSRs J1327-0755 and J1737-0814) are millisecond pulsars, and another (PSR J2222-0137) is a mildly recycled pulsar. PSR J1327-0755 is a 2.7 ms pulsar at a dispersion measure (DM) of 27.9 pc cm{sup -3} in an 8.7 day orbit with a minimum companion mass of 0.22 M {sub Sun }. PSR J1737-0814 is a 4.2 ms pulsar at a DM of 55.3 pc cm{sup -3} in a 79.3 day orbit with a minimum companion mass of 0.06 M {sub Sun }. PSR J2222-0137 is a 32.8 ms pulsar at a very low DM of 3.27 pc cm{sup -3} in a 2.4 day orbit with a minimum companion mass of 1.11 M {sub Sun }. It is most likely a white-dwarf-neutron-star system or an unusual low-eccentricity double neutron star system. Ten other pulsars discovered in this survey are reported in the companion paper Lynch et al.

Millisecond radio pulsars in globular clusters

Science.gov (United States)

Verbunt, Frank; Lewin, Walter H. G.; Van Paradijs, Jan

1989-01-01

It is shown that the number of millisecond radio pulsars, in globular clusters, should be larger than 100, applying the standard scenario that all the pulsars descend from low-mass X-ray binaries. Moreover, most of the pulsars are located in a small number of clusters. The prediction that Teran 5 and Liller 1 contain at least about a dozen millisecond radio pulsars each is made. The observations of millisecond radio pulsars in globular clusters to date, in particular the discovery of two millisecond radio pulsars in 47 Tuc, are in agreement with the standard scenario, in which the neutron star is spun up during the mass transfer phase.

40 Years of Pulsars: The Birth and Evolution of Isolated Radio Pulsars

OpenAIRE

Faucher-Giguere, C. -A.; Kaspi, V. M.

2007-01-01

We investigate the birth and evolution of isolated radio pulsars using a population synthesis method, modeling the birth properties of the pulsars, their time evolution, and their detection in the Parkes and Swinburne Multibeam (MB) surveys. Together, the Parkes and Swinburne MB surveys have detected nearly 2/3 of the known pulsars and provide a remarkably homogeneous sample to compare with simulations. New proper motion measurements and an improved model of the distribution of free electrons...

The LOFAR Known Pulsar Data Pipeline

NARCIS (Netherlands)

Alexov, A.; Hessels, J.W.T.; Mol, J.D.; Stappers, B.; van Leeuwen, J.

2010-01-01

Abstract: Transient radio phenomena and pulsars are one of six LOFAR Key Science Projects (KSPs). As part of the Transients KSP, the Pulsar Working Group (PWG) has been developing the LOFAR Pulsar Data Pipelines to both study known pulsars as well as search for new ones. The pipelines are being

The green bank northern celestial cap pulsar survey. I. Survey description, data analysis, and initial results

Energy Technology Data Exchange (ETDEWEB)

Stovall, K.; Dartez, L. P.; Ford, A. J.; Garcia, A.; Hinojosa, J.; Jenet, F. A.; Leake, S. [Center for Advanced Radio Astronomy, University of Texas at Brownsville, One West University Boulevard, Brownsville, TX 78520 (United States); Lynch, R. S.; Archibald, A. M.; Karako-Argaman, C.; Kaspi, V. M. [Department of Physics, McGill University, 3600 University Street, Montreal, QC H3A 2T8 (Canada); Ransom, S. M. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22901 (United States); Banaszak, S.; Biwer, C. M.; Day, D.; Flanigan, J.; Kaplan, D. L. [Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211 (United States); Boyles, J. [Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101 (United States); Hessels, J. W. T.; Kondratiev, V. I., E-mail: stovall.kevin@gmail.com [ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo (Netherlands); and others

2014-08-10

We describe an ongoing search for pulsars and dispersed pulses of radio emission, such as those from rotating radio transients (RRATs) and fast radio bursts, at 350 MHz using the Green Bank Telescope. With the Green Bank Ultimate Pulsar Processing Instrument, we record 100 MHz of bandwidth divided into 4096 channels every 81.92 μs. This survey will cover the entire sky visible to the Green Bank Telescope (δ > –40°, or 82% of the sky) and outside of the Galactic Plane will be sensitive enough to detect slow pulsars and low dispersion measure (<30 pc cm{sup –3}) millisecond pulsars (MSPs) with a 0.08 duty cycle down to 1.1 mJy. For pulsars with a spectral index of –1.6, we will be 2.5 times more sensitive than previous and ongoing surveys over much of our survey region. Here we describe the survey, the data analysis pipeline, initial discovery parameters for 62 pulsars, and timing solutions for 5 new pulsars. PSR J0214+5222 is an MSP in a long-period (512 days) orbit and has an optical counterpart identified in archival data. PSR J0636+5129 is an MSP in a very short-period (96 minutes) orbit with a very low mass companion (8 M{sub J}). PSR J0645+5158 is an isolated MSP with a timing residual RMS of 500 ns and has been added to pulsar timing array experiments. PSR J1434+7257 is an isolated, intermediate-period pulsar that has been partially recycled. PSR J1816+4510 is an eclipsing MSP in a short-period orbit (8.7 hr) and may have recently completed its spin-up phase.

Visualization of Pulsar Search Data

Science.gov (United States)

Foster, R. S.; Wolszczan, A.

1993-05-01

The search for periodic signals from rotating neutron stars or pulsars has been a computationally taxing problem to astronomers for more than twenty-five years. Over this time interval, increases in computational capability have allowed ever more sensitive searches, covering a larger parameter space. The volume of input data and the general presence of radio frequency interference typically produce numerous spurious signals. Visualization of the search output and enhanced real-time processing of significant candidate events allow the pulsar searcher to optimally processes and search for new radio pulsars. The pulsar search algorithm and visualization system presented in this paper currently runs on serial RISC based workstations, a traditional vector based super computer, and a massively parallel computer. A description of the serial software algorithm and its modifications for massively parallel computing are describe. The results of four successive searches for millisecond period radio pulsars using the Arecibo telescope at 430 MHz have resulted in the successful detection of new long-period and millisecond period radio pulsars.

Pulsar observations with the MAGIC telescopes

Energy Technology Data Exchange (ETDEWEB)

Garcia, Jezabel R.; Dazzi, F.; Idec, W.; Moretti, E.; Schweizer, T. [Max-Planck-Institut fuer Physik, Munich (Germany); Bonnefoy, S.; Carreto-Fidalgo, D.; Lopez, M. [Universitad Compultense, Madrid (Spain); Galindo, D.; Zanin, R. [Universitat de Barcelona, ICC/IEEC-UB, Barcelona (Spain); Ona Wilhelmi, E. de [Institute for Space Sciences (CSIC/IEEC), Barcelona (Spain); Reichardt, I. [Istituto Nazionale di Fisica Nucleare (INFN), Padova (Italy); Saito, T. [Kyoto University, Hakubi Center (Japan); Collaboration: MAGIC-Collaboration

2016-07-01

MAGIC is a stereoscopic system of two IACTs, located at the ORM (Spain). Since 2008, MAGIC has played a big role in Pulsar physics due to the discovery of the first VHE gamma-ray emission from the Crab pulsar. Such a discovery was possible thanks to a revolutionary trigger technique used in the initial MAGIC mono system, the Sum-Trigger, that provided a 25 GeV energy threshold. The study of the Crab keeps providing numerous important results for the understanding of pulsar physics. The most recent ones are the bridge emission at VHE and the detection of the Crab pulsations at TeV energies. MAGIC has been also searching for new pulsars, providing recently interesting results about the Geminga pulsar and nebula. This talk reviews the essential MAGIC results about VHE pulsars and their implications for pulsar physics.Also we discuss the development of a new stereo trigger system, the Sum-Trigger-II, and the importance of the observation windows that this system opens for the study of VHE pulsars.

A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES

Energy Technology Data Exchange (ETDEWEB)

Yao, J. M.; Wang, N. [Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150, Science 1-Street, Urumqi, Xinjiang 830011 (China); Manchester, R. N. [CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping NSW 1710 (Australia)

2017-01-20

We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H ii regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES

International Nuclear Information System (INIS)

Yao, J. M.; Wang, N.; Manchester, R. N.

2017-01-01

We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H ii regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

Integral luminosities of radio pulsars

Science.gov (United States)

Malov, I.; Malov, O.

The integral radio luminosities L for 311 normal pulsars and for 27 ones with the rotation period Pfalls for fast ones. The mean values of K are -3.73 and -4.85 for normal and fast pulsars, respectively. There are no changes of L with the kinematic age T = z/V, where z is the pulsar height over the Galactic plane and V = 300 km/s is its mean velocity. The correlation between L and the rate of the rotation energy losses E is detected for both pulsar groups under consideration. It is shown that L= A E^(1/3) for the whole sample. The total number of pulsars in the Galaxy and their birth rate are in agreement with data on the rate of supernova explosions.

Pulsar timing and general relativity

Science.gov (United States)

Backer, D. C.; Hellings, R. W.

1986-01-01

Techniques are described for accounting for relativistic effects in the analysis of pulsar signals. Design features of instrumentation used to achieve millisecond accuracy in the signal measurements are discussed. The accuracy of the data permits modeling the pulsar physical characteristics from the natural glitches in the emissions. Relativistic corrections are defined for adjusting for differences between the pulsar motion in its spacetime coordinate system relative to the terrestrial coordinate system, the earth's motion, and the gravitational potentials of solar system bodies. Modifications of the model to allow for a binary pulsar system are outlined, including treatment of the system as a point mass. Finally, a quadrupole model is presented for gravitational radiation and techniques are defined for using pulsars in the search for gravitational waves.

Pulsar signals from relativistic electron beams

International Nuclear Information System (INIS)

Elsaesser, K.; Kirk, J.

1976-01-01

The possibility of the radio emission from pulsars originating in a beam-plasma system is discussed. We calculate the curvature radiation which arises if this system is placed in a very strong curved magnetic field. Numerical experiments show that the beam instability evolves into a rather stationary wave pattern whose Fourier components are concentrated near the most unstable mode. This result leads us to estimates of the radiation intensity of its autocorrelation function in time, and its bandwidth. The results are compared with measurements of the micro-structure of pulses, and the constraints imposed on radiation mechanisms by longer time-scale properties are shown to be satisfied. (orig.) [de

Realizing steady-state tokamak operation for fusion energy

International Nuclear Information System (INIS)

Luce, T. C.

2011-01-01

Continuous operation of a tokamak for fusion energy has clear engineering advantages but requires conditions beyond those sufficient for a burning plasma. The fusion reactions and external sources must support both the pressure and the current equilibrium without inductive current drive, leading to demands on stability, confinement, current drive, and plasma-wall interactions that exceed those for pulsed tokamaks. These conditions have been met individually, and significant progress has been made in the past decade to realize scenarios where the required conditions are obtained simultaneously. Tokamaks are operated routinely without disruptions near pressure limits, as needed for steady-state operation. Fully noninductive sustainment with more than half of the current from intrinsic currents has been obtained for a resistive time with normalized pressure and confinement approaching those needed for steady-state conditions. One remaining challenge is handling the heat and particle fluxes expected in a steady-state tokamak without compromising the core plasma performance.

Gamma ray imager on the DIII-D tokamak

Energy Technology Data Exchange (ETDEWEB)

Pace, D. C., E-mail: pacedc@fusion.gat.com; Taussig, D.; Eidietis, N. W.; Van Zeeland, M. A.; Watkins, M. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Cooper, C. M. [Oak Ridge Associated Universities, Oak Ridge, Tennessee 37830 (United States); Hollmann, E. M. [University of California-San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States); Riso, V. [State University of New York-Buffalo, 12 Capen Hall, Buffalo, New York 14260-1660 (United States)

2016-04-15

A gamma ray camera is built for the DIII-D tokamak [J. Luxon, Nucl. Fusion 42, 614 (2002)] that provides spatial localization and energy resolution of gamma flux by combining a lead pinhole camera with custom-built detectors and optimized viewing geometry. This diagnostic system is installed on the outer midplane of the tokamak such that its 123 collimated sightlines extend across the tokamak radius while also covering most of the vertical extent of the plasma volume. A set of 30 bismuth germanate detectors can be secured in any of the available sightlines, allowing for customizable coverage in experiments with runaway electrons in the energy range of 1–60 MeV. Commissioning of the gamma ray imager includes the quantification of electromagnetic noise sources in the tokamak machine hall and a measurement of the energy spectrum of background gamma radiation. First measurements of gamma rays coming from the plasma provide a suitable testbed for implementing pulse height analysis that provides the energy of detected gamma photons.

Profile correction to electron temperature and enhancement factor in soft-x-ray pulse-height-analysis measurements in tokamaks

International Nuclear Information System (INIS)

Sesnic, S.; Diesso, M.; Hill, K.; Holland, A.; Pohl, F.

1988-01-01

Because soft-x-ray pulse-height-analysis spectra contain chordal information, the electron temperature and the radiation intensity (enhancement factor) measurements do not represent the local values. The correction factors for the electron temperature and the enhancement factor as a function of the temperature and density profile parameters and the energy are obtained. The spectrum distortion due to pulse pileup effects is also evaluated. A set of curves is given from which the distortion of the spectrum can be obtained if the electron temperature, the Be filter thickness, and the electronic parameters of the acquisition system are known. PG 1810,1812 ID 131801CON N X-ray diagnostics TT Profile correction to electron temperature and enhancement factor in soft-x-ray pulse-height-analysis measurements in tokamaks AU S. Sesnic, M. Diesso, K. Hill, and A. Holland LO Princeton University, Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543 AU F. Pohl LO Max-Planck Institut fuer Plasmaphysik, 8046-Garching, Federal Republic of Germany SD (Presented on 16 March 1988) AB Because soft-x-ray pulse-height-analysis spectra contain chordal information, the electron temperature and the radiation intensity (enhancement factor) measurements do not represent the local values. The correction factors for the electron temperature and the enhancement factor as a function of the temperature and density profile parameters and the energy are obtained. The spectrum distortion due to pulse pileup effects is also evaluated. A set of curves is given from which the distortion of the spectrum can be obtained if the electron tempe

Varennes Tokamak

International Nuclear Information System (INIS)

Cumyn, P.B.

A consortium of five organizations under the leadership of IREQ, the Institute de Recherche d'Hydro-Quebec has completed a conceptual design study for a tokamak device, and in January 1981 its construction was authorized with funding being provided principally by Hydro-Quebec and the National Research Council, as well as by the Ministre d'Education du Quebec and Natural Sciences and Engineering Research Council of Canada (NSERC). The device will form the focus of Canada's magnetic-fusion program and will be located in IREQ's laboratories in Varennes. Presently the machine layout is being finalized from the physics point of view and work has started on equipment design and specification. The Tokamak de Varennes will be an experimental device, the purpose of which is to study plasma and other fusion related phenomena. In particular it will study: 1. Plasma impurities and plasma/liner interaction; 2. Long pulse or quasi-continuous operation using plasma rampdown and eventually plasma current reversal in order to maintain the plasma; and 3. Advanced diagnostics

DEEP X-RAY OBSERVATIONS OF THE YOUNG HIGH-MAGNETIC-FIELD RADIO PULSAR J1119–6127 AND SUPERNOVA REMNANT G292.2–0.5

International Nuclear Information System (INIS)

Ng, C.-Y.; Kaspi, V. M.; Ho, W. C. G.; Weltevrede, P.; Bogdanov, S.; Shannon, R.; Gonzalez, M. E.

2012-01-01

High-magnetic-field radio pulsars are important transition objects for understanding the connection between magnetars and conventional radio pulsars. We present a detailed study of the young radio pulsar J1119–6127, which has a characteristic age of 1900 yr and a spin-down-inferred magnetic field of 4.1 × 10 13 G, and its associated supernova remnant G292.2–0.5, using deep XMM-Newton and Chandra X-ray Observatory exposures of over 120 ks from each telescope. The pulsar emission shows strong modulation below 2.5 keV with a single-peaked profile and a large pulsed fraction of 0.48 ± 0.12. Employing a magnetic, partially ionized hydrogen atmosphere model, we find that the observed pulse profile can be produced by a single hot spot of temperature 0.13 keV covering about one-third of the stellar surface, and we place an upper limit of 0.08 keV for an antipodal hot spot with the same area. The non-uniform surface temperature distribution could be the result of anisotropic heat conduction under a strong magnetic field, and a single-peaked profile seems common among high-B radio pulsars. For the associated remnant G292.2–0.5, its large diameter could be attributed to fast expansion in a low-density wind cavity, likely formed by a Wolf-Rayet progenitor, similar to two other high-B radio pulsars.

FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE VELA-X PULSAR WIND NEBULA

International Nuclear Information System (INIS)

Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Borgland, A. W.; Bouvier, A.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bonamente, E.; Brigida, M.; Bruel, P.

2010-01-01

We report on gamma-ray observations in the off-pulse window of the Vela pulsar PSR B0833-45 using 11 months of survey data from the Fermi Large Area Telescope (LAT). This pulsar is located in the 8 deg. diameter Vela supernova remnant, which contains several regions of non-thermal emission detected in the radio, X-ray, and gamma-ray bands. The gamma-ray emission detected by the LAT lies within one of these regions, the 2 deg. x 3 deg. area south of the pulsar known as Vela-X. The LAT flux is significantly spatially extended with a best-fit radius of 0. 0 88 ± 0. 0 12 for an assumed radially symmetric uniform disk. The 200 MeV to 20 GeV LAT spectrum of this source is well described by a power law with a spectral index of 2.41 ± 0.09 ± 0.15 and integral flux above 100 MeV of (4.73 ± 0.63 ± 1.32) x 10 -7 cm -2 s -1 . The first errors represent the statistical error on the fit parameters, while the second ones are the systematic uncertainties. Detailed morphological and spectral analyses give strong constraints on the energetics and magnetic field of the pulsar wind nebula system and favor a scenario with two distinct electron populations.

Discovery of a cyclotron absorption line in the spectrum of the binary X-ray pulsar 4U 1538 - 52 observed by Ginga

Science.gov (United States)

Clark, George W.; Woo, Jonathan W.; Nagase, Fumiaki; Makishima, Kazuo; Sakao, Taro

1990-01-01

A cyclotron absorption line near 20 keV has been found in the spectrum of the massive eclipsing binary X-ray pulsar 4U 1538 - 52 in observations with the Ginga observatory. The line is detected throughout the 529 s pulse cycle with a variable equivalent width that has its maximum value during the smaller peak of the two-peak pulse profile. It is found that the profile of the pulse and the phase-dependence of the cyclotron line can be explained qualitatively by a pulsar model based on recent theoretical results on the properties of pencil beams emitted by accretion-heated slabs of magnetized plasma at the magnetic poles of a neutron star. The indicated field at the surface of the neutron star is 1.7 (1 + z) x 10 to the 12th G, where z is the gravitational redshift.

Radio spectra of pulsars. Pt. 1

International Nuclear Information System (INIS)

Izekova, V.A.; Kuzmin, A.D.; Malofeev, V.M.; Shitov, Yu.P.

