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Sample records for pulsar xte j1751-305

  1. Discovery of a Second Millisecond Accreting Pulsar: XTE J1751-305

    NASA Astrophysics Data System (ADS)

    Markwardt, C. B.; Swank, J. H.; Strohmayer, T. E.; in 't Zand, J. J. M.; Marshall, F. E.

    2002-08-01

    We report the discovery by the Rossi X-Ray Timing Explorer Proportional Counter Array of a second transient accreting millisecond pulsar, XTE J1751-305, during regular monitoring observations of the Galactic bulge region. The pulsar has a spin frequency of 435 Hz, making it one of the fastest pulsars. The pulsations contain the signature of orbital Doppler modulation, which implies an orbital period of 42 minutes, the shortest orbital period of any known radio or X-ray millisecond pulsar. The mass function, fX=(1.278+/-0.003)×10-6 Msolar, yields a minimum mass for the companion of between 0.013 and 0.017 Msolar, depending on the mass of the neutron star. No eclipses were detected. A previous X-ray outburst in 1998 June was discovered in archival All-Sky Monitor data. Assuming mass transfer in this binary system is driven by gravitational radiation, we constrain the orbital inclination to be in the range 30°-85° and the companion mass to be 0.013-0.035 Msolar. The companion is most likely a heated helium dwarf. We also present results from the Chandra High Resolution Camera-S observations, which provide the best-known position of XTE J1751-305.

  2. Discovery of a Second Millesecond Accreting Pulsar: XTE J1751-305

    NASA Technical Reports Server (NTRS)

    Markwardt, C. B.; Swank, J. H.; Strohmayer, T. E.; intZand, J. J. M.; Marshall, F. E.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We report the discovery by the RXTE PCA of a second transient accreting millisecond pulsar, XTE J1751-305, during regular monitoring observations of the galactic bulge region. The pulsar has a spin frequency of 435 Hz, making it one of the fastest pulsars. The pulsations contain the signature of orbital Doppler modulation, which implies an orbital period of 42 minutes, the shortest orbital period of any known radio or X-ray millisecond pulsar. The mass function, f(sub x) = (1.278 +/- 0.003) x 10 (exp -6) solar mass, yields a minimum mass for the companion of between 0.013 and 0.0017 solar mass depending on the mass of the neutron star. No eclipses were detected. A previous X-ray outburst in June, 1998, was discovered in archival All-Sky Monitor data. Assuming mass transfer in this binary system is driven by gravitational radiation, we constrain the orbital inclination to be in the range 30 deg-85 deg and the companion mass to be 0.013-0.035 solar mass. The companion is most likely a heated helium dwarf. We also present results from the Chandra HRC-S observations which provide the best known position of XTE J1751-305.

  3. Searches for continuous gravitational waves from Scorpius X-1 and XTE J1751-305 in LIGO's sixth science run

    NASA Astrophysics Data System (ADS)

    Meadors, G. D.; Goetz, E.; Riles, K.; Creighton, T.; Robinet, F.

    2017-02-01

    Scorpius X-1 (Sco X-1) and x-ray transient XTE J1751-305 are low-mass x-ray binaries (LMXBs) that may emit continuous gravitational waves detectable in the band of ground-based interferometric observatories. Neutron stars in LMXBs could reach a torque-balance steady-state equilibrium in which angular momentum addition from infalling matter from the binary companion is balanced by angular momentum loss, conceivably due to gravitational-wave emission. Torque balance predicts a scale for detectable gravitational-wave strain based on observed x-ray flux. This paper describes a search for Sco X-1 and XTE J1751-305 in LIGO science run 6 data using the TwoSpect algorithm, based on searching for orbital modulations in the frequency domain. While no detections are claimed, upper limits on continuous gravitational-wave emission from Sco X-1 are obtained, spanning gravitational-wave frequencies from 40 to 2040 Hz and projected semimajor axes from 0.90 to 1.98 light-seconds. These upper limits are injection validated, equal any previous set in initial LIGO data, and extend over a broader parameter range. At optimal strain sensitivity, achieved at 165 Hz, the 95% confidence level random-polarization upper limit on dimensionless strain h0 is approximately 1.8 ×10-24. The closest approach to the torque-balance limit, within a factor of 27, is also at 165 Hz. Upper limits are set in particular narrow frequency bands of interest for J1751-305. These are the first upper limits known to date on r -mode emission from this XTE source. The TwoSpect method will be used in upcoming searches of Advanced LIGO and Virgo data.

  4. Electromagnetic Spindown of a Transient Accreting Millisecond Pulsar During Quiescence

    NASA Astrophysics Data System (ADS)

    Melatos, A.; Mastrano, A.

    2016-02-01

    The measured spindown rates in quiescence of the transient accreting millisecond pulsars IGR J00291+5934, XTE J1751-305, SAX J1808.4-3658, and Swift J1756.9-2508 have been used to estimate the magnetic moments of these objects assuming standard magnetic dipole braking. It is shown that this approach leads to an overestimate if the amount of residual accretion is enough to distort the magnetosphere away from a force-free configuration through magnetospheric mass loading or crushing, so that the lever arm of the braking torque migrates inside the light cylinder. We derive an alternative spindown formula and calculate the residual accretion rates where the formula is applicable. As a demonstration we apply the alternative spindown formula to produce updated magnetic moment estimates for the four objects above. We note that based on current uncertain observations of quiescent accretion rates, magnetospheric mass loading and crushing are neither firmly indicated nor ruled out in these four objects. Because quiescent accretion rates are not measured directly (only upper limits are placed), without more data it is impossible to be confident about whether the thresholds for magnetospheric mass loading or crushing are reached or not.

  5. The optical counterparts of accreting millisecond X-ray pulsars during quiescence

    NASA Astrophysics Data System (ADS)

    D'Avanzo, P.; Campana, S.; Casares, J.; Covino, S.; Israel, G. L.; Stella, L.

    2009-12-01

    Context: Eight accreting millisecond X-ray pulsars (AMXPs) are known to date. Although these systems are well studied at high energies, very little information is available for their optical/NIR counterparts. Up to now, only two of them, SAX J1808.4-3658 and IGR J00291+5934, have a secure multi-band detection of their optical counterparts in quiescence. Aims: All these systems are transient low-mass X-ray binaries. Optical and NIR observations carried out during quiescence give a unique opportunity to constrain the nature of the donor star and to investigate the origin of the observed quiescent luminosity at long wavelengths. In addition, optical observations can be fundamental as they ultimately allow us to estimate the compact object mass through mass function measurements. Methods: Using data obtained with the ESO-Very Large Telescope, we performed a deep optical and NIR photometric study of the fields of XTE J1814-338 and of the ultracompact systems XTE J0929-314 and XTE J1807-294 during quiescence in order to look for the presence of a variable counterpart. If suitable candidates were found, we also carried out optical spectroscopy. Results: We present here the first multi-band (VR) detection of the optical counterpart of XTE J1814-338 in quiescence together with its optical spectrum. The optical light curve shows variability in both bands consistent with a sinusoidal modulation at the known 4.3 h orbital period and presents a puzzling decrease of the V-band flux around superior conjunction that may be interpreted as a partial eclipse. The marginal detection of the very faint counterpart of XTE J0929-314 and deep upper limits for the optical/NIR counterpart of XTE J1807-294 are also reported. We also briefly discuss the results reported in the literature for the optical/NIR counterpart of XTE J1751-305. Conclusions: Our findings are consistent with AMXPs being systems containing an old, weakly magnetized neutron star, reactivated as a millisecond radio pulsar

  6. System mass constraints for the accreting millisecond pulsar XTE J1814-338 using Bowen fluorescence

    NASA Astrophysics Data System (ADS)

    Wang, L.; Steeghs, D.; Casares, J.; Charles, P. A.; Muñoz-Darias, T.; Marsh, T. R.; Hynes, R. I.; O'Brien, K.