1981-01-01

The results of flux pulsar radioemission measurements at meter wavelength, made at Pushchino Radio Astronomical Observatory of the Lebedev Physical Institute, are presented. Flux densities at 102, 85, 61 and 39 MHz have been measured for 85, 29, 37 and 23 pulsars correspondingly. Some of them were performed at all frequencies simultaneously. On the basis of these data and high frequencies data obtained by other authors, spectra of 52 pulsars were plotted. In practically all investigated pulsars we have detected a turn-over frequency at which the flux density of pulsar radioemission attained its maximum. Its mean value is vsub(m) = 130 +- 80 MHz. Averaged on many pulsars, the spectral index is negative in the 39-61 MHz frequency range (anti ALPHA 39 sub(-) 61 = -1.4 +- 0.4) and passes through zero at frequencies of about 100 MHz, becoming positive in the 100-400 MHz frequency range. It was noticed that the spectral index in the 100-400 MHz interval depends upon such pulsar periods as α 100 sub(-) 400 = 0.7 log p + 0.9. Using the spectra, more precise radio luminosities of pulsars have been computed. (orig.)

Radio emissions from pulsar companions: a refutable explanation for galactic transients and fast radio bursts

Science.gov (United States)

Mottez, F.; Zarka, P.

2014-09-01

Context. The six known highly dispersed fast radio bursts are attributed to extragalactic radio sources that are of unknown origin but extremely energetic. We propose here a new explanation that does not require an extreme release of energy and involves a body (planet, asteroid, white dwarf) orbiting an extragalactic pulsar. Aims: We investigate a theory of radio waves associated with such pulsar-orbiting bodies. We focus our analysis on the waves emitted from the magnetic wake of the body in the pulsar wind. After deriving their properties, we compare them with the observations of various transient radio signals to determine whether they could originate from pulsar-orbiting bodies. Methods: The analysis is based on the theory of Alfvén wings: for a body immersed in a pulsar wind, a system of two stationary Alfvén waves is attached to the body, provided that the wind is highly magnetised. When they are destabilised through plasma instabilities, Alfvén wings can be the locus of strong radio sources that are convected with the pulsar wind. By assuming a cyclotron maser instability operating in the Alfvén wings, we make predictions about the shape, frequencies, and brightness of the resulting radio emissions. Results: Because of the beaming by relativistic aberration, the signal is seen only when the companion is perfectly aligned between its parent pulsar and the observer, as is the case for occultations. For pulsar winds with a high Lorentz factor (≥104), the whole duration of the radio event does not exceed a few seconds, and it is composed of one to four peaks that last a few milliseconds each and are detectable up to distances of several Mpc. The Lorimer burst, the three isolated pulses of PSR J1928+15, and the recently detected fast radio bursts are all compatible with our model. According to it, these transient signals should repeat periodically with the companion's orbital period. Conclusions: The search of pulsar-orbiting bodies could be an exploration

Real-Time RFI Mitigation in Pulsar Observations

Science.gov (United States)

Ramey, Emily; Joslyn, Nick; Prestage, Richard; Whitehead, Mark; Lam, Michael Timothy; Blattner, Tim; Hawkins, Luke; Viou, Cedric; Masson, Jessica

2018-01-01

As the use of wireless technology has increased around the world, Radio Frequency Interference (RFI) has become more and more of a problem for radio astronomers. Preventative measures exist to limit the presence of RFI, and programs exist to remove it from saved data, but the routine use of algorithms to detect and remove RFI as an observation is occurring is much less common. Such a method would be incredibly useful for observations in which the data must undergo several rounds of processing before being saved, as in pulsar timing studies. Strategies for real-time mitigation have been discussed and tested with simulated data (Buch et al., 2016), but ideally the results of any approach would be validated by a detailed comparison of the final data products - for pulsar timing, the variance in the pulse times of arrival (TOAs) - with and without mitigation applied. The goal of this project is to develop an RFI mitigation approach based on the previously suggested strategies and test this program on actual data from the observation of pulsar J1713+0747. We use a Median Absolute Deviation (MAD) filter to identify interference in the observation and replace the compromised data with random Gaussian noise to match a characteristic radio signal from space. In order to verify our results, we analyze the pulsar’s TOAs obtained both from the mitigated data and from the unmitigated data processed through offline RFI removal software. Comparing the two, our preliminary findings indicate that our program is able to improve the quality of timing results from the observation.

Rotation and Accretion Powered Pulsars

Energy Technology Data Exchange (ETDEWEB)

Kaspi, V M [Department of Physics, McGill University, 3600 University St, Montreal, QC H3A 2T8 (Canada)

2008-03-07

Pulsar astrophysics has come a long way in the 40 years since the discovery of the first pulsar by Bell and Hewish. From humble beginnings as bits of 'scruff' on the Cambridge University group's chart recorder paper, the field of pulsars has blossomed into a major area of mainstream astrophysics, with an unparalleled diversity of astrophysical applications. These range from Nobel-celebrated testing of general relativity in the strong-field regime to constraining the equation-of-state of ultradense matter; from probing the winds of massive stars to globular cluster evolution. Previous notable books on the subject of pulsars have tended to focus on some particular topic in the field. The classic text Pulsars by Manchester and Taylor (1977 San Francisco, CA: Freeman) targeted almost exclusively rotation-powered radio pulsars, while the Meszaros book High-Energy Radiation from Magnetized Neutron Stars (1992 Chicago, IL: University of Chicago Press) considered both rotation- and accretion-powered neutron stars, but focused on their radiation at x-ray energies and above. The recent book Neutron Stars 1 by Haensel et al (2007 Berlin: Springer) considers only the equation of state and neutron-star structure. Into this context appears Rotation and Accretion Powered Pulsars, by Pranab Ghosh. In contrast to other books, here the author takes an encyclopedic approach and attempts to synthesize practically all of the major aspects of the two main types of neutron star. This is ambitious. The only comparable undertaking is the useful but more elementary Lyne and Graham-Smith text Pulsar Astronomy (1998 Cambridge: Cambridge University Press), or Compact Stellar X-ray Sources (eds Lewin and van der Klis, 2006 Cambridge: Cambridge University Press), an anthology of technical review articles that also includes black hole topics. Rotation and Accretion Powered Pulsars thus fills a clear void in the field, providing a readable, graduate-level book that covers nearly

Rotation and Accretion Powered Pulsars

International Nuclear Information System (INIS)

Kaspi, V M

2008-01-01

Pulsar astrophysics has come a long way in the 40 years since the discovery of the first pulsar by Bell and Hewish. From humble beginnings as bits of 'scruff' on the Cambridge University group's chart recorder paper, the field of pulsars has blossomed into a major area of mainstream astrophysics, with an unparalleled diversity of astrophysical applications. These range from Nobel-celebrated testing of general relativity in the strong-field regime to constraining the equation-of-state of ultradense matter; from probing the winds of massive stars to globular cluster evolution. Previous notable books on the subject of pulsars have tended to focus on some particular topic in the field. The classic text Pulsars by Manchester and Taylor (1977 San Francisco, CA: Freeman) targeted almost exclusively rotation-powered radio pulsars, while the Meszaros book High-Energy Radiation from Magnetized Neutron Stars (1992 Chicago, IL: University of Chicago Press) considered both rotation- and accretion-powered neutron stars, but focused on their radiation at x-ray energies and above. The recent book Neutron Stars 1 by Haensel et al (2007 Berlin: Springer) considers only the equation of state and neutron-star structure. Into this context appears Rotation and Accretion Powered Pulsars, by Pranab Ghosh. In contrast to other books, here the author takes an encyclopedic approach and attempts to synthesize practically all of the major aspects of the two main types of neutron star. This is ambitious. The only comparable undertaking is the useful but more elementary Lyne and Graham-Smith text Pulsar Astronomy (1998 Cambridge: Cambridge University Press), or Compact Stellar X-ray Sources (eds Lewin and van der Klis, 2006 Cambridge: Cambridge University Press), an anthology of technical review articles that also includes black hole topics. Rotation and Accretion Powered Pulsars thus fills a clear void in the field, providing a readable, graduate-level book that covers nearly everything you

Magnetic field shielding system in a tokamak experimental power reactor (EPR): concept and calculations

International Nuclear Information System (INIS)

Peng, Y.K.M.; Marcus, F.B.; Dory, R.A.; Moore, J.R.

1975-01-01

A poloidal magnetic field shielding system is proposed for a tokamak EPR. This coil system minimizes the pulsed poloidal field that intersects the TF (toroidal field) coils and hence reduces the risk of superconductor quenching and structural failure of the coils. Based on an idealized shielding model, we have determined the configurations for the OH (ohmic heating), the S-VF (shield-vertical field), and the T-VF (trimming-vertical field) coils in a typical tokamak EPR. It is found that the pulsed poloidal field strength is greatly reduced in the TF coil region. The overall requirement in stored plasma and vertical field energy is also substantially reduced when compared with conventional EPR designs. Use of this field shielding system is expected to enhance reliability of the superconducting TF coils in a tokamak EPR

MEASURING THE MASS OF SOLAR SYSTEM PLANETS USING PULSAR TIMING

International Nuclear Information System (INIS)

Champion, D. J.; Hobbs, G. B.; Manchester, R. N.; Edwards, R. T.; Burke-Spolaor, S.; Sarkissian, J. M.; Backer, D. C.; Bailes, M.; Bhat, N. D. R.; Van Straten, W.; Coles, W.; Demorest, P. B.; Ferdman, R. D.; Purver, M. B.; Folkner, W. M.; Hotan, A. W.; Kramer, M.; Lommen, A. N.; Nice, D. J.; Stairs, I. H.

2010-01-01

High-precision pulsar timing relies on a solar system ephemeris in order to convert times of arrival (TOAs) of pulses measured at an observatory to the solar system barycenter. Any error in the conversion to the barycentric TOAs leads to a systematic variation in the observed timing residuals; specifically, an incorrect planetary mass leads to a predominantly sinusoidal variation having a period and phase associated with the planet's orbital motion about the Sun. By using an array of pulsars (PSRs J0437-4715, J1744-1134, J1857+0943, J1909-3744), the masses of the planetary systems from Mercury to Saturn have been determined. These masses are consistent with the best-known masses determined by spacecraft observations, with the mass of the Jovian system, 9.547921(2) x10 -4 M sun , being significantly more accurate than the mass determined from the Pioneer and Voyager spacecraft, and consistent with but less accurate than the value from the Galileo spacecraft. While spacecraft are likely to produce the most accurate measurements for individual solar system bodies, the pulsar technique is sensitive to planetary system masses and has the potential to provide the most accurate values of these masses for some planets.

Astronomers Discover Fastest-Spinning Pulsar

Science.gov (United States)

2006-01-01

Astronomers using the National Science Foundation's Robert C. Byrd Green Bank Telescope have discovered the fastest-spinning neutron star ever found, a 20-mile-diameter superdense pulsar whirling faster than the blades of a kitchen blender. Their work yields important new information about the nature of one of the most exotic forms of matter known in the Universe. Pulsar Graphic Pulsars Are Spinning Neutron Stars CREDIT: Bill Saxton, NRAO/AUI/NSF (Click on image for larger version) "We believe that the matter in neutron stars is denser than an atomic nucleus, but it is unclear by how much. Our observations of such a rapidly rotating star set a hard upper limit on its size, and hence on how dense the star can be.," said Jason Hessels, a graduate student at McGill University in Montreal. Hessels and his colleagues presented their findings to the American Astronomical Society's meeting in Washington, DC. Pulsars are spinning neutron stars that sling "lighthouse beams" of radio waves or light around as they spin. A neutron star is what is left after a massive star explodes at the end of its "normal" life. With no nuclear fuel left to produce energy to offset the stellar remnant's weight, its material is compressed to extreme densities. The pressure squeezes together most of its protons and electrons to form neutrons; hence, the name "neutron star." "Neutron stars are incredible laboratories for learning about the physics of the fundamental particles of nature, and this pulsar has given us an important new limit," explained Scott Ransom, an astronomer at the National Radio Astronomy Observatory and one of Hessels' collaborators on this work. The scientists discovered the pulsar, named PSR J1748-2446ad, in a globular cluster of stars called Terzan 5, located some 28,000 light-years from Earth in the constellation Sagittarius. The newly-discovered pulsar is spinning 716 times per second, or at 716 Hertz (Hz), readily beating the previous record of 642 Hz from a pulsar

Galactic distribution and evolution of pulsars

International Nuclear Information System (INIS)

Taylor, J.H.; Manchester, R.N.

1977-01-01

The distribution of pulsars with respect to period, z-distance, luminosity, and galactocentric radius has been investigated using data from three extensive pulsar surveys. It is shown that selection effects only slightly modify the observed period and z-distributions but strongly affect the observed luminosity function and galactic distribution. These latter two distributions are computed from the Jodrell Bank and Arecibo data, using an iterative procedure. The largest uncertainties in our results are the result of uncertainty in the adopted distance scale. Therefore, where relevant, separate calculations have been made for two values of the average interstellar electron density, , 0.02 cm -3 and 0.03 cm -3 .The derived luminosity function is closely represented by a power law with index (for logarithmic luminosity intervals) close to -1. For =0.03 cm -3 , the density of potentially observable pulsars is about 90 kpc -2 in the local region and increases with decreasing galactocentric radius. These distributions imply that the total number of pulsars in the Galaxy is about 10 5 . If only a fraction of all pulsars are observable because of beaming effects, then the total number in the Galaxy is correspondingly greater.Recent observations of pulsar proper motions show that pulsars are generally high-velocity objects. The observed z-distribution of pulsars implies that the mean age of observable pulsars does not exceed 2 x 10 6 years. With this mean age the pulsar birthrate required to maintain the observed galactic distribution is 10 -4 yr -1 kpc -2 in the local region and one pulsar birth every 6 years in the Galaxy as a whole. For =0.02 cm -3 , the corresponding rate is one birth every 40 years. These rates exceed most estimates of supernova occurrence rates and may require that all stars with mass greater than approx.2.5 Msun form pulsars at the end of their evolutionary life

Runaway electrons in the TRIAM-1 tokamak

International Nuclear Information System (INIS)

Satoh, Takemichi; Nakamura, Kazuo; Toi, Kazuo; Nakamura, Yukio; Hiraki, Naoji

1981-01-01

Pulse height analysis of soft X-rays is carried out in the TRIAM-1 tokamak. The electron temperatures determined from the soft X-ray spectrum agree well with those from Thomson scattering. It is observed that low-energy runaway (slideaway) electrons appear in the high-current-density discharges. (author)

Runaway electrons in the TRIAM-1 tokamak

Energy Technology Data Exchange (ETDEWEB)

Satoh, T; Nakamura, K; Toi, K; Nakamura, Y; Hiraki, N [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics

1981-09-01

Pulse height analysis of soft X-rays is carried out in the TRIAM-1 tokamak. The electron temperatures determined from the soft X-ray spectrum agree well with those from Thomson scattering. It is observed that low-energy runaway (slideaway) electrons appear in the high-current-density discharges.

LIDAR Thomson scattering for advanced tokamaks. Final report

International Nuclear Information System (INIS)

Molvik, A.W.; Lerche, R.A.; Nilson, D.G.

1996-01-01

The LIDAR Thomson Scattering for Advanced Tokamaks project made a valuable contribution by combining LLNL expertise from the MFE Program: tokamak design and diagnostics, and the ICF Program and Physics Dept.: short-pulse lasers and fast streak cameras. This multidisciplinary group evaluated issues involved in achieving a factor of 20 higher high spatial resolution (to as small as 2-3 mm) from the present state of the art in LIDAR Thomson scattering, and developed conceptual designs to apply LIDAR Thomson scattering to three tokamaks: Upgraded divertor measurements in the existing DIII-D tokamak; Both core and divertor LIDAR Thomson scattering in the proposed (now cancelled) TPX; and core, edge, and divertor LIDAR Thomson scattering on the presently planned International Tokamak Experimental Reactor, ITER. Other issues were evaluated in addition to the time response required for a few millimeter spatial resolution. These include the optimum wavelength, 100 Hz operation of the laser and detectors, minimizing stray light - always the Achilles heel of Thomson scattering, and time dispersion in optics that could prevent good spatial resolution. Innovative features of our work included: custom short pulsed laser concepts to meet specific requirements, use of a prism spectrometer to maintain a constant optical path length for high temporal and spatial resolution, the concept of a laser focus outside the plasma to ionize gas and form an external fiducial to use in locating the plasma edge as well as to spread the laser energy over a large enough area of the inner wall to avoid laser ablation of wall material, an improved concept for cleaning windows between shots by means of laser ablation, and the identification of a new physics issue - nonlinear effects near a laser focus which could perturb the plasma density and temperature that are to be measured

Pulsar-irradiated stars in dense globular clusters

Science.gov (United States)

Tavani, Marco

1992-01-01

We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

Design of a microwave calorimeter for the microwave tokamak experiment

International Nuclear Information System (INIS)

Marinak, M.

1988-01-01

The initial design of a microwave calorimeter for the Microwave Tokamak Experiment is presented. The design is optimized to measure the refraction and absorption of millimeter rf microwaves as they traverse the toroidal plasma of the Alcator C tokamak. Techniques utilized can be adapted for use in measuring high intensity pulsed output from a microwave device in an environment of ultra high vacuum, intense fields of ionizing and non-ionizing radiation and intense magnetic fields. 16 refs

SIGPROC: Pulsar Signal Processing Programs

Science.gov (United States)

Lorimer, D. R.

2011-07-01

SIGPROC is a package designed to standardize the initial analysis of the many types of fast-sampled pulsar data. Currently recognized machines are the Wide Band Arecibo Pulsar Processor (WAPP), the Penn State Pulsar Machine (PSPM), the Arecibo Observatory Fourier Transform Machine (AOFTM), the Berkeley Pulsar Processors (BPP), the Parkes/Jodrell 1-bit filterbanks (SCAMP) and the filterbank at the Ooty radio telescope (OOTY). The SIGPROC tools should help users look at their data quickly, without the need to write (yet) another routine to read data or worry about big/little endian compatibility (byte swapping is handled automatically).

Free-electron laser experiments in the microwave tokamak experiment

International Nuclear Information System (INIS)

Allen, S.L.; Brown, M.D.; Byers, J.A.; Casper, T.A.; Cohen, B.I.; Cohen, R.H.; Cummings, J.C.; Fenstermacher, M.E.; Foote, J.H.; Hooper, E.B.; Jong, R.A.; Langdon, A.B.; Lasinski, B.F.; Lasnier, C.J.; Matsuda, Y.; Meyer, W.H.; Moller, J.M.; Nexsen, W.E.; Rice, B.W.; Rognlien, T.D.; Smith, G.R.; Stallard, B.W.; Thomassen, K.I.; Throop, A.L.; Turner, W.C.; Wood, R.D.; Cook, D.R.; Makowski, M.A.; Oasa, K.; Ogawa, T.