    2017-04-01

    We present phase-resolved spectroscopy of the millisecond X-ray pulsar XTE J1814-338 obtained during its 2003 outburst. The spectra are dominated by high-excitation emission lines of He II λ4686, Hβ, and the Bowen blend C III/N III 4630-50 Å. We exploit the proven Bowen fluorescence technique to establish a complete set of dynamical system parameter constraints using bootstrap Doppler tomography, a first for an accreting millisecond X-ray pulsar binary. The reconstructed Doppler map of the N III λ4640 Bowen transition exhibits a statistically significant (>4σ) spot feature at the expected position of the companion star. If this feature is driven by irradiation of the surface of the Roche lobe filling companion, we derive a strict lower limit to the true radial velocity semi-amplitude K2. Combining our donor constraint with the well-constrained orbit of the neutron star leads to a determination of the binary mass ratio: q = 0.123^{+0.012}_{-0.010}. The component masses are not tightly constrained given our lack of knowledge of the binary inclination. We cannot rule out a canonical neutron star mass of 1.4 M⊙ (1.1 M⊙ < M1 < 3.1 M⊙; 95 per cent). The 68/95 per cent confidence limits of M2 are consistent with the companion being a significantly bloated, M-type main-sequence star. Our findings, combined with results from studies of the quiescent optical counterpart of XTE J1814-338, suggest the presence of a rotation-powered millisecond pulsar in XTE J1814-338 during an X-ray quiescent state. The companion mass is typical of the so-called redback pulsar binary systems (M2 ∼ 0.2 M⊙).

  7. The Fading of Transient Anomalous X-Ray Pulsar XTE J1810-197

    NASA Astrophysics Data System (ADS)

    Halpern, J. P.; Gotthelf, E. V.

    2005-01-01

    Three observations of the 5.54 s transient anomalous X-ray pulsar XTE J1810-197 obtained over 6 months with the Newton X-ray Multi-Mirror (XMM-Newton) mission are used to study its spectrum and pulsed light curve as the source fades from outburst. The decay is consistent with an exponential of time constant ~300 days but not a power law as predicted in some models of sudden deep crustal heating events. All spectra are well fitted by a blackbody plus a steep power law, a problematic model that is commonly fitted to anomalous X-ray pulsars (AXPs). A two-temperature blackbody fit is also acceptable and better motivated physically in view of the faint optical/IR fluxes, the X-ray pulse shapes that weakly depend on energy in XTE J1810-197, and the inferred emitting areas that are less than or equal to the surface area of a neutron star. The fitted temperatures remained the same while the flux declined by 46%, which can be interpreted as a decrease in area of the emitting regions. The pulsar continues to spin down, albeit at a reduced rate of (5.1+/-1.6)×10-12 s s-1. The inferred characteristic age τc≡P/2P~17,000 yr, magnetic field strength Bs~1.7×1014 G, and outburst properties are consistent with both the outburst and quiescent X-ray luminosities being powered by magnetic field decay, i.e., XTE J1810-197 is a magnetar.

  8. RXTE and BeppoSAX Observations of the Transient X-ray Pulsar XTE J 18591+083

    NASA Technical Reports Server (NTRS)

    Corbet, R. H. D.; intZand, J. J. M.; Levine, A. M.; Marshall, F. E.

    2008-01-01

    We present observations of the 9.8 s X-ray pulsar XTE J159+083 made with the All-Sky Monitor (ASM) and Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer (RXTE), and the Wide Field Cameras (WFC) on board BeppoSAX. The ASM data cover a 12 year time interval and show that an extended outburst occurred between approximately MJD50, 250, and 50, 460 (1996 June 16 to 1997 January 12). The ASM data excluding this outburst interval suggest a possible 61 day modulation. Eighteen sets of PCA observations were obtained over an approx. one month interval in 1999. The flux variability measured with the PCA appears consistent with the possible period found with the ASM. The PCA measurements of the pulse period showed it to decrease non-monotonically and then to increase significantly. Doppler shifts due to orbital motion rather than accretion torques appear to be better able to explain the pulse period changes. Observations with the WFC during the extended outburst give an error box which is consistent with a previously determined PCA error box but is significantly smaller. The transient nature of XTE J1859+083 and the length of its pulse period are consistent with it being a Be/neutral star binary. The possible 61 day orbital period would be of the expected length for a Be star system with a 9.8 s pulse period.

  9. The Reawakening of the Sleeping X-ray Pulsar XTE J1946+274

    NASA Technical Reports Server (NTRS)

    Mueller, Sebastian; Mueller, Sebastian; Kuechnel, Matthias; Fuerst, Felix; Kreykenbohm, Ingo; Sagredo, Macarena; Obst, Maria; Wilms, Joern; Caballero, Isabel; Potttschmidt, Katja; Ferrigno, Carlo; Rothschild, Richard E.

    2012-01-01

    We report on a series of outbursts of the high mass X-ray binary XTE 11946+274 in 2010/2011 as observed with INTEGRAL, RXTE, and Swift. We discuss possible mechanisms resulting in the extraordinary outburst behavior of this source. The X-ray spectra can be described by standard phenomenological models, enhanced by an absorption feature of unknown origin at about 10 keV and a narrow iron K alpha fluorescence line at 6.4keV, which are variable in flux and pulse phase. We find possible evidence for the presence of a cyclotron resonance scattering feature at about 25 keV at the 93% level. The presence of a strong cyclotron line at 35 keV seen in data from the source's 1998 outburst and confirmed by a reanalysis of these data can be excluded. This result indicates that the cyclotron line feature in XTE 11946+274 is variable between individual outbursts.

  10. Analysis of variability in the burst oscillations of the accreting millisecond pulsar XTE J1814-338

    NASA Technical Reports Server (NTRS)

    Watts, Anna L.; Strohmayer, Tod E.; Markwardt, Craig B.

    2005-01-01

    The accreting millisecond pulsar XTE J1814-338 exhibits oscillations at the known spin frequency during Type I X-ray bursts. The properties of the burst oscillations reflect the nature of the thermal asymmetry on the stellar surface. We present an analysis of the variability of the burst oscillations of this source, focusing on three characteristics: fractional amplitude, harmonic content and frequency. Fractional amplitude and harmonic content constrain the size, shape and position of the emitting region, whilst variations in frequency indicate motion of the emitting region on the neutron star surface. We examine both long-term variability over the course of the outburst, and short-term variability during the bursts. For most of the bursts, fractional amplitude is consistent with that of the accretion pulsations, implying a low degree of fuel spread. There is however a population of bursts whose fractional amplitudes are substantially lower, implying a higher degree of fuel spread, possibly forced by the explosive burning front of a precursor burst. For the first harmonic, substantial differences between the burst and accretion pulsations suggest that hotspot geometry is not the only mechanism giving rise to harmonic content in the latter. Fractional amplitude variability during the bursts is low; we can only rule out the hypothesis that the fractional amplitude remains constant at the l(sigma) level for bursts that do not exhibit photospheric radius expansion (PRE). There are no significant variations in frequency in any of the bursts except for the one burst that exhibits PRE. This burst exhibits a highly significant but small (= 0.1Hz) drop in frequency in the burst rise. The timescale of the frequency shift is slower than simple burning layer expansion models predict, suggesting that other mechanisms may be at work.