1990-08-01

Microwave pulses have been injected from a free electron-laser (FEL) into the Microwave Tokamak Experiment (MTX) at up to 0.2 GW at 140 GHz in short pulses (10-ns duration) with O-mode polarization. The power transmitted through the plasma was measured in a first experimental study of high power pulse propagation in the plasma; no nonlinear effects were found at this power level. Calculations indicate that nonlinear effects may be found at the higher power densities expected in future experiments. 9 refs., 2 figs

Pulsar Timing with the Fermi LAT

Science.gov (United States)

2010-12-01

Pulsar Timing with the Fermi LAT Paul S. Ray∗, Matthew Kerr†, Damien Parent∗∗ and the Fermi PSC‡ ∗Naval Research Laboratory, 4555 Overlook Ave., SW...Laboratory, Washington, DC 20375, USA ‡Fermi Pulsar Search Consortium Abstract. We present an overview of precise pulsar timing using data from the Large...unbinned photon data. In addition to determining the spindown behavior of the pulsars and detecting glitches and timing noise, such timing analyses al

Microwave measurements of the time evolution of electron density in the T-11M tokamak

International Nuclear Information System (INIS)

Petrov, V.G.; Petrov, A.A.; Malyshev, A.Yu.; Markov, V.K.; Babarykin, A.V.

2004-01-01

Unambiguous diagnostics intended for measuring the time behavior of the electron density and monitoring the line-averaged plasma density in the T-11M tokamak are described. The time behavior of the plasma density in the T-11M tokamak is measured by a multichannel phase-jump-free microwave polarization interferometer based on the Cotton-Mouton effect. After increasing the number of simultaneously operating interferometer channels and enhancing the sensitivity of measurements, it became possible to measure the time evolution of the plasma density profile in the T-11M tokamak. The first results from such measurements in various operating regimes of the T-11M tokamak are presented. The measurement and data processing techniques are described, the measurement errors are analyzed, and the results obtained are discussed. We propose using a pulsed time-of-flight refractometer to monitor the average plasma density in the T-11M tokamak. The refractometer emits nanosecond microwave probing pulses with a carrier frequency that is higher than the plasma frequency and, thus, operates in the transmission mode. A version of the instrument has been developed with a carrier frequency of 140 GHz, which allows one to measure the average density in regimes with a nominal T-11M plasma density of (3-5) x 10 13 cm -3 . Results are presented from the first measurements of the average density in the T-11M tokamak with the help of a pulsed time-of-flight refractometer by probing the plasma in the equatorial plane in a regime with the reflection of the probing radiation from the inner wall of the vacuum chamber

Heat pulse propagation studies in TFTR

Energy Technology Data Exchange (ETDEWEB)

Fredrickson, E.D.; Callen, J.D.; Colchin, R.J.; Efthimion, P.C.; Hill, K.W.; Izzo, R.; Mikkelsen, D.R.; Monticello, D.A.; McGuire, K.; Bell, J.D.

1986-02-01

The time scales for sawtooth repetition and heat pulse propagation are much longer (10's of msec) in the large tokamak TFTR than in previous, smaller tokamaks. This extended time scale coupled with more detailed diagnostics has led us to revisit the analysis of the heat pulse propagation as a method to determine the electron heat diffusivity, chi/sub e/, in the plasma. A combination of analytic and computer solutions of the electron heat diffusion equation are used to clarify previous work and develop new methods for determining chi/sub e/. Direct comparison of the predicted heat pulses with soft x-ray and ECE data indicates that the space-time evolution is diffusive. However, the chi/sub e/ determined from heat pulse propagation usually exceeds that determined from background plasma power balance considerations by a factor ranging from 2 to 10. Some hypotheses for resolving this discrepancy are discussed. 11 refs., 19 figs., 1 tab.

Heat pulse propagation studies in TFTR

International Nuclear Information System (INIS)

Fredrickson, E.D.; Callen, J.D.; Colchin, R.J.

1986-02-01

The time scales for sawtooth repetition and heat pulse propagation are much longer (10's of msec) in the large tokamak TFTR than in previous, smaller tokamaks. This extended time scale coupled with more detailed diagnostics has led us to revisit the analysis of the heat pulse propagation as a method to determine the electron heat diffusivity, chi/sub e/, in the plasma. A combination of analytic and computer solutions of the electron heat diffusion equation are used to clarify previous work and develop new methods for determining chi/sub e/. Direct comparison of the predicted heat pulses with soft x-ray and ECE data indicates that the space-time evolution is diffusive. However, the chi/sub e/ determined from heat pulse propagation usually exceeds that determined from background plasma power balance considerations by a factor ranging from 2 to 10. Some hypotheses for resolving this discrepancy are discussed. 11 refs., 19 figs., 1 tab

Magnetic absorption of VHE photons in the magnetosphere of the Crab pulsar

Science.gov (United States)

Bogovalov, S. V.; Contopoulos, I.; Prosekin, A.; Tronin, I.; Aharonian, F. A.

2018-05-01

The detection of the pulsed ˜1 TeV gamma-ray emission from the Crab pulsar reported by MAGIC and VERITAS collaborations demands a substantial revision of existing models of particle acceleration in the pulsar magnetosphere. In this regard model independent restrictions on the possible production site of the very high energy (VHE) photons become an important issue. In this paper, we consider limitations imposed by the process of conversion of VHE gamma-rays into e± pairs in the magnetic field of the pulsar magnetosphere. Photons with energies exceeding 1 TeV are effectively absorbed even at large distances from the surface of the neutron star. Our calculations of magnetic absorption in the force-free magnetosphere show that the twisting of the magnetic field due to the pulsar rotation makes the magnetosphere more transparent compared to the dipole magnetosphere. The gamma-ray absorption appears stronger for photons emitted in the direction of rotation than in the opposite direction. There is a small angular cone inside which the magnetosphere is relatively transparent and photons with energy 1.5 TeV can escape from distances beyond 0.1 light cylinder radius (Rlc). The emission surface from where photons can be emitted in the observer's direction further restricts the sites of VHE gamma-ray production. For the observation angle 57° relative to the Crab pulsar axis of rotation and the orthogonal rotation, the emission surface in the open field line region is located as close as 0.4 Rlc from the stellar surface for a dipole magnetic field, and 0.1 Rlc for a force-free magnetic field.

Searching for pulsars using image pattern recognition

Energy Technology Data Exchange (ETDEWEB)

Zhu, W. W.; Berndsen, A.; Madsen, E. C.; Tan, M.; Stairs, I. H. [Department of Physics and Astronomy, 6224 Agricultural Road, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Brazier, A. [Astronomy Department, Cornell University, Ithaca, NY 14853 (United States); Lazarus, P. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Lynch, R.; Scholz, P. [Department of Physics, McGill University, Montreal, QC H3A 2T8 (Canada); Stovall, K.; Cohen, S.; Dartez, L. P.; Lunsford, G.; Martinez, J. G.; Mata, A. [Center for Advanced Radio Astronomy, University of Texas at Brownsville, Brownsville, TX 78520 (United States); Ransom, S. M. [NRAO, Charlottesville, VA 22903 (United States); Banaszak, S.; Biwer, C. M.; Flanigan, J.; Rohr, M., E-mail: zhuww@phas.ubc.ca, E-mail: berndsen@phas.ubc.ca [Center for Gravitation, Cosmology and Astrophysics. University of Wisconsin Milwaukee, Milwaukee, WI 53211 (United States); and others

2014-02-01

In the modern era of big data, many fields of astronomy are generating huge volumes of data, the analysis of which can sometimes be the limiting factor in research. Fortunately, computer scientists have developed powerful data-mining techniques that can be applied to various fields. In this paper, we present a novel artificial intelligence (AI) program that identifies pulsars from recent surveys by using image pattern recognition with deep neural nets—the PICS (Pulsar Image-based Classification System) AI. The AI mimics human experts and distinguishes pulsars from noise and interference by looking for patterns from candidate plots. Different from other pulsar selection programs that search for expected patterns, the PICS AI is taught the salient features of different pulsars from a set of human-labeled candidates through machine learning. The training candidates are collected from the Pulsar Arecibo L-band Feed Array (PALFA) survey. The information from each pulsar candidate is synthesized in four diagnostic plots, which consist of image data with up to thousands of pixels. The AI takes these data from each candidate as its input and uses thousands of such candidates to train its ∼9000 neurons. The deep neural networks in this AI system grant it superior ability to recognize various types of pulsars as well as their harmonic signals. The trained AI's performance has been validated with a large set of candidates from a different pulsar survey, the Green Bank North Celestial Cap survey. In this completely independent test, the PICS ranked 264 out of 277 pulsar-related candidates, including all 56 previously known pulsars and 208 of their harmonics, in the top 961 (1%) of 90,008 test candidates, missing only 13 harmonics. The first non-pulsar candidate appears at rank 187, following 45 pulsars and 141 harmonics. In other words, 100% of the pulsars were ranked in the top 1% of all candidates, while 80% were ranked higher than any noise or interference. The

Searching for pulsars using image pattern recognition

International Nuclear Information System (INIS)

Zhu, W. W.; Berndsen, A.; Madsen, E. C.; Tan, M.; Stairs, I. H.; Brazier, A.; Lazarus, P.; Lynch, R.; Scholz, P.; Stovall, K.; Cohen, S.; Dartez, L. P.; Lunsford, G.; Martinez, J. G.; Mata, A.; Ransom, S. M.; Banaszak, S.; Biwer, C. M.; Flanigan, J.; Rohr, M.

2014-01-01

In the modern era of big data, many fields of astronomy are generating huge volumes of data, the analysis of which can sometimes be the limiting factor in research. Fortunately, computer scientists have developed powerful data-mining techniques that can be applied to various fields. In this paper, we present a novel artificial intelligence (AI) program that identifies pulsars from recent surveys by using image pattern recognition with deep neural nets—the PICS (Pulsar Image-based Classification System) AI. The AI mimics human experts and distinguishes pulsars from noise and interference by looking for patterns from candidate plots. Different from other pulsar selection programs that search for expected patterns, the PICS AI is taught the salient features of different pulsars from a set of human-labeled candidates through machine learning. The training candidates are collected from the Pulsar Arecibo L-band Feed Array (PALFA) survey. The information from each pulsar candidate is synthesized in four diagnostic plots, which consist of image data with up to thousands of pixels. The AI takes these data from each candidate as its input and uses thousands of such candidates to train its ∼9000 neurons. The deep neural networks in this AI system grant it superior ability to recognize various types of pulsars as well as their harmonic signals. The trained AI's performance has been validated with a large set of candidates from a different pulsar survey, the Green Bank North Celestial Cap survey. In this completely independent test, the PICS ranked 264 out of 277 pulsar-related candidates, including all 56 previously known pulsars and 208 of their harmonics, in the top 961 (1%) of 90,008 test candidates, missing only 13 harmonics. The first non-pulsar candidate appears at rank 187, following 45 pulsars and 141 harmonics. In other words, 100% of the pulsars were ranked in the top 1% of all candidates, while 80% were ranked higher than any noise or interference. The

Searching for Pulsars Using Image Pattern Recognition

Science.gov (United States)

Zhu, W. W.; Berndsen, A.; Madsen, E. C.; Tan, M.; Stairs, I. H.; Brazier, A.; Lazarus, P.; Lynch, R.; Scholz, P.; Stovall, K.; Ransom, S. M.; Banaszak, S.; Biwer, C. M.; Cohen, S.; Dartez, L. P.; Flanigan, J.; Lunsford, G.; Martinez, J. G.; Mata, A.; Rohr, M.; Walker, A.; Allen, B.; Bhat, N. D. R.; Bogdanov, S.; Camilo, F.; Chatterjee, S.; Cordes, J. M.; Crawford, F.; Deneva, J. S.; Desvignes, G.; Ferdman, R. D.; Freire, P. C. C.; Hessels, J. W. T.; Jenet, F. A.; Kaplan, D. L.; Kaspi, V. M.; Knispel, B.; Lee, K. J.; van Leeuwen, J.; Lyne, A. G.; McLaughlin, M. A.; Siemens, X.; Spitler, L. G.; Venkataraman, A.

2014-02-01

In the modern era of big data, many fields of astronomy are generating huge volumes of data, the analysis of which can sometimes be the limiting factor in research. Fortunately, computer scientists have developed powerful data-mining techniques that can be applied to various fields. In this paper, we present a novel artificial intelligence (AI) program that identifies pulsars from recent surveys by using image pattern recognition with deep neural nets—the PICS (Pulsar Image-based Classification System) AI. The AI mimics human experts and distinguishes pulsars from noise and interference by looking for patterns from candidate plots. Different from other pulsar selection programs that search for expected patterns, the PICS AI is taught the salient features of different pulsars from a set of human-labeled candidates through machine learning. The training candidates are collected from the Pulsar Arecibo L-band Feed Array (PALFA) survey. The information from each pulsar candidate is synthesized in four diagnostic plots, which consist of image data with up to thousands of pixels. The AI takes these data from each candidate as its input and uses thousands of such candidates to train its ~9000 neurons. The deep neural networks in this AI system grant it superior ability to recognize various types of pulsars as well as their harmonic signals. The trained AI's performance has been validated with a large set of candidates from a different pulsar survey, the Green Bank North Celestial Cap survey. In this completely independent test, the PICS ranked 264 out of 277 pulsar-related candidates, including all 56 previously known pulsars and 208 of their harmonics, in the top 961 (1%) of 90,008 test candidates, missing only 13 harmonics. The first non-pulsar candidate appears at rank 187, following 45 pulsars and 141 harmonics. In other words, 100% of the pulsars were ranked in the top 1% of all candidates, while 80% were ranked higher than any noise or interference. The

PEACE: pulsar evaluation algorithm for candidate extraction - a software package for post-analysis processing of pulsar survey candidates

Science.gov (United States)

Lee, K. J.; Stovall, K.; Jenet, F. A.; Martinez, J.; Dartez, L. P.; Mata, A.; Lunsford, G.; Cohen, S.; Biwer, C. M.; Rohr, M.; Flanigan, J.; Walker, A.; Banaszak, S.; Allen, B.; Barr, E. D.; Bhat, N. D. R.; Bogdanov, S.; Brazier, A.; Camilo, F.; Champion, D. J.; Chatterjee, S.; Cordes, J.; Crawford, F.; Deneva, J.; Desvignes, G.; Ferdman, R. D.; Freire, P.; Hessels, J. W. T.; Karuppusamy, R.; Kaspi, V. M.; Knispel, B.; Kramer, M.; Lazarus, P.; Lynch, R.; Lyne, A.; McLaughlin, M.; Ransom, S.; Scholz, P.; Siemens, X.; Spitler, L.; Stairs, I.; Tan, M.; van Leeuwen, J.; Zhu, W. W.

2013-07-01

Modern radio pulsar surveys produce a large volume of prospective candidates, the majority of which are polluted by human-created radio frequency interference or other forms of noise. Typically, large numbers of candidates need to be visually inspected in order to determine if they are real pulsars. This process can be labour intensive. In this paper, we introduce an algorithm called Pulsar Evaluation Algorithm for Candidate Extraction (PEACE) which improves the efficiency of identifying pulsar signals. The algorithm ranks the candidates based on a score function. Unlike popular machine-learning-based algorithms, no prior training data sets are required. This algorithm has been applied to data from several large-scale radio pulsar surveys. Using the human-based ranking results generated by students in the Arecibo Remote Command Center programme, the statistical performance of PEACE was evaluated. It was found that PEACE ranked 68 per cent of the student-identified pulsars within the top 0.17 per cent of sorted candidates, 95 per cent within the top 0.34 per cent and 100 per cent within the top 3.7 per cent. This clearly demonstrates that PEACE significantly increases the pulsar identification rate by a factor of about 50 to 1000. To date, PEACE has been directly responsible for the discovery of 47 new pulsars, 5 of which are millisecond pulsars that may be useful for pulsar timing based gravitational-wave detection projects.

Surface temperature measurement of plasma facing components in tokamaks

International Nuclear Information System (INIS)

Amiel, Stephane

2014-01-01

During this PhD, the challenges on the non-intrusive surface temperature measurements of metallic plasma facing components in tokamaks are reported. Indeed, a precise material emissivity value is needed for classical infrared methods and the environment contribution has to be known particularly for low emissivities materials. Although methods have been developed to overcome these issues, they have been implemented solely for dedicated experiments. In any case, none of these methods are suitable for surface temperature measurement in tokamaks.The active pyrometry introduced in this study allows surface temperature measurements independently of reflected flux and emissivities using pulsed and modulated photothermal effect. This method has been validated in laboratory on metallic materials with reflected fluxes for pulsed and modulated modes. This experimental validation is coupled with a surface temperature variation induced by photothermal effect and temporal signal evolvement modelling in order to optimize both the heating source characteristics and the data acquisition and treatment. The experimental results have been used to determine the application range in temperature and detection wavelengths. In this context, the design of an active pyrometry system on tokamak has been completed, based on a bicolor camera for a thermography application in metallic (or low emissivity) environment.The active pyrometry method introduced in this study is a complementary technique of classical infrared methods used for thermography in tokamak environment which allows performing local and 2D surface temperature measurements independently of reflected fluxes and emissivities. (author) [fr

Advanced commercial Tokamak optimization studies

International Nuclear Information System (INIS)

Whitley, R.H.; Berwald, D.H.; Gordon, J.D.

1985-01-01

Our recent studies have concentrated on developing optimal high beta (bean-shaped plasma) commercial tokamak configurations using TRW's Tokamak Reactor Systems Code (TRSC) with special emphasis on lower net electric power reactors that are more easily deployable. A wide range of issues were investigated in the search for the most economic configuration: fusion power, reactor size, wall load, magnet type, inboard blanket and shield thickness, plasma aspect ratio, and operational β value. The costs and configurations of both steady-state and pulsed reactors were also investigated. Optimal small and large reactor concepts were developed and compared by studying the cost of electricity from single units and from multiplexed units. Multiplexed units appear to have advantages because they share some plant equipment and have lower initial capital investment as compared to larger single units

A SEARCH FOR RAPIDLY SPINNING PULSARS AND FAST TRANSIENTS IN UNIDENTIFIED RADIO SOURCES WITH THE NRAO 43 METER TELESCOPE

Energy Technology Data Exchange (ETDEWEB)

Schmidt, Deborah; Crawford, Fronefield; Gilpin, Claire [Department of Physics and Astronomy, Franklin and Marshall College, P.O. Box 3003, Lancaster, PA 17604 (United States); Langston, Glen [National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944 (United States)

2013-04-15

We have searched 75 unidentified radio sources selected from the NRAO VLA Sky Survey catalog for the presence of rapidly spinning pulsars and short, dispersed radio bursts. The sources are radio bright, have no identifications or optical source coincidences, are more than 5% linearly polarized, and are spatially unresolved in the catalog. If these sources are fast-spinning pulsars (e.g., sub-millisecond pulsars), previous large-scale pulsar surveys may have missed detection due to instrumental and computational limitations, eclipsing effects, or diffractive scintillation. The discovery of a sub-millisecond pulsar would significantly constrain the neutron star equation of state and would have implications for models predicting a rapid slowdown of highly recycled X-ray pulsars to millisecond periods from, e.g., accretion disk decoupling. These same sources were previously searched unsuccessfully for pulsations at 610 MHz with the Lovell Telescope at Jodrell Bank. This new search was conducted at a different epoch with a new 800 MHz backend on the NRAO 43 m Telescope at a center frequency of 1200 MHz. Our search was sensitive to sub-millisecond pulsars in highly accelerated binary systems and to short transient pulses. No periodic or transient signals were detected from any of the target sources. We conclude that diffractive scintillation, dispersive smearing, and binary acceleration are unlikely to have prevented detection of the large majority of the sources if they are pulsars, though we cannot rule out eclipsing, nulling or intermittent emission, or radio interference as possible factors for some non-detections. Other (speculative) possibilities for what these sources might include radio-emitting magnetic cataclysmic variables or older pulsars with aligned magnetic and spin axes.