  11. THE TRANSIENT ACCRETING X-RAY PULSAR XTE J1946+274: STABILITY OF X-RAY PROPERTIES AT LOW FLUX AND UPDATED ORBITAL SOLUTION

    SciTech Connect

    Marcu-Cheatham, Diana M.; Pottschmidt, Katja; Kühnel, Matthias; Müller, Sebastian; Falkner, Sebastian; Kreykenbohm, Ingo; Caballero, Isabel; Jenke, Peter J.; Wilson-Hodge, Colleen A.; Fürst, Felix; Grinberg, Victoria; Hemphill, Paul B.; Rothschild, Richard E.; Klochkov, Dmitry; Terada, Yukikatsu; and others

    2015-12-10

    We present a timing and spectral analysis of the X-ray pulsar XTE J1946+274 observed with Suzaku during an outburst decline in 2010 October and compare with previous results. XTE J1946+274 is a transient X-ray binary consisting of a Be-type star and a neutron star with a 15.75 s pulse period in a 172 days orbit with 2–3 outbursts per orbit during phases of activity. We improve the orbital solution using data from multiple instruments. The X-ray spectrum can be described by an absorbed Fermi–Dirac cut-off power-law model along with a narrow Fe Kα line at 6.4 keV and a weak Cyclotron Resonance Scattering Feature (CRSF) at ∼35 keV. The Suzaku data are consistent with the previously observed continuum flux versus iron line flux correlation expected from fluorescence emission along the line of sight. However, the observed iron line flux is slightly higher, indicating the possibility of a higher iron abundance or the presence of non-uniform material. We argue that the source most likely has only been observed in the subcritical (non-radiation dominated) state since its pulse profile is stable over all observed luminosities and the energy of the CRSF is approximately the same at the highest (∼5 × 10{sup 37} erg s{sup −1}) and lowest (∼5 × 10{sup 36} erg s{sup −1}) observed 3–60 keV luminosities.

  12. XTE Science Briefing from KSCNF

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The X-ray Timing Explorer (XTE), launched on Dec. 30, 1995, is a Satellite that observes the fast-moving, high-energy worlds of black holes, neutron stars, x-ray pulsars and bursts of X-rays that light up the sky and then disappear forever. This videotape presents a pre-launch science briefing to the press by a few of the scientist and managers associated with the XTE satellite. The moderator for the press briefing is Jim Sahli, from the Public Affairs Office at Goddard Space Flight Center (GSFC). He introduces Alan Bunner, of the High Energy Astrophysics at NASA Headquarters; Fred Lamb, from the University of Illinois; Richard Mashotzky, X Ray Scientist at GSFC; Rick Rothschild, Principal Investigator from the University of California at San Diego; and Dale Schultz, the XTE project manager at GSFC. Dr. Bunner explains the electromagnetic spectrum, the placement of x-rays and the importance of the XTE observations to a better understanding of the Universe. Dr. Lamb, explains the difference between white dwarfs, neutron stars and black holes, and the type of observations that the XTE will give to a further understanding of these phenomena. Dr. Mashotzky expands the viewpoint to beyond the galaxy, and explains the interests of scientists who hope to use XTE to further study Quasars and Active Galactic Nuclei. Dr. Rothschild reviews some of the features of XTE, using a diagram to show the features of interest, such as the X ray Telescopes, and the collecting Proportional Counter Array (PCA.) Mr. Schultz presents a videotape tour of the XTE, in which he shows the scientific instruments and the other features of the satellite. In this tour, the source of each of the instruments is noted. Questions from the members of the press are then fielded. Many of the questions are about the cost of the XTE and any problems that are anticipated in regards to the launch.

  13. Pulsars

    NASA Astrophysics Data System (ADS)

    Stappers, Benjamin W.