The Pulsar Luminosity Function

OpenAIRE

O. H. Guseinov; E. Yazgan; S. O. Tagieva

2003-01-01

Hemos construido y examinado la función de luminosidad para pulsares, usando una nueva lista la cual incluye datos de 1328 radio pulsares. En este trabajo, se construye por primera vez la función de luminosidad en 1400 MHz. También presentamos una función de luminosidad mejorada en 400 MHz. Se comparan las funciones de luminosidad en 400 y 1400 MHz. De igual manera se construyen las funciones de luminosidad excluyendo los pulsares binarios y los de campos magnéticos pequeños. S...

Automated processing of pulsar observations

Energy Technology Data Exchange (ETDEWEB)

Byzhlov, B.V.; Ivanova, V.V.; Izvekova, V.A.; Kuz' min, A.D.; Kuz' min, Yu.P.; Malofeev, V.M.; Popov, Yu.M.; Solomin, N.S.; Shabanova, T.V.; Shitov, Yu.P.

1977-01-01

Digital computer technology which processes observation results in a real time scale is used on meter-range radiotelescopes DKR-100 of the USSR Academy of Sciences Physics Institute and the BSA of the Physics Institute to study pulsars. A method which calls for the accumulation of impulses with preliminary compensation of pulsar dispersion in a broad band is used to increase sensitivity and resolution capability. Known pulsars are studied with the aid of a ''neuron'' type analyzer. A system for processing observations in an on-line set-up was created on the M-6000 computer for seeking unknown pulsars. 8 figures, 1 table, references.

Theoretical Study of Gamma-ray Pulsars

Directory of Open Access Journals (Sweden)

Kwong Sang Cheng

2016-06-01

Full Text Available We use the non-stationary three dimensional two-layer outer gap model to explain gamma-ray emissions from a pulsar magnetosphere. We found out that for some pulsars like the Geminga pulsar, it was hard to explain emissions above a level of around 1 GeV. We then developed the model into a non-stationary model. In this model we assigned a power-law distribution to one or more of the spectral parameters proposed in the previous model and calculated the weighted phaseaveraged spectrum. Though this model is suitable for some pulsars, it still cannot explain the high energy emission of the Geminga pulsar. An Inverse-Compton Scattering component between the primary particles and the radio photons in the outer magnetosphere was introduced into the model, and this component produced a sufficient number of GeV photons in the spectrum of the Geminga pulsar.

Polarimetric Evidence of the First White Dwarf Pulsar: The Binary System AR Scorpii

Directory of Open Access Journals (Sweden)

David A.H. Buckley

2018-01-01

Full Text Available The binary star AR Scorpii was recently discovered to exhibit high amplitude coherent variability across the electromagnetic spectrum (ultraviolet to radio at two closely spaced ∼2 min periods, attributed to the spin period of a white dwarf and the beat period. There is strong evidence (low X-ray luminosity, lack of flickering and absense of broad emission lines that AR Sco is a detached non-accreting system whose luminosity is dominated by the spin-down power of a white dwarf, due to magnetohydrodynamical (MHD interactions with its M5 companion. Optical polarimetry has revealed highly pulsed linear polarization on the same periods, reaching a maximum of 40%, consistent with a pulsar-like dipole, with the Stokes Q and U variations reminiscent of the Crab pulsar. These observations, coupled with the spectral energy distribution (SED which is dominated by non-thermal emission, characteristic of synchrotron emission, support the notion that a strongly magnetic (∼200 MG white dwarf is behaving like a pulsar, whose magnetic field interacts with the secondary star’s photosphere and magnetosphere. Radio synchrotron emission is produced from the pumping action of the white dwarf’s magnetic field on coronal loops from the M-star companion, while emission at high frequencies (UV/optical/X-ray comes from the particle wind, driven by large electric potential, again reminiscent of processes seen in neutron star pulsars.

The Discovery of the Most Accelerated Binary Pulsar

OpenAIRE

Cameron, A. D.; Champion, D. J.; Kramer, M.; Bailes, M.; Barr, E. D.; Bassa, C. G.; Bhandari, S.; Bhat, N. D. R.; Burgay, M.; Burke-Spolaor, S.; Eatough, R. P.; Flynn, C. M. L.; Freire, P. C. C.; Jameson, A.; Johnston, S.

2018-01-01

Pulsars in relativistic binary systems have emerged as fantastic natural laboratories for testing theories of gravity, the most prominent example being the double pulsar, PSR J0737$-$3039. The HTRU-South Low Latitude pulsar survey represents one of the most sensitive blind pulsar surveys taken of the southern Galactic plane to date, and its primary aim has been the discovery of new relativistic binary pulsars. Here we present our binary pulsar searching strategy and report on the survey's fla...

A BROADBAND RADIO STUDY OF THE AVERAGE PROFILE AND GIANT PULSES FROM PSR B1821-24A

Energy Technology Data Exchange (ETDEWEB)

Bilous, A. V. [Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen (Netherlands); Pennucci, T. T. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States); Demorest, P. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); Ransom, S. M., E-mail: a.bilous@science.ru.nl [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)

2015-04-20

We present the results of a wideband (720–2400 MHz) study of PSR B1821–24A (J1824–2452A, M28A), an energetic millisecond pulsar (MSP) visible in radio, X-rays and γ-rays. In radio, the pulsar has a complex average profile that spans ≳85% of the spin period and exhibits strong evolution with observing frequency. For the first time we measure phase-resolved polarization properties and spectral indices of radio emission throughout almost all of the on-pulse window. We synthesize our findings with high-energy information to compare M28A to other known γ-ray MSPs and to speculate that M28A’s radio emission originates in multiple regions within its magnetosphere (i.e., both in the slot or outer gaps near the light cylinder and at lower altitudes above the polar cap). M28A is one of a handful of pulsars that are known to emit giant radio pulses (GRPs)—short, bright radio pulses of unknown nature. We report a drop in the linear polarization of the average profile in both windows of GRP generation and also a “W”-shaped absorption feature (resembling a double notch), partly overlapping with one of the GRP windows. The GRPs themselves have broadband spectra consisting of multiple patches with Δν/ν ∼ 0.07. Although our time resolution was not sufficient to resolve the GRP structure on the μs scale, we argue that GRPs from this pulsar most closely resemble the GRPs from the main pulse of the Crab pulsar, which consist of a series of narrowband nanoshots.

EXCESS OPTICAL ENHANCEMENT OBSERVED WITH ARCONS FOR EARLY CRAB GIANT PULSES

Energy Technology Data Exchange (ETDEWEB)

Strader, M. J.; Mazin, B. A.; Spiro Jaeger, G. V.; Gwinn, C. R.; Meeker, S. R.; Szypryt, P.; Van Eyken, J. C.; Marsden, D.; Walter, A. B.; Ulbricht, G. [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Johnson, M. D. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); O' Brien, K. [Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Stoughton, C. [Fermilab Center for Particle Astrophysics, Batavia, IL 60510 (United States); Bumble, B. [NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91125 (United States)

2013-12-10

We observe an extraordinary link in the Crab pulsar between the enhancement of an optical pulse and the timing of the corresponding giant radio pulse. At optical through infrared wavelengths, our observations use the high time resolution of ARray Camera for Optical to Near-IR Spectrophotometry, a unique superconducting energy-resolving photon-counting array at the Palomar 200 inch telescope. At radio wavelengths, we observe with the Robert C. Byrd Green Bank Telescope and the Green Bank Ultimate Pulsar Processing Instrument backend. We see an 11.3% ± 2.5% increase in peak optical flux for pulses that have an accompanying giant radio pulse arriving near the peak of the optical main pulse, in contrast to a 3.2% ± 0.5% increase when an accompanying giant radio pulse arrives soon after the optical peak. We also observe that the peak of the optical main pulse is 2.8% ± 0.8% enhanced when there is a giant radio pulse accompanying the optical interpulse. We observe no statistically significant spectral differences between optical pulses accompanied by and not accompanied by giant radio pulses. Our results extend previous observations of optical-radio correlation to the time and spectral domains. Our refined temporal correlation suggests that optical and radio emission are indeed causally linked, and the lack of spectral differences suggests that the same mechanism is responsible for all optical emission.

EXCESS OPTICAL ENHANCEMENT OBSERVED WITH ARCONS FOR EARLY CRAB GIANT PULSES

International Nuclear Information System (INIS)

Strader, M. J.; Mazin, B. A.; Spiro Jaeger, G. V.; Gwinn, C. R.; Meeker, S. R.; Szypryt, P.; Van Eyken, J. C.; Marsden, D.; Walter, A. B.; Ulbricht, G.; Johnson, M. D.; O'Brien, K.; Stoughton, C.; Bumble, B.

2013-01-01

We observe an extraordinary link in the Crab pulsar between the enhancement of an optical pulse and the timing of the corresponding giant radio pulse. At optical through infrared wavelengths, our observations use the high time resolution of ARray Camera for Optical to Near-IR Spectrophotometry, a unique superconducting energy-resolving photon-counting array at the Palomar 200 inch telescope. At radio wavelengths, we observe with the Robert C. Byrd Green Bank Telescope and the Green Bank Ultimate Pulsar Processing Instrument backend. We see an 11.3% ± 2.5% increase in peak optical flux for pulses that have an accompanying giant radio pulse arriving near the peak of the optical main pulse, in contrast to a 3.2% ± 0.5% increase when an accompanying giant radio pulse arrives soon after the optical peak. We also observe that the peak of the optical main pulse is 2.8% ± 0.8% enhanced when there is a giant radio pulse accompanying the optical interpulse. We observe no statistically significant spectral differences between optical pulses accompanied by and not accompanied by giant radio pulses. Our results extend previous observations of optical-radio correlation to the time and spectral domains. Our refined temporal correlation suggests that optical and radio emission are indeed causally linked, and the lack of spectral differences suggests that the same mechanism is responsible for all optical emission

Cryogenic system design for a compact tokamak reactor

International Nuclear Information System (INIS)

Slack, D.S.; Kerns, J.A.; Miller, J.R.

1988-01-01

The International Tokamak Engineering Reactor (ITER) is a program presently underway to design a next-generation tokamak reactor. The cryogenic system for this reactor must meet unusual and new requirements. Unusually high heat loads (100 kW at 4.5 K) must be handled because neutron shielding has been limited to save space in the reactor core. Also, large variations in the cryogenics loads occur over short periods of time because of the pulsed nature of some of the operating scenarios. This paper describes a workable cryogenic system design for a compact tokamak reactor such as ITER. A design analysis is presented dealing with a system that handles transient loads, coil quenches, reactor cool-down and the effect of variations in helium-supply temperatures on the cryogenic stability of the coils. 5 refs., 4 figs., 1 tab

Sensitivity of new detection method for ultra-low frequency gravitational waves with pulsar spin-down rate statistics

Science.gov (United States)

Yonemaru, Naoyuki; Kumamoto, Hiroki; Takahashi, Keitaro; Kuroyanagi, Sachiko

2018-04-01

A new detection method for ultra-low frequency gravitational waves (GWs) with a frequency much lower than the observational range of pulsar timing arrays (PTAs) was suggested in Yonemaru et al. (2016). In the PTA analysis, ultra-low frequency GWs (≲ 10-10 Hz) which evolve just linearly during the observation time span are absorbed by the pulsar spin-down rates since both have the same effect on the pulse arrival time. Therefore, such GWs cannot be detected by the conventional method of PTAs. However, the bias on the observed spin-down rates depends on relative direction of a pulsar and GW source and shows a quadrupole pattern in the sky. Thus, if we divide the pulsars according to the position in the sky and see the difference in the statistics of the spin-down rates, ultra-low frequency GWs from a single source can be detected. In this paper, we evaluate the potential of this method by Monte-Carlo simulations and estimate the sensitivity, considering only the "Earth term" while the "pulsar term" acts like random noise for GW frequencies 10-13 - 10-10 Hz. We find that with 3,000 milli-second pulsars, which are expected to be discovered by a future survey with the Square Kilometre Array, GWs with the derivative of amplitude of about 3 × 10^{-19} {s}^{-1} can in principle be detected. Implications for possible supermassive binary black holes in Sgr* and M87 are also given.

Gamma-Ray Pulsar Studies With GLAST

Energy Technology Data Exchange (ETDEWEB)

Thompson, D.J.; /NASA, Goddard

2011-11-23

Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies.

XMM-NEWTON OBSERVATION OF THE VERY OLD PULSAR J0108-1431

Energy Technology Data Exchange (ETDEWEB)

Posselt, B.; Arumugasamy, P.; Pavlov, G. G. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Manchester, R. N.; Shannon, R. M. [CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710 (Australia); Kargaltsev, O., E-mail: posselt@psu.edu [Department of Physics, The George Washington University, Washington, DC 20052 (United States)

2012-12-20

We report on an X-ray observation of the 166 Myr old radio pulsar J0108-1431 with XMM-Newton. The X-ray spectrum can be described by a power-law model with a relatively steep photon index {Gamma} Almost-Equal-To 3 or by a combination of thermal and non-thermal components, e.g., a power-law component with fixed photon index {Gamma} = 2 plus a blackbody component with a temperature of kT = 0.11 keV. The two-component model appears more reasonable considering different estimates for the hydrogen column density N{sub H}. The non-thermal X-ray efficiency in the single power-law model is {eta}{sup PL}{sub 1-10{sub keV}}= L{sup PL}{sub 1-10{sub keV}}/ E-dot {approx}0.003, higher than in most other X-ray-detected pulsars. In the case of the combined model, the non-thermal and thermal X-ray efficiencies are even higher, {eta}{sup PL}{sub 1-10{sub keV}}{approx}{eta}{sup bb}{sub PC}{approx}0.006. We detected X-ray pulsations at the radio period of P Almost-Equal-To 0.808 s with significance of Almost-Equal-To 7{sigma}. The pulse shape in the folded X-ray light curve (0.15-2 keV) is asymmetric, with statistically significant contributions from up to five leading harmonics. Pulse profiles at two different energy ranges differ slightly: the profile is asymmetric at low energies, 0.15-1 keV, while at higher energies, 1-2 keV, it has a nearly sinusoidal shape. The radio pulse peak leads the 0.15-2 keV X-ray pulse peak by {phi} = 0.06 {+-} 0.03.

Particle acceleration by pulsars

International Nuclear Information System (INIS)

Arons, Jonathan.

1980-06-01

The evidence that pulsars accelerate relativistic particles is reviewed, with emphasis on the γ-ray observations. The current state of knowledge of acceleration in strong waves is summarized, with emphasis on the inability of consistent theories to accelerate very high energy particles without converting too much energy into high energy photons. The state of viable models for pair creation by pulsars is summarized, with the conclusion that pulsars very likely lose rotational energy in winds instead of in superluminous strong waves. The relation of the pair creation models to γ-ray observations and to soft X-ray observations of pulsars is outlined, with the conclusion that energetically viable models may exist, but none have yet yielded useful agreement with the extant data. Some paths for overcoming present problems are discussed. The relation of the favored models to cosmic rays is discussed. It is pointed out that the pairs made by the models may have observable consequences for observation of positrons in the local cosmic ray flux and for observations of the 511 keV line from the interstellar medium. Another new point is that asymmetry of plasma supply from at least one of the models may qualitatively explain the gross asymmetry of the X-ray emission from the Crab nebula. It is also argued that acceleration of cosmic ray nuclei by pulsars, while energetically possible, can occur only at the boundary of the bubbles blown by the pulsars, if the cosmic ray composition is to be anything like that of the known source spectrum

Pulsar populations and their evolution

International Nuclear Information System (INIS)

Narayan, R.; Ostriker, J.P.

1990-01-01

Luminosity models are developed, and an attempt is made to answer fundamental questions regarding the statistical properties of pulsars, on the basis of a large data base encompassing the periods, period derivatives, radio luminosities, vertical Galactic heights, and transverse velocities, for a homogeneous sample of 301 pulsars. A probability is established for two pulsar subpopulations, designated F and S, which are distinguished primarily on the basis of kinematic properties. The two populations are of comparable size, with the F population having an overall birth-rate close to 1 in 200 years in the Galaxy, with the less certain S pulsar birth-rate not higher than that of the F population. 51 refs

The Green Bank Northern Celestial Cap Pulsar Survey. II. The Discovery and Timing of 10 Pulsars

Science.gov (United States)

Kawash, A. M.; McLaughlin, M. A.; Kaplan, D. L.; DeCesar, M. E.; Levin, L.; Lorimer, D. R.; Lynch, R. S.; Stovall, K.; Swiggum, J. K.; Fonseca, E.; Archibald, A. M.; Banaszak, S.; Biwer, C. M.; Boyles, J.; Cui, B.; Dartez, L. P.; Day, D.; Ernst, S.; Ford, A. J.; Flanigan, J.; Heatherly, S. A.; Hessels, J. W. T.; Hinojosa, J.; Jenet, F. A.; Karako-Argaman, C.; Kaspi, V. M.; Kondratiev, V. I.; Leake, S.; Lunsford, G.; Martinez, J. G.; Mata, A.; Matheny, T. D.; Mcewen, A. E.; Mingyar, M. G.; Orsini, A. L.; Ransom, S. M.; Roberts, M. S. E.; Rohr, M. D.; Siemens, X.; Spiewak, R.; Stairs, I. H.; van Leeuwen, J.; Walker, A. N.; Wells, B. L.

2018-04-01

We present timing solutions for 10 pulsars discovered in 350 MHz searches with the Green Bank Telescope. Nine of these were discovered in the Green Bank Northern Celestial Cap survey and one was discovered by students in the Pulsar Search Collaboratory program during an analysis of drift-scan data. Following the discovery and confirmation with the Green Bank Telescope, timing has yielded phase-connected solutions with high-precision measurements of rotational and astrometric parameters. Eight of the pulsars are slow and isolated, including PSR J0930‑2301, a pulsar with a nulling fraction lower limit of ∼30% and a nulling timescale of seconds to minutes. This pulsar also shows evidence of mode changing. The remaining two pulsars have undergone recycling, accreting material from binary companions, resulting in higher spin frequencies. PSR J0557‑2948 is an isolated, 44 ms pulsar that has been partially recycled and is likely a former member of a binary system that was disrupted by a second supernova. The paucity of such so-called “disrupted binary pulsars” (DRPs) compared to double neutron star (DNS) binaries can be used to test current evolutionary scenarios, especially the kicks imparted on the neutron stars in the second supernova. There is some evidence that DRPs have larger space velocities, which could explain their small numbers. PSR J1806+2819 is a 15 ms pulsar in a 44-day orbit with a low-mass white dwarf companion. We did not detect the companion in archival optical data, indicating that it must be older than 1200 Myr.

Advanced statistics for tokamak transport colinearity and tokamak to tokamak variation

International Nuclear Information System (INIS)

Riedel, K.S.

1989-03-01

This is a compendium of three separate articles on the statistical analysis of tokamak transport. The first article is an expository introduction to advanced statistics and scaling laws. The second analyzes two important problems of tokamak data---colinearity and tokamak to tokamak variation in detail. The third article generalizes the Swamy random coefficient model to the case of degenerate matrices. Three papers have been processed separately

Spectral properties of 441 radio pulsars

Science.gov (United States)

Jankowski, F.; van Straten, W.; Keane, E. F.; Bailes, M.; Barr, E. D.; Johnston, S.; Kerr, M.

2018-02-01

We present a study of the spectral properties of 441 pulsars observed with the Parkes radio telescope near the centre frequencies of 728, 1382 and 3100 MHz. The observations at 728 and 3100 MHz were conducted simultaneously using the dual-band 10-50 cm receiver. These high-sensitivity, multifrequency observations provide a systematic and uniform sample of pulsar flux densities. We combine our measurements with spectral data from the literature in order to derive the spectral properties of these pulsars. Using techniques from robust regression and information theory, we classify the observed spectra in an objective, robust and unbiased way into five morphological classes: simple or broken power law, power law with either low- or high-frequency cut-off and log-parabolic spectrum. While about 79 per cent of the pulsars that could be classified have simple power-law spectra, we find significant deviations in 73 pulsars, 35 of which have curved spectra, 25 with a spectral break and 10 with a low-frequency turn-over. We identify 11 gigahertz-peaked spectrum (GPS) pulsars, with 3 newly identified in this work and 8 confirmations of known GPS pulsars; 3 others show tentative evidence of GPS, but require further low-frequency measurements to support this classification. The weighted mean spectral index of all pulsars with simple power-law spectra is -1.60 ± 0.03. The observed spectral indices are well described by a shifted log-normal distribution. The strongest correlations of spectral index are with spin-down luminosity, magnetic field at the light-cylinder and spin-down rate. We also investigate the physical origin of the observed spectral features and determine emission altitudes for three pulsars.

Aspects of pulsar evolution

International Nuclear Information System (INIS)

Fujimura, F.S.; Kennel, C.F.

1980-01-01

We consider pulsar statistics from the point of view of generalized evolutionary equations that assume that pulsar torques diminish exponentially with a decay-time constant T, to be determined empirically. Decay or alignment of the neutron-star magnetic moment, or a combination, may cause the torque to diminish with time. The Sturrock-Ruderman-Sutherland pair-production model provides a quantitative way to calculate pulsar lifetimes. Different test, which use th data in partially independent ways and involve differnt assumptions, consistently suggest that T is less than a million years and may be as short as several hundred thousand years

Comparative studies of stellarator and tokamak transport

Energy Technology Data Exchange (ETDEWEB)

Stroth, U; Burhenn, R; Geiger, J; Giannone, L.; Hartfuss, H J; Kuehner, G; Ledl, L; Simmet, E E; Walter, H [Max-Planck-Inst. fuer Plasmaphysik, IPP-Euratom Association, Garching (Germany); ECRH Team; W7-AS Team

1997-09-01

Transport properties in the W7-AS stellarator and in tokamaks are compared. The parameter dependences and the absolute values of the energy confinement time are similar. Indications are found that the density dependence, which is usually observed in stellarator confinement, can vanish above a critical density. The density dependence in stellarators seems to be similar to that in the linear ohmic confinement regime, which, in small tokamaks, extends to high density values, too. Because of the similarity in the gross confinement properties, transport in stellarators and tokamaks should not be dominated by the parameters which are very different in the two concepts, i.e. magnetic shear, major rational values of the rotational transform and plasma current. A difference in confinement is that there exists evidence for pinches in the particle and, possibly, energy transport channels in tokamaks whereas in stellarators no pinches have been observed, so far. In order to study the effect of plasma current and toroidal electric fields, stellarator discharges were carried out with an increasing amount of plasma current. From these experiments, no clear evidence of a connection of pinches with these parameters is found. The transient response in W7-AS plasmas can be described in terms of a non-local model. As in tokamaks, also cold pulse experiments in W7-AS indicate the importance of non-local transport. (author). 8 refs, 5 figs.

Super high field ohmically heated tokamak operation

International Nuclear Information System (INIS)

Cohn, D.R.; Bromberg, L.; Leclaire, R.J.; Potok, R.E.; Jassby, D.L.

1986-01-01

The authors discuss a super high field mode of tokamak operation that uses ohmic heating or near ohmic heating to ignition. The super high field mode of operation uses very high values of Β/sup 2/α, where Β is the magnetic field and a is the minor radius (Β/sup 2/α > 100 T/sup 2/m). We analyze copper magnet devices with major radii from 1.7 to 3.0 meters. Minimizing or eliminating the need for auxiliary heating has the potential advantages of reducing uncertainty in extrapolating the energy confinement time of current tokamak devices, and reducing engineering problems associated with large auxiliary heating requirements. It may be possible to heat relatively short pulse, inertially cooled tokamaks to ignition with ohmic power alone. However, there may be advantages in using a very small amount of auxiliary power (less than the ohmic heating power) to boost the ohmic heating and provide a faster start-up, expecially in relatively compact devices

Review of tokamak power reactor and blanket designs in the United States

International Nuclear Information System (INIS)

Baker, C.; Brooks, J.; Ehst, D.; Gohar, Y.; Smith, D.; Sze, D.

1986-01-01

The last major conceptual design study of a tokamak power reactor in the United States was STARFIRE which was carried out in 1979-1980. Since that time US studies have concentrated on engineering test reactors, demonstration reactors, parametric systems studies, scoping studies, and studies of selected critical issues such as pulsed vs. steady-state operation and blanket requirements. During this period, there have been many advancements in tokamak physics and reactor technology, and there has also been a recognition that it is desirable to improve the tokamak concept as a commercial power reactor candidate. During 1984-1985 several organizations participated in the Tokamak Power Systems Study (TPSS) with the objective of developing ideas for improving the tokamak as a power reactor. Also, the US completed a comprehensive Blanket Comparison and Selection Study which formed the basis for further studies on improved blankets for fusion reactors

A current-pulsed power supply with rapid rising and falling edges for magnetic perturbation coils on the J-TEXT tokamak

International Nuclear Information System (INIS)

Yan, M.X.; Rao, B.; Ding, Y.H.; Hu, Q.M.; Hu, F.R.; Li, D.; Li, M.; Ji, X.K.; Xu, G.; Zheng, W.; Jiang, Z.H.

2017-01-01

Highlights: • The power supply is required to have rapid rising and falling edges. • A modified topology based on the buck chopper of current-pulsed power supply is presented and analyzed. • An entity meeting the electrical requirements has been constructed. • The spike voltage of IGBT is qualitatively analyzed. - Abstract: This study presents the design and principle of a current-pulsed power supply (CPPS) for the tearing mode (TM) feedback control of the J-TEXT tokamak. CPPS is a new method of stabilizing large magnetic islands and accelerating mode rotation through the use of modulated magnetic perturbation. In this application, continuous magnetic perturbation pulse trains with frequency of 1 kHz to kHz, amplitude of 0.25 G, and duty ratio of 20%–50% are required generating via in-vessel magnetic coils. A modified topology based on buck chopper is raised to satisfy the demands of inductive load. This modified topology is characterized by high frequency, rapid rising and falling edges, and large amplitude of current pulses. Appropriate RCD snubber circuit is applied to protect the Insulated Gate Bipolar Transistor (IGBT) switch device. Equipment with peak current that reaches 1 kA, frequency that ranges from 1 kHz to 3 kHz, and rising and falling time within 100 μs was constructed and applied to physical experiment.

A current-pulsed power supply with rapid rising and falling edges for magnetic perturbation coils on the J-TEXT tokamak

Energy Technology Data Exchange (ETDEWEB)

Yan, M.X. [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Rao, B., E-mail: borao@hust.edu.cn [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Ding, Y.H.; Hu, Q.M.; Hu, F.R.; Li, D.; Li, M.; Ji, X.K.; Xu, G.; Zheng, W.; Jiang, Z.H. [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)

2017-02-15

Highlights: • The power supply is required to have rapid rising and falling edges. • A modified topology based on the buck chopper of current-pulsed power supply is presented and analyzed. • An entity meeting the electrical requirements has been constructed. • The spike voltage of IGBT is qualitatively analyzed. - Abstract: This study presents the design and principle of a current-pulsed power supply (CPPS) for the tearing mode (TM) feedback control of the J-TEXT tokamak. CPPS is a new method of stabilizing large magnetic islands and accelerating mode rotation through the use of modulated magnetic perturbation. In this application, continuous magnetic perturbation pulse trains with frequency of 1 kHz to kHz, amplitude of 0.25 G, and duty ratio of 20%–50% are required generating via in-vessel magnetic coils. A modified topology based on buck chopper is raised to satisfy the demands of inductive load. This modified topology is characterized by high frequency, rapid rising and falling edges, and large amplitude of current pulses. Appropriate RCD snubber circuit is applied to protect the Insulated Gate Bipolar Transistor (IGBT) switch device. Equipment with peak current that reaches 1 kA, frequency that ranges from 1 kHz to 3 kHz, and rising and falling time within 100 μs was constructed and applied to physical experiment.

A New Standard Pulsar Magnetosphere

Science.gov (United States)

Contopoulos, Ioannis; Kalapotharakos, Constantinos; Kazanas, Demosthenes

2014-01-01

In view of recent efforts to probe the physical conditions in the pulsar current sheet, we revisit the standard solution that describes the main elements of the ideal force-free pulsar magnetosphere. The simple physical requirement that the electric current contained in the current layer consists of the local electric charge moving outward at close to the speed of light yields a new solution for the pulsar magnetosphere everywhere that is ideal force-free except in the current layer. The main elements of the new solution are as follows: (1) the pulsar spindown rate of the aligned rotator is 23% larger than that of the orthogonal vacuum rotator; (2) only 60% of the magnetic flux that crosses the light cylinder opens up to infinity; (3) the electric current closes along the other 40%, which gradually converges to the equator; (4) this transfers 40% of the total pulsar spindown energy flux in the equatorial current sheet, which is then dissipated in the acceleration of particles and in high-energy electromagnetic radiation; and (5) there is no separatrix current layer. Our solution is a minimum free-parameter solution in that the equatorial current layer is electrostatically supported against collapse and thus does not require a thermal particle population. In this respect, it is one more step toward the development of a new standard solution. We discuss the implications for intermittent pulsars and long-duration gamma-ray bursts. We conclude that the physical conditions in the equatorial current layer determine the global structure of the pulsar magnetosphere.

Prospects for neutron star equation of state constraints using ''recycled'' millisecond pulsars

Energy Technology Data Exchange (ETDEWEB)

Bogdanov, Slavko [Columbia University, Columbia Astrophysics Laboratory, New York, NY (United States)

2016-02-15

''Recycled'' millisecond pulsars are a variety of rapidly spinning neutron stars that typically show thermal X-ray radiation due to the heated surface of their magnetic polar caps. Detailed numerical modeling of the rotation-induced thermal X-ray pulsations observed from recycled millisecond pulsars, including all relevant relativistic and stellar atmospheric effects, has been identified as a promising approach towards an astrophysical determination of the true neutron star mass-radius relation, and by extension the state of cold matter at densities exceeding those of atomic nuclei. Herein, I review the basic model and methodology commonly used to extract information regarding neutron star structure from the pulsed X-ray radiation observed from millisecond pulsars. I also summarize the results of past X-ray observations of these objects and the prospects for precision neutron star mass-radius measurements with the upcoming Neutron Star Interior Composition Explorer (NICER) X-ray timing mission. (orig.)

Pulsars: gigantic nuclei

International Nuclear Information System (INIS)

Xu, Renxin

2011-01-01

What is the real nature of pulsars? This is essentially a question of the fundamental strong interaction between quarks at low-energy scale and hence of the non-perturbative quantum chromo-dynamics, the solution of which would certainly be meaningful for us to understand one of the seven millennium prize problems (i.e., "Yang-Mills Theory") named by the Clay Mathematical Institute. After a historical note, it is argued here that a pulsar is very similar to an extremely big nucleus, but is a little bit different from the gigantic nucleus speculated 80 years ago by L. Landau. The paper demonstrates the similarity between pulsars and gigantic nuclei from both points of view: the different manifestations of compact stars and the general behavior of the strong interaction. (author)

Characterization of the Tokamak Novillo in cleaning regime

International Nuclear Information System (INIS)

Lopez C, R.; Melendez L, L.; Valencia A, R.; Chavez A, E.; Colunga S, S.; Gaytan G, E.

1992-02-01

In this work the obtained results of the investigation about the experimental characterization of those low energy pulsed discharges of the Tokamak Novillo are reported. With this it is possible to fix the one operation point but appropriate of the Tokamak to condition the chamber in the smallest possible time for the cleaning discharges regime before beginning the main discharge. The characterization of the cleaning discharges in those Tokamaks is an unique process and characteristic of each device, since the good points of operation are consequence of those particularities of the design of the machine. In the case of the Tokamak Novillo, besides characterizing it a contribution is made to the cleaning discharges regime which consists on the one product of the current peak to peak of plasma by the duration of the discharge Ip t like reference parameter for the optimization of the operation of the device in the cleaning discharge regime. The maximum value of the parameter I (p) t, under different work conditions, allowed to find the good operation point to condition the discharges chamber of the Tokamak Novillo in short time and to arrive to a regime in which is not necessary the preionization for the obtaining of the cleaning discharges. (Author)

The spheric tokamak programme at Culham

International Nuclear Information System (INIS)

Sykes, A.

1999-01-01

The Spherical Tokamak (ST) is the low aspect ratio limit of the conventional tokamak, and appears to offer attractive physics properties in a simpler device. The START (Small Tight Aspect Ratio Tokamak) experiment provided the world's first demonstration of the properties of hot plasmas in an ST configuration, and was operational at Culham from January 1991 to March 1998, obtaining plasma current of up to 300 kA and pulse durations of ∼ 50 ms. Its successor, MAST is scheduled to obtain first plasma in Autumn 1998 and is a purpose built, high vacuum machine designed to have a tenfold increase in plasma volume with plasma currents up to 2 MA. Current drive and heating will be by a combination of induction-compression as on START, a high-performance central solenoid, 1.5 MW ECRH and 5 MW of Neutral Beam Injection. The promising results from START are reviewed, and the many challenges posed for the next generation of purpose-built STs (such as MAST) are described. (author)

The International Pulsar Timing Array project: using pulsars as a gravitational wave detector

NARCIS (Netherlands)

Hobbs, G.; Archibald, A.; Arzoumanian, Z.; Backer, D.; Bailes, M.; Bhat, N.D.R.; Burgay, M.; Burke-Spolaor, S.; Champion, D.; Cognard, I.; Coles, W.; Cordes, J.; Demorest, P.; Desvignes, G.; Ferdman, R.D.; Finn, L.; Freire, P.; Gonzalez, M.; Hessels, J.; Hotan, A.; Janssen, G.; Jenet, F.; Jessner, A.; Jordan, C.; Kaspi, V.; Kramer, M.; Kondratiev, V.; Lazio, J.; Lazaridis, K.; Lee, K.J.; Levin, Y.; Lommen, A.; Lorimer, D.; Lynch, R.; Lyne, A.; Manchester, R.; McLaughlin, M.; Nice, D.; Oslowski, S.; Pilia, M.; Possenti, A.; Purver, M.; Ransom, S.; Reynolds, J.; Sanidas, S.; Sarkissian, J.; Sesana, A.; Shannon, R.; Siemens, X.; Stairs, I.; Stappers, B.; Stinebring, D.; Theureau, G.; van Haasteren, R.; van Straten, W.; Verbiest, J.P.W.; Yardley, D.R.B.; You, X.P.

2010-01-01

The International Pulsar Timing Array project combines observations of pulsars from both northern and southern hemisphere observatories with the main aim of detecting ultra-low frequency (similar to 10(-9)-10(-8) Hz) gravitational waves. Here we introduce the project, review the methods used to

Gamma ray emission from pulsars

International Nuclear Information System (INIS)

Salvati, M.; Massaro, E.

1978-01-01

A model for the production of gamma rays in a pulsar environment is presented, together with numerical computations fitted to the observations of PSR 0833-45. It is assumed that the primary particles are accelerated close to the star surface and then injected along the open field lines, which cause them to emit curvature radiation. The equation describing the particles' braking is integrated exactly up to the first order in the pulsar rotational frequency, and the transfer problem for the curvature photons is solved with the aberration, the Doppler shif, and the pair production absorption being taken into account. The latter effect is due not only to the transverse component of the magnetic field, but also to the electric field induced by the rotation. The synchrotron radiation emitted by the secondary particles is also included, subject to the 'on-the-spot' approximation. It is found that the observed gamma rays originate in the innermost regions of the magnetosphere, where the open lines' bundle is narrow and the geometrical beaming is effective. As shown by the computed pulse profiles, the duty cycle turns out to be equal to a few percent, comparable to the one of PSR 0833-45. The averaged spectra indicate that a substantial fraction of the primary photons do outlive the interaction with the magnetisphere; furthermore, the agreement in shape with the observational curves suggests that the acceleration output is fiarly close to a monoenergetic beam of particles. (orig.) [de

Two-stream instability in pulsar magnetospheres

International Nuclear Information System (INIS)

Usov, V.V.

1987-01-01

If the electron-positron plasma flow from the pulsar environment is stationary, the two-stream instability does not have enough time to develop in the pulsar magnetosphere. In that case the outflowing electron-positron plasma gathers into separate clouds. The clouds move along magnetic field lines and disperse as they go farther from the pulsar. At a distance of about 10 to the 8th cm from the pulsar surface, the high-energy particles of a given cloud catch up with the low-energy particles that belong to the cloud going ahead of it. In this region of a pulsar magnetosphere, the energy distribution of plasma particles is two-humped, and a two-stream instability may develop. The growth rate of the instability is quite sufficient for its development. 17 references

Relativistic spin precession in the double pulsar.

Science.gov (United States)

Breton, Rene P; Kaspi, Victoria M; Kramer, Michael; McLaughlin, Maura A; Lyutikov, Maxim; Ransom, Scott M; Stairs, Ingrid H; Ferdman, Robert D; Camilo, Fernando; Possenti, Andrea

2008-07-04

The double pulsar PSR J0737-3039A/B consists of two neutron stars in a highly relativistic orbit that displays a roughly 30-second eclipse when pulsar A passes behind pulsar B. Describing this eclipse of pulsar A as due to absorption occurring in the magnetosphere of pulsar B, we successfully used a simple geometric model to characterize the observed changing eclipse morphology and to measure the relativistic precession of pulsar B's spin axis around the total orbital angular momentum. This provides a test of general relativity and alternative theories of gravity in the strong-field regime. Our measured relativistic spin precession rate of 4.77 degrees (-0 degrees .65)(+0 degrees .66) per year (68% confidence level) is consistent with that predicted by general relativity within an uncertainty of 13%.