    2012-04-01

    Pulsars can be considered as the ultimate time-variable source. They show variations on time-scales ranging from nanoseconds to as long as years, and they emit over almost the entire electromagnetic spectrum. The dominant modulation is associated with the rotation period, which can vary from slighty more than a millisecond to upwards of ten seconds (if we include the magnetars). Variations on time-scales shorter than the pulse period are mostly associated with emission processes and are manifested as giant pulses, microstructure and sub-pulses (to name a few). On time-scales of a rotation to a few hundred rotations are other phenomena also associated with the emission, such as nulling, moding, drifting and intermittency. By probing these and slightly longer time-scales we find that pulsars exhibit ``glitches'', which are rapid variations in spin rates. They are believed to be related to the interaction between the superfluid interior of the neutron star and the outer crust. Detailed studies of glitches can reveal much about the properties of the constituents of neutron stars-the only way to probe the physics of material at such extreme densities. Time-scales of about an hour or longer reveal that some pulsars are in binary systems, in particular the most rapidly rotating systems. Discovering and studying those binary systems provides vital clues to the evolution of massive stars, while some of the systems are also the best probes of strong-field gravity theories; the elusive pulsar-black hole binary would be the ultimate system. Pulsars are tools that allow us to probe a range of phenomena and time-scales. It is possible to measure the time of arrival of pulses from some pulsars to better than a few tens of nanoseconds over years, making them some of the most accurate clocks known. Concerning their rotation, deviations from sphericity may cause pulsars to emit gravitational waves which might then be detected by next-generation gravitational-wave detectors. Pulsars

  14. Hot White Dwarf Donors in Ultracompact X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Bildsten, Lars

    2002-09-01

    The discovery of two accreting millisecond X-ray pulsars in binaries with ~43 minute orbital periods allows for a new probe of the donor's structure. For XTE J1751-305, only a hot white dwarf (WD) can fill the Roche lobe. A cold He WD is a possible solution for XTE J0929-314, although I will show that evolutionary arguments make a hot WD more likely. In addition to being larger than the T=0 models, these finite entropy, low-mass (Mc<0.03 Msolar) WDs have a minimum mass for a fixed core temperature. If they remain hot as they lose mass and expand, they can ``evaporate'' to leave an isolated millisecond radio pulsar. They also adiabatically expand upon mass loss at a rate faster than the growth of the Roche radius if the angular momentum deposited in the disk is not returned to the donor. If the timescale of the resulting runaway mass transfer is shorter than the viscous timescale in the outer disk, then the mass transfer instability of Ruderman & Shaham for He WDs would be realized. However, my estimates of these timescales still make the instability unlikely for adiabatic responses. I close by noting the possible impact of finite temperature WDs on our understanding of AM CVn binaries.

  15. Discovery of a Transient Magnetar: XTE J1810-197

    NASA Technical Reports Server (NTRS)

    Ibrahim, Alaa I.; Markwardt, Craig B.; Swank, Jean H.; Ransom, Scott; Roberts, Mallory; Kaspi, Victoria; Woods, Peter M.; Safi-Harb, Samar; Balman, Solen; Parke, William C.

    2004-01-01

    We report the discovery of a new X-ray pulsar, XTE J1810-197, that was serendipitously discovered on 2003 July 15 by the Rossi X-Ray Timing Explorer (RXTE) while observing the soft gamma repeater SGR 1806-20. The pulsar has a 5.54 s spin period, a soft X-ray spectrum (with a photon index of approx. = 4). and is detectable in earlier RXTE observations back to 2003 January but not before. These show that a transient outburst began between 2002 November 17 and 2003 January 23 and that the source's persistent X-ray flux has been declining since then. The pulsar exhibits a high spin-down rate P approx.= l0(exp -11) s/s with no evidence of Doppler shifts due to a binary companion. The rapid spin-down rate and slow spin period imply a supercritical characteristic magnetic field B approx. = 3 x l0(exp 14) G and a young age tau less than or = 7600 yr. Follow-up Chandra observations provided an accurate position of the source. Within its error radius, the 1.5 m Russian-Turkish Optical Telescope found a limiting magnitude R(sub c) = 21.5. All such properties are strikingly similar to those of anomalous X-ray pulsars ad soft gamma repeaters, providing strong evidence that the source is a new magnetar. However, archival ASCA and ROSAT observations found the source nearly 2 orders of magnitude fainter. This transient behavior and the observed long-term flux variability of the source in absence of an observed SGR-like burst activity make it the first confirmed transient magnetar and suggest that other neutron stars that share the properties of XTE 51810- 197 during its inactive phase may be unidentified transient magnetars awaiting detection via a similar activity. This implies a larger population of magnetars than previously surmised and a possible evolutionary connection between magnetars and other neutron star families. Subject headings: pulsars: general -pulsars: individual (XTE 51810- 197) - stars: magnetic fields -