Hidden slow pulsars in binaries

Science.gov (United States)

Tavani, Marco; Brookshaw, Leigh

1993-01-01

The recent discovery of the binary containing the slow pulsar PSR 1718-19 orbiting around a low-mass companion star adds new light on the characteristics of binary pulsars. The properties of the radio eclipses of PSR 1718-19 are the most striking observational characteristics of this system. The surface of the companion star produces a mass outflow which leaves only a small 'window' in orbital phase for the detection of PSR 1718-19 around 400 MHz. At this observing frequency, PSR 1718-19 is clearly observable only for about 1 hr out of the total 6.2 hr orbital period. The aim of this Letter is twofold: (1) to model the hydrodynamical behavior of the eclipsing material from the companion star of PSR 1718-19 and (2) to argue that a population of binary slow pulsars might have escaped detection in pulsar surveys carried out at 400 MHz. The possible existence of a population of partially or totally hidden slow pulsars in binaries will have a strong impact on current theories of binary evolution of neutron stars.

Multi-field plasma sandpile model in tokamaks and applications

Science.gov (United States)

Peng, X. D.; Xu, J. Q.

2016-08-01

A multi-field sandpile model of tokamak plasmas is formulated for the first time to simulate the dynamic process with interaction between avalanche events on the fast/micro time-scale and diffusive transports on the slow/macro time-scale. The main characteristics of the model are that both particle and energy avalanches of sand grains are taken into account simultaneously. New redistribution rules of a sand-relaxing process are defined according to the transport properties of special turbulence which allows the uphill particle transport. Applying the model, we first simulate the steady-state plasma profile self-sustained by drift wave turbulences in the Ohmic discharge of a tokamak. A scaling law as f = a q0 b + c for the relation of both center-density n ( 0 ) and electron (ion) temperatures T e ( 0 ) ( T i ( 0 ) ) with the center-safety-factor q 0 is found. Then interesting work about the nonlocal transport phenomenon observed in tokamak experiments proceeds. It is found that the core electron temperature increases rapidly in response to the edge cold pulse and inversely it decreases in response to the edge heat pulse. The results show that the nonlocal response of core electron temperature depending on the amplitudes of background plasma density and temperature is more remarkable in a range of gas injection rate. Analyses indicate that the avalanche transport caused by plasma drift instabilities with thresholds is a possible physical mechanism for the nonlocal transport in tokamaks. It is believed that the model is capable of being applied to more extensive questions occurring in the transport field.

Selection of radio pulsar candidates using artificial neural networks

OpenAIRE

Eatough, R. P.; Molkenthin, N.; Kramer, M.; Noutsos, A.; Keith, M. J.; Stappers, B. W.; Lyne, A. G.

2010-01-01

Radio pulsar surveys are producing many more pulsar candidates than can be inspected by human experts in a practical length of time. Here we present a technique to automatically identify credible pulsar candidates from pulsar surveys using an artificial neural network. The technique has been applied to candidates from a recent re-analysis of the Parkes multi-beam pulsar survey resulting in the discovery of a previously unidentified pulsar.

Understanding the spectral and timing behaviour of a newly discovered transient X-ray pulsar Swift J0243.6+6124

Science.gov (United States)

Jaisawal, Gaurava K.; Naik, Sachindra; Chenevez, Jérôme

2018-03-01

We present the results obtained from timing and spectral studies of the newly discovered accreting X-ray binary pulsar Swift J0243.6+6124 using Nuclear Spectroscopy Telescope Array observation in 2017 October at a flux level of ˜280 mCrab. Pulsations at 9.854 23(5) s were detected in the X-ray light curves of the pulsar. Pulse profiles of the pulsar were found to be strongly energy dependent. A broad profile at lower energies was found to evolve into a double-peaked profile in ≥ 30 keV. The 3-79 keV continuum spectrum of the pulsar was well described with a negative and positive exponential cutoff or high-energy cutoff power-law models modified with a hot blackbody at ˜3 keV. An iron emission line was also detected at 6.4 keV in the source spectrum. We did not find any signature of cyclotron absorption line in our study. Results obtained from phase-resolved and time-resolved spectroscopy are discussed in the paper.

A Pulsar and a Disk

Science.gov (United States)

Kohler, Susanna

2016-07-01

Recent, unusual X-ray observations from our galactic neighbor, the Small Magellanic Cloud, have led to an interesting model for SXP 214, a pulsar in a binary star system.Artists illustration of the magnetic field lines of a pulsar, a highly magnetized, rotating neutron star. [NASA]An Intriguing BinaryAn X-ray pulsar is a magnetized, rotating neutron star in a binary system with a stellar companion. Material is fed from the companion onto the neutron star, channeled by the objects magnetic fields onto a hotspot thats millions of degrees. This hotspot rotating past our line of sight is what produces the pulsations that we observe from X-ray pulsars.Located in the Small Magellanic Cloud, SXP 214 is a transient X-ray pulsar in a binary with a Be-type star. This star is spinning so quickly that material is thrown off of it to form a circumstellar disk.Recently, a team of authors led by JaeSub Hong (Harvard-Smithsonian Center for Astrophysics) have presented new Chandra X-ray observations of SXP 214, tracking it for 50 ks (~14 hours) in January 2013. These observations reveal some very unexpected behavior for this pulsar.X-ray PuzzleThe energy distribution of the X-ray emission from SXP 214 over time. Dark shades or blue colors indicate high counts, and light shades or yellow colors indicate low counts. Lower-energy X-ray emission appeared only later, after about 20 ks. [Hong et al. 2016]Three interesting pieces of information came from the Chandra observations:SXP 214s rotation period was measured to be 211.5 s an increase in the spin rate since the discovery measurement of a 214-second period. Pulsars usually spin down as they lose angular momentum over time so what caused this one to spin up?Its overall X-ray luminosity steadily increased over the 50 ks of observations.Its spectrum became gradually softer (lower energy) over time; in the first 20 ks, the spectrum only consisted of hard X-ray photons above 3 keV, but after 20 ks, softer X-ray photons below 2 ke

Coherence of burst oscillations and accretion-powered pulsations in the accreting millisecond pulsar XTE J1814-338

NARCIS (Netherlands)

Watts, A.L.; Patruno, A.; van der Klis, M.

2008-01-01

X-ray timing of the accretion-powered pulsations during the 2003 outburst of the accreting millisecond pulsar XTE J1814-338 has revealed variation in the pulse time of arrival residuals. These can be interpreted in several ways, including spin-down and wandering of the fuel impact point around the

DIII-D Advanced Tokamak Research Overview

International Nuclear Information System (INIS)

V.S. Chan; C.M. Greenfield; L.L. Lao; T.C. Luce; C.C. Petty; G.M. Staebler

1999-01-01

This paper reviews recent progress in the development of long-pulse, high performance discharges on the DIII-D tokamak. It is highlighted by a discharge achieving simultaneously β N H of 9, bootstrap current fraction of 0.5, noninductive current fraction of 0.75, and sustained for 16 energy confinement times. The physics challenge has changed in the long-pulse regime. Non-ideal MHD modes are limiting the stability, fast ion driven modes may play a role in fast ion transport which limits the stored energy and plasma edge behavior can affect the global performance. New control tools are being developed to address these issues

High-Energy Pulsar Models: Developments and New Questions

Science.gov (United States)

Venter, C.; Harding, A. K.

2014-01-01

The past few years have seen a major advance in observational knowledge of high-energy (HE) pulsars. The Fermi Large Area Telescope (LAT) and AGILE have increased the number of known gamma-ray pulsars by an order of magnitude, its members being divided roughly equally among millisecond pulsars (MSPs), young radio-loud pulsars, and young radio-quiet pulsars. Many new and diverse emission characteristics are being measured, while radio and X-ray follow-up observations increase the pulsar detection rate and enrich our multiwavelength picture of these extreme sources. The wealth of new data has provided impetus for further development and improvement of existing theoretical pulsar models. Geometric light curve (LC) modelling has uncovered three broad classes into which HE pulsars fall: those where the radio profile leads, is aligned with, or lags the gamma-ray profile. For example, the original MSP and original black widow system are members of the second class, requiring co-located emission regions and thereby breaking with traditional notions of radio emission origin. These models imply narrow accelerator gaps in the outer magnetosphere, indicating copious pair production even in MSP magnetospheres that were previously thought to be pair-starved. The increased quality and variety of the LCs necessitate construction of ever more sophisticated models. We will review progress in global magnetosphere solutions which specify a finite conductivity on field lines above the stellar surface, filling the gap between the standard vacuum and force-free (FF; plasma-filled) models. The possibility of deriving phase-resolved spectra for the brightest pulsars, coupled with the fact that the HE pulsar population is sizable enough to allow sampling of various pulsar geometries, will enable much more stringent testing of future radiation models. Reproduction of the observed phase-resolved behavior of this disparate group will be one of the next frontiers in pulsar science, impacting on

DISCOVERY OF X-RAY PULSATION FROM THE GEMINGA-LIKE PULSAR PSR J2021+4026

Energy Technology Data Exchange (ETDEWEB)

Lin, L. C. C. [General Education Center, China Medical University, Taichung 40402, Taiwan (China); Hui, C. Y.; Seo, K. A., E-mail: cyhui@cnu.ac.kr [Department of Astronomy and Space Science, Chungnam National University, Daejeon (Korea, Republic of); Hu, C. P.; Chou, Y. [Graduate Institute of Astronomy, National Central University, Jhongli 32001, Taiwan (China); Wu, J. H. K.; Huang, R. H. H. [Institute of Astronomy, National Tsing-Hua University, Hsinchu 30013, Taiwan (China); Trepl, L. [Astrophysikalisches Institut und Universitaets-Sternwarte, Universitaet Jena, Schillergaesschen 2-3, D-07745 Jena (Germany); Takata, J.; Wang, Y.; Cheng, K. S. [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (Hong Kong)

2013-06-10

We report the discovery of an X-ray periodicity of {approx}265.3 ms from a deep XMM-Newton observation of the radio-quiet {gamma}-ray pulsar, PSR J2021+4026, located at the edge of the supernova remnant G78.2+2.1 ({gamma}-Cygni). The detected frequency is consistent with the {gamma}-ray pulsation determined by the observation of the Fermi Gamma-ray Space Telescope at the same epoch. The X-ray pulse profile resembles the modulation of a hot spot on the surface of the neutron star. The phase-averaged spectral analysis also suggests that the majority of the observed X-rays have thermal origins. This is the third member in the class of radio-quiet pulsars with significant pulsations detected from both X-ray and {gamma}-ray regimes.

Noise Budget and Interstellar Medium Mitigation Advances in the NANOGrav Pulsar Timing Array

Science.gov (United States)

Dolch, T.; NANOGrav Collaboration; Chatterjee, S.; Cordes, J. M.; Demorest, P. B.; Ellis, J. A.; Jones, M. L.; Lam, M. T.; Lazio, T. J. W.; Levin, L.; McLaughlin, M. A.; Palliyaguru, N. T.; Stinebring, D. R.

2018-02-01

Gravitational wave (GW) detection with pulsar timing arrays (PTAs) requires accurate noise characterization. The noise of our Galactic-scale GW detector has been systematically evaluated by the Noise Budget and Interstellar Medium Mitigation working groups within the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration. Intrinsically, individual radio millisecond pulsars (MSPs) used by NANOGrav can have some degree of achromatic red spin noise, as well as white noise due to pulse phase jitter. Along any given line-of-sight, the ionized interstellar medium contributes chromatic noise through dispersion measure (DM) variations, interstellar scintillation, and scattering. These effects contain both red and white components. In the future, with wideband receivers, the effects of frequency-dependent DM will become important. Having anticipated and measured these diverse sources of detector noise, the NANOGrav PTA remains well-poised to detect low-frequency GWs.

Swinging between rotation and accretion power in a binary millisecond pulsar

Directory of Open Access Journals (Sweden)

Papitto A.

2014-01-01

While accreting mass, the X-ray emission of IGR J18245–2452 varies dramatically on time-scales ranging from a second to a few hours. We interpret a state characterised by a lower flux and pulsed fraction, and by sudden increases of the hardness of the X-ray emission, in terms of the onset of a magnetospheric centrifugal inhibition of the accretion flow. Prospects of finding new members of the newly established class of transitional pulsars are also briefly discussed.

Pulsar velocity observations: Correlations, interpretations, and discussion

International Nuclear Information System (INIS)

Helfand, D.J.; Tademaru, E.

1977-01-01

From an examination of the current sample of 12 pulsars with measured proper motions and the z-distribution of the much larger group of over 80 sources with measured period derivatives, we develop a self-consistent picture of pulsar evolution. The apparent tendency of pulsars to move parallel to the galactic plane is explained as the result of various selection effects. A method for calculating the unmeasurable radial velocity of a pulsar is presented; it is shown that the total space velocities thus obtained are consistent with the assumption of an extreme Population I origin for pulsars which subsequently move away from the plane with a large range of velocities. The time scale for pulsar magnetic field decay is derived from dynamical considerations. A strong correlation of the original pulsar field strength with the magnitude of pulsar velocity is discussed. This results in the division of pulsars into two classes: Class A sources characterized by low space velocities, a small scale height, and low values of P 0 P 0 ; and Class B sources with a large range of velocities (up to 1000 km s -1 ), a much greater scale height, and larger values of initial field strength. It is postulated that Class A sources originate in tight binaries where their impulse acceleration at birth is insufficient to remove them from the system, while the Class B sources arise from single stars or loosely bound binaries and are accelerated to high velocities by their asymmetric radiation force. The evolutionary picture which is developed is shown to be consistent with a number of constraints imposed by supernova rates, the relative frequency of massive binaries and Class A sources, theoretical field-decay times, and the overall pulsar galactic distribution

16 yr of RXTE monitoring of five anomalous X-ray pulsars

Energy Technology Data Exchange (ETDEWEB)

Dib, Rim; Kaspi, Victoria M., E-mail: rim@physics.mcgill.ca, E-mail: vkaspi@physics.mcgill.ca [Department of Physics, McGill University, Montreal, QC H3A 2T8 (Canada)

2014-03-20

We present a summary of the long-term evolution of various properties of the five non-transient anomalous X-ray pulsars (AXPs) 1E 1841–045, RXS J170849.0–400910, 1E 2259+586, 4U 0142+61, and 1E 1048.1–5937, regularly monitored with RXTE from 1996 to 2012. We focus on three properties of these sources: the evolution of the timing, pulsed flux, and pulse profile. We report several new timing anomalies and radiative events, including a putative anti-glitch seen in 1E 2259+586 in 2009, and a second epoch of very large spin-down rate fluctuations in 1E 1048.1–5937 following a large flux outburst. We compile the properties of the 11 glitches and 4 glitch candidates observed from these 5 AXPs between 1996 and 2012. Overall, these monitoring observations reveal several apparent patterns in the behavior of this sample of AXPs: large radiative changes in AXPs (including long-lived flux enhancements, short bursts, and pulse profile changes) are rare, occurring typically only every few years per source; large radiative changes are almost always accompanied by some form of timing anomaly, usually a spin-up glitch; only 20%-30% of timing anomalies are accompanied by any form of radiative change. We find that AXP radiative behavior at the times of radiatively loud glitches is sufficiently similar to suggest common physical origins. The similarity in glitch properties when comparing radiatively loud and radiatively silent glitches in AXPs suggests a common physical origin in the stellar interior. Finally, the overall similarity of AXP and radio pulsar glitches suggests a common physical origin for both phenomena.

Research tokamak system with multi-mode discharges using inverter power supply

International Nuclear Information System (INIS)

Kojima, Hiroki; Kobayashi, Masahiro; Takagi, Makoto; Takamura, Shuichi; Tashiro, Kenji

1999-01-01

In Current Sustaining Tokamak in Nagoya university (CSTN)-IV research tokamak system using a compact 40kHz pulse width modulation (PWM) inverter power supply, which is controlled through LabVIEW program, we construct a new tokamak discharge system with multi-mode including a stable alternating current discharge and a high-repetition high-duty one. These discharge modes can be operated continuously for as long as 60sec. The continuous discharge with long duration is able to simulate the important physical and chemical processes of long time discharges in fusion devices, in which the heat load to the wall and the particle balance in the plasma-wall system are crucial topics in order to realize a long pulse fusion reactor, like ITER. Employing ergodic divertor (ED) is one of tools to control the particle balance and the heat load to the wall. In addition, we installed another inverter power supply to generate a rotating magnetic perturbation for dynamic ergodic divertor (DED) with the appropriate measurement system so that we may carry out experiments on heat and particle control with DED at long time operation. (author)

Tiny Tremors to Titanic Explosions: Tackling Transients in Anomalous X-Ray Pulsars

Science.gov (United States)

Kaspi, Victoria

We are requesting the target-of-oppurtunity (ToO) component of an ongoing, successful, long-term RXTE monitoring campaign of anomalous X- ray pulsars (AXPs). Their nature had been a mystery, but with our discoveries of X-ray bursts from AXPs, there is compelling evidence that they are young, isolated, ultra-magnetized neutron stars or "magnetars." We request ToO observations of any of the known and candidate AXPs as well as of any newly discovered AXPs should they exhibit anomalous behavior of one or more of the following types: bursts, significant sudden pulse profile changes, glitches or other rotational anomalies, or pulse fractions changes. These observations will allow us to answer basic physical questions about neutron star structure.

Pulsar-Driven Jets in Supernovae, Gamma-Ray Bursts, and the Universe

Directory of Open Access Journals (Sweden)

John Middleditch

2012-01-01

Full Text Available The bipolarity of Supernova 1987A can be understood through its very early light curve from the CTIO 0.4 m telescope and IUE FES and following speckle observations of the “Mystery Spot”. These indicate a beam/jet of light/particles, with initial collimation factors >104 and velocities >0.95 c, involving up to 10−5 M⊙ interacting with circumstellar material. These can be produced by a model of pulsar emission from polarization currents induced/(modulated faster than c beyond the pulsar light cylinder by the periodic electromagnetic field (supraluminally induced polarization currents (SLIP. SLIP accounts for the disruption of supernova progenitors and their anomalous dimming at cosmological distances, jets from Sco X-1 and SS 433, the lack/presence of pulsations from the high-/low-luminosity low-mass X-ray binaries, and long/short gamma-ray bursts, and it predicts that their afterglows are the pulsed optical-/near-infrared emission associated with these pulsars. SLIP may also account for the TeV e+/e− results from PAMELA and ATIC, the WMAP “Haze”/Fermi “Bubbles,” and the r-process. SLIP jets from SNe of the first stars may allow galaxies to form without dark matter and explain the peculiar nongravitational motions between pairs of distant galaxies observed by GALEX.

The High Time Resolution Universe Pulsar Survey - XII. Galactic plane acceleration search and the discovery of 60 pulsars

Science.gov (United States)

Ng, C.; Champion, D. J.; Bailes, M.; Barr, E. D.; Bates, S. D.; Bhat, N. D. R.; Burgay, M.; Burke-Spolaor, S.; Flynn, C. M. L.; Jameson, A.; Johnston, S.; Keith, M. J.; Kramer, M.; Levin, L.; Petroff, E.; Possenti, A.; Stappers, B. W.; van Straten, W.; Tiburzi, C.; Eatough, R. P.; Lyne, A. G.

2015-07-01

We present initial results from the low-latitude Galactic plane region of the High Time Resolution Universe pulsar survey conducted at the Parkes 64-m radio telescope. We discuss the computational challenges arising from the processing of the terabyte-sized survey data. Two new radio interference mitigation techniques are introduced, as well as a partially coherent segmented acceleration search algorithm which aims to increase our chances of discovering highly relativistic short-orbit binary systems, covering a parameter space including potential pulsar-black hole binaries. We show that under a constant acceleration approximation, a ratio of data length over orbital period of ≈0.1 results in the highest effectiveness for this search algorithm. From the 50 per cent of data processed thus far, we have redetected 435 previously known pulsars and discovered a further 60 pulsars, two of which are fast-spinning pulsars with periods less than 30 ms. PSR J1101-6424 is a millisecond pulsar whose heavy white dwarf (WD) companion and short spin period of 5.1 ms indicate a rare example of full-recycling via Case A Roche lobe overflow. PSR J1757-27 appears to be an isolated recycled pulsar with a relatively long spin period of 17 ms. In addition, PSR J1244-6359 is a mildly recycled binary system with a heavy WD companion, PSR J1755-25 has a significant orbital eccentricity of 0.09 and PSR J1759-24 is likely to be a long-orbit eclipsing binary with orbital period of the order of tens of years. Comparison of our newly discovered pulsar sample to the known population suggests that they belong to an older population. Furthermore, we demonstrate that our current pulsar detection yield is as expected from population synthesis.

A Search for Debris Disks Around Variable Pulsars

Science.gov (United States)

Shannon, Ryan; Cordes, J.; Lazio, J.; Kramer, M.; Lyne, A.

2009-01-01

After a supernova explosion, a modest amount of material will fall back and form a disk surrounding the resultant neutron star. This material can aggregate into rocky debris and the disk can be stable for the entire 10 million year lifetime of a canonical (non-recycled) radio pulsar. Previously, we developed a model that unifies the different classes of radio variability observed in many older pulsars. In this model, rocky material migrates inwards towards the neutron star and is ablated inside the pulsar magnetosphere. This material alters the electrodynamics in the magnetosphere which can cause the observed quiescent and bursting states observed in nulling pulsars, intermittent pulsars, and rotating radio transients. With this model in mind, we observed three nulling pulsars and one intermittent pulsar that are good candidates to host debris disks detectable by the Spitzer IRAC. Here we report how our IRAC observations constrain disk geometry, with particular emphasis on configurations that can provide the in-fall rate to cause the observed radio variability. We place these observations in the context of other searches for debris disks around neutron stars, which had studied either very young or very old (recycled) pulsars. By observing older canonical pulsars, all major classes of radio pulsars have been observed, and we can assess the presence of debris disks as a function of pulsar type. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.

Radio Detection of the Fermi-LAT Blind Search Millisecond Pulsar J1311-3430

Science.gov (United States)

Ray, P. S.; Ransom, S. M.; Cheung, C. C.; Giroletti, M.; Cognard, I.; Camilo, F.; Bhattacharyya, B.; Roy, J.; Romani, R. W.; Ferrara, E. C.;

Optimized blind gamma-ray pulsar searches at fixed computing budget

International Nuclear Information System (INIS)

Pletsch, Holger J.; Clark, Colin J.

2014-01-01

The sensitivity of blind gamma-ray pulsar searches in multiple years worth of photon data, as from the Fermi LAT, is primarily limited by the finite computational resources available. Addressing this 'needle in a haystack' problem, here we present methods for optimizing blind searches to achieve the highest sensitivity at fixed computing cost. For both coherent and semicoherent methods, we consider their statistical properties and study their search sensitivity under computational constraints. The results validate a multistage strategy, where the first stage scans the entire parameter space using an efficient semicoherent method and promising candidates are then refined through a fully coherent analysis. We also find that for the first stage of a blind search incoherent harmonic summing of powers is not worthwhile at fixed computing cost for typical gamma-ray pulsars. Further enhancing sensitivity, we present efficiency-improved interpolation techniques for the semicoherent search stage. Via realistic simulations we demonstrate that overall these optimizations can significantly lower the minimum detectable pulsed fraction by almost 50% at the same computational expense.

NuSTAR detection of 4s Hard X-ray Lags from the Accreting Pulsar GS 0834-430

Directory of Open Access Journals (Sweden)

Bachetti Matteo

2014-01-01

Full Text Available The NuSTAR hard X-ray telescope observed the transient Be/X-ray binary GS 0834–430 during its 2012 outburst. The source is detected between 3 – 79 keV with high statistical significance, and we were able to perform very accurate spectral and timing analysis. The phase-averaged spectrum is consistent with that observed in many other magnetized accreting pulsars. We fail to detect cyclotron resonance scattering features in either phase-averaged nor phase-resolved spectra that would allow us to constrain the pulsar’s magnetic field. We detect a pulse period of ~ 12:29 s in all energy bands. The pulse profile can be modeled with a double Gaussian and shows a strong and smooth hard lag of up to 0.3 cycles in phase, or about 4s between the pulse at ~ 3 and ≳ 30 keV. This is the first report of such a strong lag in high-mass X-ray binary (HMXB pulsars. Previously reported lags have been significantly smaller in phase and restricted to low-energies (E<10 keV. We investigate the possible mechanisms that might produce such lags. We find the most likely explanation for this effect to be a complex beam geometry.

Pulsars as tools for fundamental physics & astrophysics

NARCIS (Netherlands)

Cordes, J.M.; Kramer, M.; Lazio, T.J.W.; Stappers, B.W.; Backer, D.C.; Johnston, S.

2004-01-01

The sheer number of pulsars discovered by the SKA, in combination with the exceptional timing precision it can provide, will revolutionize the field of pulsar astrophysics. The SKA will provide a complete census of pulsars in both the Galaxy and in Galactic globular clusters that can be used to

A SEARCH FOR VERY HIGH ENERGY GAMMA RAYS FROM THE MISSING LINK BINARY PULSAR J1023+0038 WITH VERITAS

Energy Technology Data Exchange (ETDEWEB)

Aliu, E. [Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027 (United States); Archambault, S. [Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada); Archer, A.; Buckley, J. H.; Bugaev, V. [Department of Physics, Washington University, St. Louis, MO 63130 (United States); Benbow, W.; Cerruti, M. [Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States); Bird, R. [School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland); Biteau, J. [Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States); Buchovecky, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Byrum, K. [Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States); Cardenzana, J. V; Dickinson, H. J.; Eisch, J. D. [Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); Chen, X. [Institute of Physics and Astronomy, University of Potsdam, D-14476 Potsdam-Golm (Germany); Ciupik, L. [Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States); Connolly, M. P. [School of Physics, National University of Ireland Galway, University Road, Galway (Ireland); Cui, W.; Feng, Q. [Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907 (United States); Falcone, A., E-mail: ester.aliu.fuste@gmail.com, E-mail: gtrichards@gatech.edu, E-mail: masha.chernyakova@dcu.ie, E-mail: malloryr@gmail.com [Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States); and others

2016-11-10

The binary millisecond radio pulsar PSR J1023+0038 exhibits many characteristics similar to the gamma-ray binary system PSR B1259–63/LS 2883, making it an ideal candidate for the study of high-energy nonthermal emission. It has been the subject of multiwavelength campaigns following the disappearance of the pulsed radio emission in 2013 June, which revealed the appearance of an accretion disk around the neutron star. We present the results of very high energy (VHE) gamma-ray observations carried out by the Very Energetic Radiation Imaging Telescope Array System before and after this change of state. Searches for steady and pulsed emission of both data sets yield no significant gamma-ray signal above 100 GeV, and upper limits are given for both a steady and pulsed gamma-ray flux. These upper limits are used to constrain the magnetic field strength in the shock region of the PSR J1023+0038 system. Assuming that VHE gamma rays are produced via an inverse Compton mechanism in the shock region, we constrain the shock magnetic field to be greater than ∼2 G before the disappearance of the radio pulsar and greater than ∼10 G afterward.

Tokamak

International Nuclear Information System (INIS)

Wesson, John.

1996-01-01

This book is the first compiled collection about tokamak. At first chapter tokamak is represented from fusion point of view and also the necessary conditions for producing power. The following chapters are represent plasma physics, the specifications of tokamak, plasma heating procedures and problems related to it, equilibrium, confinement, magnetohydrodynamic stability, instabilities, plasma material interaction, plasma measurement and experiments regarding to tokamak; an addendum is also given at the end of the book

Dynamic simulations of the cryogenic system of a tokamak

International Nuclear Information System (INIS)

Cirillo, R.; Hoa, C.; Michel, F.; Rousset, B.; Poncet, J.M.

2015-01-01

In a tokamak plasma confinement is achieved through high magnetic fields generated by superconductive coils that need to be cooled down to 4.4 K with a forced flow of supercritical Helium. Tokamak's coil system works cyclically and so it is subject to pulsed heat loads which have to be handled by the refrigerator. This latter has to be sized on the average power value and not according to the peak to limit investment and operation costs and hence the heat load needs to be smoothed. CEA Grenoble is in charge of providing the cryogenic system for the Japanese tokamak JT60-SA, currently under construction in Naka (Japan). Hence, in order to model and study the smoothing strategies, an experimental set up: HELIOS (Helium Loop for high load smoothing) has been built. This is a scaled down model (1:20) of the helium distribution system whose main components are a saturated helium bath and a supercritical helium loop. This large installation can reproduce conditions of pressure, temperature and transport times, similar to those expected in the cooling circuits of the central solenoid superconducting magnets of JT-60SA. The peak loads representative of the tokamak operation have been reproduced and smoothed before they arrive in the refrigerator, by means of a saturated helium bath (thermal reservoir). A dynamic modelling of the cryogenic system is presented, with results on the pulsed load scenarios. All the simulations have been performed with EcosimPro software developed and the cryogenic library: CRYOLIB. This document is made up of an abstract and the slides of the presentation

Overview of the Tokamak de Varennes program

International Nuclear Information System (INIS)

Pacher, H.D.

1986-01-01

The Tokamak de Varennes will be the major Canadian experiment in the magnetic fusion domain. It has a toroidal field of 1.5 tesla, major radius of 0.85 m, a minor radius of 0.25 m, and will study long pulses, up to 30 seconds duration. Initially, a series of successive plasma pulses, each of the order of seconds, will yield a duty factor of over 50 percent. During this phase, the major emphasis will be on the study of impurity generation, transport, and control, plasma-wall interactions and material properties. The program will include studies of fast current rampdown and the resultant current profile modifications. The development of advanced diagnostics will also be undertaken. To attain a higher duty factor with continuous plasma operation, noninductive current drive by radio=frequency will be added as an early upgrade. This will introduce current drive investigations such as transformer recharge and profile relaxation, and enhance the wall and materials study program. In this context, the Tokamak de Varennes will concentrate on the study of impurity exhaust and retention as well as net erosion of the limiter and neutralization plate materials

Detecting pulsars in the Galactic Centre

Science.gov (United States)

Rajwade, K. M.; Lorimer, D. R.; Anderson, L. D.

2017-10-01

Although high-sensitivity surveys have revealed a number of highly dispersed pulsars in the inner Galaxy, none have so far been found in the Galactic Centre (GC) region, which we define to be within a projected distance of 1 pc from Sgr A*. This null result is surprising given that several independent lines of evidence predict a sizable population of neutron stars in the region. Here, we present a detailed analysis of both the canonical and millisecond pulsar populations in the GC and consider free-free absorption and multipath scattering to be the two main sources of flux density mitigation. We demonstrate that the sensitivity limits of previous surveys are not sufficient to detect GC pulsar population, and investigate the optimum observing frequency for future surveys. Depending on the degree of scattering and free-free absorption in the GC, current surveys constrain the size of the potentially observable population (I.e. those beaming towards us) to be up to 52 canonical pulsars and 10 000 millisecond pulsars. We find that the optimum frequency for future surveys is in the range of 9-13 GHz. We also predict that future deeper surveys with the Square Kilometre array will probe a significant portion of the existing radio pulsar population in the GC.

Pulsed Gamma-Rays From PSR J2021 3651 with the Fermi Large Area Telescope

International Nuclear Information System (INIS)

Abdo, Aous A.; Ackermann, M.; Ajello, Marco; Atwood, William B.; Baldini, L.; Ballet, J.; Barbiellini, Guido; Bastieri, Denis; Battelino, Milan; Baughman, B.M.; Bechtol, K.; Bellazzini, Ronaldo; Berenji, Bijan; Bloom, Elliott D.; Bogaert, G.; Borgland, Anders W.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Burnett, Thompson H.

2009-01-01

We report the detection of pulsed gamma-rays from the young, spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The light curve consists of two narrow peaks of similar amplitude separated by 0.468 ± 0.002 in phase. The first peak lags the maximum of the 2 GHz radio pulse by 0.162 ± 0.004 ± 0.01 in phase. The integral gamma-ray photon flux above 100 MeV is (56 ± 3 ± 11) x 10 -8 cm -2 s -1 . The photon spectrum is well-described by an exponentially cut-off power law of the form dF/dE = kE -# Gamma#e (-E/E c ) where the energy E is expressed in GeV. The photon index is Γ = 1.5 ± 0.1 ± 0.1 and the exponential cut-off is E c = 2.4 ± 0.3 ± 0.5 GeV. The first uncertainty is statistical and the second is systematic. The integral photon flux of the bridge is approximately 10% of the pulsed emission, and the upper limit on off-pulse gamma-ray emission from a putative pulsar wind nebula is -2 but a poorly constrained magnetic geometry. Re-analysis of Chandra data enhanced the significance of the weak X-ray pulsations, and the first peak is roughly phase-aligned with the first gamma-ray peak. We discuss the emission region and beaming geometry based on the shape and spectrum of the gamma-ray light curve combined with radio and X-ray measurements, and the implications for the pulsar distance. Gamma-ray emission from the polar cap region seems unlikely for this pulsar.

A search for dispersed radio bursts in archival Parkes Multibeam Pulsar Survey data

OpenAIRE

Bagchi, Manjari; Nieves, Angela Cortes; McLaughlin, Maura

2012-01-01

A number of different classes of potentially extra-terrestrial bursts of radio emission have been observed in surveys with the Parkes 64m radio telescope, including "Rotating Radio Transients", the "Lorimer burst" and "perytons". Rotating Radio Transients are radio pulsars which are best detectable in single-pulse searches. The Lorimer burst is a highly dispersed isolated radio burst with properties suggestive of extragalactic origin. Perytons share the frequency-swept nature of the Rotating ...

The 4U 0115+63: Another energetic gamma ray binary pulsar

Science.gov (United States)

Chadwick, P. M.; Dipper, N. A.; Dowthwaite, J. C.; Kirkman, I. W.; Mccomb, T. J. L.; Orford, K. J.; Turver, K. E.

1985-01-01

Following the discovery of Her X-1 as a source of pulsed 1000 Gev X-rays, a search for emission from an X-ray binary containing a pulsar with similar values of period, period derivative and luminosity was successful. The sporadic X-ray binary 4U 0115-63 has been observed, with probability 2.5 x 10 to the minus 6 power ergs/s to emit 1000 GeV gamma-rays with a time averaged energy flux of 6 to 10 to the 35th power.

Decommissioning the Tokamak Fusion Test Reactor

International Nuclear Information System (INIS)

Spampinato, P.T.; Walton, G.R.

1993-01-01

The Tokamak Fusion Test Reactor (TFTR) at Princeton Plasma Physics Laboratory (PPPL) will complete its experimental lifetime with a series of deuterium-tritium pulses in 1994. As a result, the machine structures will become radioactive, and vacuum components will also be contaminated with tritium. Dose rate levels will range from less than 1 mr/h for external structures to hundreds of mr/h for the vacuum vessel. Hence, decommissioning operations will range from hands on activities to the use of remotely operated equipment. After 21 months of cool down, decontamination and decommissioning (D and D) operations will commence and continue for approximately 15 months. The primary objective is to render the test cell complex re-usable for the next machine, the Tokamak Physics Experiment (TPX). This paper presents an overview of decommissioning TFTR and discusses the D and D objectives

Toward an Empirical Theory of Pulsar Emission. XII. Exploring the Physical Conditions in Millisecond Pulsar Emission Regions

International Nuclear Information System (INIS)

Rankin, Joanna M.; Mitra, Dipanjan; Archibald, Anne; Hessels, Jason; Leeuwen, Joeri van; Ransom, Scott; Stairs, Ingrid; Straten, Willem van; Weisberg, Joel M.

2017-01-01

The five-component profile of the 2.7 ms pulsar J0337+1715 appears to exhibit the best example to date of a core/double-cone emission-beam structure in a millisecond pulsar (MSP). Moreover, three other MSPs, the binary pulsars B1913+16, B1953+29, and J1022+1001, seem to exhibit core/single-cone profiles. These configurations are remarkable and important because it has not been clear whether MSPs and slow pulsars exhibit similar emission-beam configurations, given that they have considerably smaller magnetospheric sizes and magnetic field strengths. MSPs thus provide an extreme context for studying pulsar radio emission. Particle currents along the magnetic polar flux tube connect processes just above the polar cap through the radio-emission region to the light-cylinder and the external environment. In slow pulsars, radio-emission heights are typically about 500 km around where the magnetic field is nearly dipolar, and estimates of the physical conditions there point to radiation below the plasma frequency and emission from charged solitons by the curvature process. We are able to estimate emission heights for the four MSPs and carry out a similar estimation of physical conditions in their much lower emission regions. We find strong evidence that MSPs also radiate by curvature emission from charged solitons.

Toward an Empirical Theory of Pulsar Emission. XII. Exploring the Physical Conditions in Millisecond Pulsar Emission Regions

Energy Technology Data Exchange (ETDEWEB)

Rankin, Joanna M.; Mitra, Dipanjan [Physics Department, University of Vermont, Burlington, VT 05405 (United States); Archibald, Anne; Hessels, Jason; Leeuwen, Joeri van [Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Ransom, Scott [National Radio Astronomy Observatory, Charlottesville, VA 29201 (United States); Stairs, Ingrid [Physics Department, University of British Columbia, V6T 1Z4, BC (Canada); Straten, Willem van [Institute for Radio Astronomy and Space Research, Auckland University of Technology, Auckland 1142 (New Zealand); Weisberg, Joel M., E-mail: Joanna.Rankin@uvm.edu [Physics and Astronomy Department, Carleton College, Northfield, MN 55057 (United States)

2017-08-10

The five-component profile of the 2.7 ms pulsar J0337+1715 appears to exhibit the best example to date of a core/double-cone emission-beam structure in a millisecond pulsar (MSP). Moreover, three other MSPs, the binary pulsars B1913+16, B1953+29, and J1022+1001, seem to exhibit core/single-cone profiles. These configurations are remarkable and important because it has not been clear whether MSPs and slow pulsars exhibit similar emission-beam configurations, given that they have considerably smaller magnetospheric sizes and magnetic field strengths. MSPs thus provide an extreme context for studying pulsar radio emission. Particle currents along the magnetic polar flux tube connect processes just above the polar cap through the radio-emission region to the light-cylinder and the external environment. In slow pulsars, radio-emission heights are typically about 500 km around where the magnetic field is nearly dipolar, and estimates of the physical conditions there point to radiation below the plasma frequency and emission from charged solitons by the curvature process. We are able to estimate emission heights for the four MSPs and carry out a similar estimation of physical conditions in their much lower emission regions. We find strong evidence that MSPs also radiate by curvature emission from charged solitons.