  16. BeppoSAX observations of XTE J1946+274

    NASA Astrophysics Data System (ADS)

    Doroshenko, R.; Santangelo, A.; Doroshenko, V.; Piraino, S.

    2017-03-01

    We report on the BeppoSAX monitoring of a giant outburst of the transient X-ray pulsar XTE J1946+274 in 1998. The source was detected with a flux of 4 × 10-9 erg cm-2 s-1 (in 0.1-120 keV range). The broadband spectrum, typical for accreting pulsars, is well described by a cutoff power law with a cyclotron resonance scattering feature (CRSF) at 38 keV. This value is consistent with earlier reports based on the observations with Suzaku at factor of ten lower luminosity, which implies that the feature is formed close to the neutron star surface rather than in the accretion column. Pulsations with P 15.82 s were observed up to 70 keV. The pulse profile strongly depends on energy and is characterised by a "soft" and a "hard" peaks shifted by half period, which suggests a strong phase dependence of the spectrum, and that two components with roughly orthogonal beam patterns are responsible for the observed pulse shape. This conclusion is supported by the fact that the CRSF, despite its relatively high energy, is only detected in the spectrum of the soft peak of the pulse profile. Along with the absence of correlation of the line energy with luminosity, this could be explained in the framework of the recently proposed "reflection" model for CRSF formation. However more detailed modelling of both line and continuum formation are required to confirm this interpretation.

  17. Pulsar Animation

    NASA Video Gallery

    Pulsars are thought to emit relatively narrow radio beams, shown as green in this animation. If these beams don't sweep toward Earth, astronomers cannot detect the radio signals. Pulsar gamma-ray e...

  18. Serendipitous Detections of XTE J1906+09 with the Rossi X-ray Timing Explorer

    NASA Technical Reports Server (NTRS)

    Wilson, Colleen A.; Finger, Mark H.; Gogus, Ersin; Woods, Peter M.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    In 1996 during Rossi X-ray Timing Explorer (RXTE) observations of SCR 1900+14, the 89-second X-ray pulsar XTE J1906+09 was discovered. As a result of monitoring campaigns of SGR 1900+14, XTE J1906+09 was also monitored regularly in 1996 September, 1998 May-June, 1998 August-1999 July, and 2000 March-2001 January. A frequency grid search of these observations resulted in detections of only the two previously reported outbursts in 1996 September and 1998 August-September. The non-detection of XTE J1906+09 in most observations indicates that it is a transient X-ray pulsar and therefore likely has a Be star companion, Pulse timing analysis of the second outburst revealed a sinusoidal signature in the pulse frequencies that is likely produced by periastron passage in a long period, eccentric, orbit. During the second outburst, the pulse shape changed with increasing intensity, Low intensity pulse profiles from the second outburst are consistent with profiles from the fainter first outburst. Energy dependent pulse shape variations were seen in both outbursts. Pulse phase spectroscopy was used to quantify these variations. The phase averaged spectrum, using the pulse minimum spectrum as the background spectrum to eliminate effects from SGR 1900+14 and the galactic ridge, was well fitted by an absorbed power law with a high energy cutoff with column density N(sub H) = (6 +/- 1) x 10(exp 22) cm(sup -2), photon index = 1.01 +/- 0.08, cutoff energy E(sub cut) = 11 +/- 1 keV, and folding energy E(sub fold) = 19 +/- 4 keV.