Pulsed Gamma-Rays From PSR J2021 3651 with the Fermi Large Area Telescope

Energy Technology Data Exchange (ETDEWEB)

Abdo, Aous A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Ajello, Marco; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Atwood, William B.; /UC, Santa Cruz; Baldini, L.; /INFN, Pisa; Ballet, J.; /DAPNIA, Saclay; Barbiellini, Guido; /INFN, Trieste /Trieste U.; Bastieri, Denis; /INFN, Padua /Padua U.; Battelino, Milan; /Royal Inst. Tech., Stockholm; Baughman, B.M.; /Ohio State U.; Bechtol, K.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bellazzini, Ronaldo; /INFN, Pisa; Berenji, Bijan; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bloom, Elliott D.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bogaert, G.; /Ecole Polytechnique; Borgland, Anders W.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bregeon, J.; /INFN, Pisa; Brez, A.; /INFN, Pisa; Brigida, M.; /Bari U. /INFN, Bari; Bruel, P.; /Ecole Polytechnique; Burnett, Thompson H.; /Washington U., Seattle /Bari U. /INFN, Bari /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Columbia U. /IASF, Milan /IASF, Milan /DAPNIA, Saclay /INFN, Perugia /Perugia U. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /George Mason U. /Naval Research Lab, Wash., D.C. /IASF, Milan /IASF, Milan /NASA, Goddard /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /INFN, Perugia /Perugia U. /LPCE, Orleans /Montpellier U. /Sonoma State U. /Royal Inst. Tech., Stockholm /Stockholm U. /ASI, Rome /NRAO, Charlottesville /Naval Research Lab, Wash., D.C. /INFN, Trieste /Pavia U. /Bari U. /INFN, Bari /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /UC, Santa Cruz /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /CENBG, Gradignan /CENBG, Gradignan /Manchester U. /Montpellier U. /Bari U. /INFN, Bari; /more authors..

2011-11-30

We report the detection of pulsed gamma-rays from the young, spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The light curve consists of two narrow peaks of similar amplitude separated by 0.468 {+-} 0.002 in phase. The first peak lags the maximum of the 2 GHz radio pulse by 0.162 {+-} 0.004 {+-} 0.01 in phase. The integral gamma-ray photon flux above 100 MeV is (56 {+-} 3 {+-} 11) x 10{sup -8} cm{sup -2} s{sup -1}. The photon spectrum is well-described by an exponentially cut-off power law of the form dF/dE = kE{sup -{Gamma}}e{sup (-E/E{sub c})} where the energy E is expressed in GeV. The photon index is {Gamma} = 1.5 {+-} 0.1 {+-} 0.1 and the exponential cut-off is E{sub c} = 2.4 {+-} 0.3 {+-} 0.5 GeV. The first uncertainty is statistical and the second is systematic. The integral photon flux of the bridge is approximately 10% of the pulsed emission, and the upper limit on off-pulse gamma-ray emission from a putative pulsar wind nebula is < 10% of the pulsed emission at the 95% confidence level. Radio polarization measurements yield a rotation measure of RM = 524 {+-} 4 rad m{sup -2} but a poorly constrained magnetic geometry. Re-analysis of Chandra data enhanced the significance of the weak X-ray pulsations, and the first peak is roughly phase-aligned with the first gamma-ray peak. We discuss the emission region and beaming geometry based on the shape and spectrum of the gamma-ray light curve combined with radio and X-ray measurements, and the implications for the pulsar distance. Gamma-ray emission from the polar cap region seems unlikely for this pulsar.

Fermi Detection of a Luminous gamma-ray Pulsar in a Globular Cluster

Science.gov (United States)

Freire, P. C. C.; Abdo, A. A.; Ajello, M.; Allafort, A.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.;

PULSAR: a balloon-borne experiment to detect variable low energy gamma-ray

International Nuclear Information System (INIS)

Bui-Van, N.A.; Martin, I.M.; Blanco, F.G.; Braga, J.

1983-01-01

The main goal of the balloon-borne 'PULSAR' experiment is to observe γ-ray photons of variable sources and pulsars in the energy range 0.1-5.0 MeV. The geometrical arrangement of the telescope has been designed according to detector sensitivity estimations for the pulsed radiation, which have been made by empirical and analytical methods. From the obtained results we expect to achieve a detection sensitivity of 3.7 x 10 -7 photons cm -2 s -1 KeV -1 (0.1 - 0.5 MeV) and 4.5 x 10 -6 photons cm -2 s -1 KeV -1 (1.0 - 5.0 MeV), for 5 hours integration time at 5 g cm -2 atmospheric depth, with 3σ statistical significance. It was developed an on-board electronics, compatible with the available telemetry capacity, that is able to process the data with a time resolution of approximatelly 4 miliseconds. (Author) [pt

Fermi detection of a luminous γ-ray pulsar in a globular cluster.

Science.gov (United States)

2011-11-25

We report on the Fermi Large Area Telescope's detection of γ-ray (>100 mega-electron volts) pulsations from pulsar J1823-3021A in the globular cluster NGC 6624 with high significance (~7 σ). Its γ-ray luminosity, L(γ) = (8.4 ± 1.6) × 10(34) ergs per second, is the highest observed for any millisecond pulsar (MSP) to date, and it accounts for most of the cluster emission. The nondetection of the cluster in the off-pulse phase implies that it contains <32 γ-ray MSPs, not ~100 as previously estimated. The γ-ray luminosity indicates that the unusually large rate of change of its period is caused by its intrinsic spin-down. This implies that J1823-3021A has the largest magnetic field and is the youngest MSP ever detected and that such anomalous objects might be forming at rates comparable to those of the more normal MSPs.

Fast pulsars, strange stars

International Nuclear Information System (INIS)

Glendenning, N.K.

1990-02-01

The initial motivation for this work was the reported discovery in January 1989 of a 1/2 millisecond pulsar in the remnant of the spectacular supernova, 1987A. The status of this discovery has come into grave doubt as of data taken by the same group in February, 1990. At this time we must consider that the millisecond signal does not belong to the pulsar. The existence of a neutron star in remnant of the supernova is suspected because of recent observations on the light curve of the remnant, and of course by the neutrino burst that announced the supernova. However its frequency is unknown. I can make a strong case that a pulsar rotation period of about 1 ms divides those that can be understood quite comfortably as neutron stars, and those that cannot. What we will soon learn is whether there is an invisible boundary below which pulsar periods do not fall, in which case, all are presumable neutron stars, or whether there exist sub- millisecond pulsars, which almost certainly cannot be neutron stars. Their most plausible structure is that of a self-bound star, a strange-quark-matter star. The existence of such stars would imply that the ground state of the strong interaction is not, as we usually assume, hadronic matter, but rather strange quark matter. Let us look respectively at stars that are bound only by gravity, and hypothetical stars that are self-bound, for which gravity is so to speak, icing on the cake

Pulsar-driven Jets in Supernovae, Gamma-ray Bursts, and SS 433

Science.gov (United States)

Middleditch, John

2010-05-01

The model of pulsar emission through superluminally induced polarization currents (SLIP) predicts that pulsations produced by such currents, induced at many light cylinder radii by a rotating, magnetized body, as would be the case for a neutron star born within any star of more than 1.4 solar masses, will drive pulsations close to the axis of rotation. In SN 1987A, such highly collimated (less than 1 in 10,000) 2.14 ms pulsations, and the similarly collimated jets of particles which they drove, including 1e-6 solar masses with velocities of up to 0.95 c, were responsible for the features of its very early light (days 3 - 20), its "Mystery Spot," observed slightly later (days 30 - 50 and after), and still later, in less collimated form, its bipolarity. SLIP also explains why the 2.14 ms pulsations were more or less consistently observed between years 5.0 and 6.5, and why they eventually disappeared after year 9.0. There is no reason to suggest that this mechanism is not universally applicable to all SNe with gaseous remnants remaining, and thus SN 1987A is the Rosetta Stone for 99% of SNe, gamma-ray bursts, and millisecond pulsars, and possibly SS 433. The axially driven pulsations enforce a toroidal geometry onto all early SNRs, rendering even Ia's unsuitable as standard candles. SLIP predicts that almost all pulsars with very sharp single pulses have been detected because the Earth is in a favored direction where their fluxes diminish only as 1/distance, and this has been verified in the laboratory as well as for the Parkes Multibeam Survey. SLIP also specifically predicts that gamma-ray-burst afterglows will be essentially 100% pulsed at 500 Hz in their proper frame. This work was supported in part by the Department of Energy through the Los Alamos Directed Research Grant DR20080085.

High-beta tokamak research. Annual progress report, 1 August 1982-1 August 1983

International Nuclear Information System (INIS)

Navratil, G.A.

1983-08-01

The main research objectives during the past year fell into four areas: (1) detailed observations over a range of high-beta tokamak equilibria; (2) fabrication of an improved and more flexible high-beta tokamak based on our understanding of the present Torus II; (3) extension of the pulse length to 100 usec with power crowbar operation of the equilibrium field coil sets; and (4) comparison of our equilibrium and stability observations with computational models of MHD equilibrium and stability

Tokamak T-10 multipulse laser scattering: Instrumentation modernization

International Nuclear Information System (INIS)

Baukov, V.A.; Ponomarev, A.V.; Gorshkov, A.V.; Rossikhin, B.A.; Sannikov, V.V.; Grek, B.

1994-01-01

The modernized Thomson scattering diagnostic complex of Tokamak T-10 is described. The complex is based on a high-power neodimium laser. Both the laser fundamental and second harmonics serve to find out the time-dependence of plasma electron temperature and density profiles, as well as to measure the electron distribution function. One detected the scattered laser radiation at θ = 90 degrees and 2.5 degrees angles. The new-version Nd laser generates eight-pulse sequences. The laser radiation energy is E o = 30-50 J/pulse. The radiation divergence was smaller than var-phi = 0.15 mrad. The multiple radiation parameters were found to be very stable. The operator could vary the inter-pulse time intervals within the pulse sequence. The second-harmonic radiation energy was E 2 = 10-15 J/pulse. The data acquisition and analysis system was supported by IBM/AT and Macintosh computers. 6 refs., 1 fig

The galactic distribution of pulsars

International Nuclear Information System (INIS)

Lyne, A.G.

1981-01-01

The galactic distribution of pulsars follows the general form of many population I objects in galactocentric radius, but has a wide distribution above and below the galactic plane due to high space velocities imparted to the pulsars at birth. The evidence for this model is described and the various factors involved in estimating the total galactic population and the galactic birthrate of pulsars are discussed. The various estimates of the galactic population which cluster around 5 x 10 5 are seen to be critically dependent upon the cut-off at low luminosities and upon the value of the mean electron density within 500 pc of the Earth. Estimates of the lifetimes of pulsars are available from both the characteristic ages and proper motion measurements and both give values of about 5 million years. The implied birthrate of one in every 10 years is barely compatible with most estimates of the galactic supernova rate. (Auth.)

High-Cadence Timing Observations of an Exoplanet-Pulsar System, PSR B1257+12

Science.gov (United States)

Rivera, Rudy; Wolszczan, Aleksander; Seymour, Andrew

2016-01-01

The pulsar B1257+12 was regularly observed and timed by Aleksander Wolszczan from its discovery in 1992 up to 2008. It is the first example of an exoplanet-pulsar system, and is modeled to consist of three planets. At the time, long term timing programs lacked the sensitivity to measure effects that low mass, short orbital period bodies would have on the pulse arrival times (TOA's) and its timing residuals. Newer technology, like the PUPPI backend at Arecibo, allows for the exploration of an untouched planet parameter space. The project consisted of conducting precise timing using PUPPI, taking two hour long observations at 327 MHz, 430 MHz, and L-Band Wide (LBW) frequencies for 25 days. The data is processed in order to obtain standard profiles and TOA's that would be introduced into TEMPO2, allowing data point manipulation by fitting them for known pulsar parameters to acquire post fit residuals with expected precisions below 1 μs. The observations yielded residuals ranging between 0.40 μs and 1.89 μs for 430 MHz and 327 MHz, while LBW resulted in values higher than 4.0 μs, which is attributed to the many radio frequency interference (RFI) bands present in the data. Combining the newly and previously acquired data revealed a decrease in the dispersion measure (DM), from 10.16550 pc/cm3 to 10.15325 pc/cm3, since the pulsar was last observed, which allowed a correction for the effects of interstellar scintillation, which are most noticed at 327 MHz.

Timing Noise Analysis of NANOGrav Pulsars

OpenAIRE

Perrodin, Delphine; Jenet, Fredrick; Lommen, Andrea; Finn, Lee; Demorest, Paul; Ferdman, Robert; Gonzalez, Marjorie; Nice, David; Ransom, Scott; Stairs, Ingrid

2013-01-01

We analyze timing noise from five years of Arecibo and Green Bank observations of the seventeen millisecond pulsars of the North-American Nanohertz Observatory for Gravitational Waves (NANOGrav) pulsar timing array. The weighted autocovariance of the timing residuals was computed for each pulsar and compared against two possible models for the underlying noise process. The first model includes red noise and predicts the autocovariance to be a decaying exponential as a function of time lag. Th...

Polarization of the coherent radio emission from pulsars

International Nuclear Information System (INIS)

Ardavan, H.

1982-01-01

The polarization characteristics of the radiation from a quasi-steady pulsar magnetosphere are calculated using the amplitude-modulated-noise interpretation of the data on pulse structures. The total emission consists of three incoherently mixed radiation streams. Two of the independent polarization states are elliptically polarized (modes I and II) and one is linearly polarized (mode III). In the regime where the length scale of the radial distribution of the electric current density is appreciably longer than the wavelength of the radiation, the position angles of modes I and II are orthogonal and those of modes I and III coincident. However, the senses of circular polarization of modes I and II are in general uncorrelated. The degrees of circular polarization of the 'orthogonal' modes are decreasing functions of frequency and both approach zero in the limit where the frequency of the radiation is much higher than the rotation frequency of the pulsar. Longitudinal changes in the position angle and in the sense of circular polarization of each of the elliptically polarized modes are shown to arise, together with mode transitions, in part from the stochastic fluctuations and in part from the systematic variations of the electric current density with the azimuthal angle, in a narrow emitting region adjacent to the light cylinder. (author)

Accretion torques and motion of the hot spot on the accreting millisecond pulsar XTE J1807-294

NARCIS (Netherlands)

Patruno, A.; Hartman, J.M.; Wijnands, R.; Chakrabarty, D.; van der Klis, M.

2010-01-01

We present a coherent timing analysis of the 2003 outburst of the accreting millisecond pulsar (AMXP) XTEJ1807-294. We find a 95% confidence interval for the pulse frequency derivative of (+0.7, +4.7) x 10(-14) Hz s(-1) and (-0.6, +3.8) x 10(-14) Hz s(-1) for the fundamental and second harmonics,

THE PECULIAR PULSAR POPULATION OF THE CENTRAL PARSEC

Energy Technology Data Exchange (ETDEWEB)

Dexter, Jason; O' Leary, Ryan M., E-mail: jdexter@berkeley.edu, E-mail: oleary@berkeley.edu [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States)

2014-03-01

Pulsars orbiting the Galactic center black hole, Sgr A*, would be potential probes of its mass, distance, and spin, and may even be used to test general relativity. Despite predictions of large populations of both ordinary and millisecond pulsars in the Galactic center, none have been detected within 25 pc by deep radio surveys. One explanation has been that hyperstrong temporal scattering prevents pulsar detections, but the recent discovery of radio pulsations from a highly magnetized neutron star (magnetar) within 0.1 pc shows that the temporal scattering is much weaker than predicted. We argue that an intrinsic deficit in the ordinary pulsar population is the most likely reason for the lack of detections to date: a ''missing pulsar problem'' in the Galactic center. In contrast, we show that the discovery of a single magnetar implies efficient magnetar formation in the region. If the massive stars in the central parsec form magnetars rather than ordinary pulsars, their short lifetimes could explain the missing pulsars. Efficient magnetar formation could be caused by strongly magnetized progenitors, or could be further evidence of a top-heavy initial mass function. Furthermore, current high-frequency surveys should already be able to detect bright millisecond pulsars, given the measured degree of temporal scattering.

Plerions and pulsar-powered nebulae

OpenAIRE

Gaensler, Bryan

2000-01-01

In this brief review, I discuss recent developments in the study of pulsar-powered nebulae ("plerions"). The large volume of data which has been acquired in recent years reveals a diverse range of observational properties, demonstrating how differing environmental and pulsar properties manifest themselves in the resulting nebulae.

Pilot pulsar surveys with LOFAR

NARCIS (Netherlands)

Coenen, T.

2013-01-01

We are performing two complementary pilot pulsar surveys as part of LOFAR commissioning. The LOFAR Pilot Pulsar Survey (LPPS) is a shallow all-sky survey using an incoherent combination of LOFAR stations. The LOFAR Tied-Array Survey (LOTAS) is a deeper pilot survey using 19 simultaneous tied-array

Pulsar glitch dynamics

Science.gov (United States)

Morley, P. D.

2018-01-01

We discuss pulsar glitch dynamics from three different viewpoints: statistical description, neutron star equation of state description and finally an electromagnetic field description. For the latter, the pulsar glitch recovery times are the dissipation time constants of sheet surface currents created in response to the glitch-induced crustal magnetic field disruption. We mathematically derive these glitch time constants (Ohmic time constant and Hall sheet current time constant) from a perturbation analysis of the electromagnetic induction equation. Different crustal channels will carry the sheet surface current and their different electron densities determine the time constants.

A Bayesian Classifier for X-Ray Pulsars Recognition

Directory of Open Access Journals (Sweden)

Hao Liang

2016-01-01

Full Text Available Recognition for X-ray pulsars is important for the problem of spacecraft’s attitude determination by X-ray Pulsar Navigation (XPNAV. By using the nonhomogeneous Poisson model of the received photons and the minimum recognition error criterion, a classifier based on the Bayesian theorem is proposed. For X-ray pulsars recognition with unknown Doppler frequency and initial phase, the features of every X-ray pulsar are extracted and the unknown parameters are estimated using the Maximum Likelihood (ML method. Besides that, a method to recognize unknown X-ray pulsars or X-ray disturbances is proposed. Simulation results certificate the validity of the proposed Bayesian classifier.

The high beta tokamak-extended pulse magnetohydrodynamic mode control research program

International Nuclear Information System (INIS)

Maurer, D A; Bialek, J; Byrne, P J; De Bono, B; Levesque, J P; Li, B Q; Mauel, M E; Navratil, G A; Pedersen, T S; Rath, N; Shiraki, D