  19. Monitoring The Crab Pulsar

    NASA Technical Reports Server (NTRS)

    Rots, Arnold H.; Swank, Jean (Technical Monitor)

    2001-01-01

    The monitoring of the X-ray pulses from the Crab pulsar is still ongoing at the time of this writing, and we hope to be able to continue the campaign for the life of the XTE mission. We have established beyond all doubt that: (1) the X-ray main pulse leads the radio pulse by approximately 300 microseconds, (2) this phase lag is constant and not influenced by glitches, (3) this lag does not depend on X-ray energy, (4) the relative phase of the two X-ray pulses does not vary, and (5) the spectral indices of primary, secondary, and inter-pulse are distinct and constant. At this time we are investigating whether the radio timing ephemeris can be replaced by an x-ray ephemeris and whether any long-time timing ephemeris can be established. If so, it would enable use to study variations in pulse arrival times at a longer time scales. Such a study is easier in x-rays than at radio wavelengths since the dispersion measure plays no role. These results were reported at the 2000 HEAD Meeting in Honolulu, HI. Travel was paid partly out of this grant. The remainder was applied toward the acquisition of a laptop computer that allows independent and fast analysis of all monitoring observations.

  20. SUBARCSECOND LOCATION OF IGR J17480-2446 WITH ROSSI XTE

    SciTech Connect

    Riggio, A.; Burderi, L.; Egron, E.; Di Salvo, T.; D'Ai, A.; Iaria, R.; Robba, N. R.; Papitto, A.; Belloni, T.; Motta, S.; Floris, M.; Testa, V.; Menna, M. T.

    2012-07-20

    On 2010 October 13, the X-ray astronomical satellite Rossi XTE, during the observation of the newly discovered accretion powered X-ray pulsar IGR J17480-2446, detected a lunar occultation of the source. From knowledge of the lunar topography and Earth, Moon, and spacecraft ephemerides at the epoch of the event, we determined the source position with an accuracy of 40 mas (1{sigma} c.l.), which is interesting, given the very poor imaging capabilities of RXTE ({approx}1 Degree-Sign ). For the first time, using a non-imaging X-ray observatory, the position of an X-ray source with a subarcsecond accuracy is derived, demonstrating the neat capabilities of a technique that can be fruitfully applied to current and future X-ray missions.

  1. Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Beskin, V. S.; Chernov, S. V.; Gwinn, C. R.; Tchekhovskoy, A. A.

    2015-10-01

    Almost 50 years after radio pulsars were discovered in 1967, our understanding of these objects remains incomplete. On the one hand, within a few years it became clear that neutron star rotation gives rise to the extremely stable sequence of radio pulses, that the kinetic energy of rotation provides the reservoir of energy, and that electromagnetic fields are the braking mechanism. On the other hand, no consensus regarding the mechanism of coherent radio emission or the conversion of electromagnetic energy to particle energy yet exists. In this review, we report on three aspects of pulsar structure that have seen recent progress: the self-consistent theory of the magnetosphere of an oblique magnetic rotator; the location, geometry, and optics of radio emission; and evolution of the angle between spin and magnetic axes. These allow us to take the next step in understanding the physical nature of the pulsar activity.

  2. Upper Bounds on r-Mode Amplitudes from Observations of Low-Mass X-Ray Binary Neutron Stars

    NASA Technical Reports Server (NTRS)

    Mahmoodifar, Simin; Strohmayer, Tod

    2013-01-01

    We present upper limits on the amplitude of r-mode oscillations and gravitational-radiation-induced spin-down rates in low-mass X-ray binary neutron stars, under the assumption that the quiescent neutron star luminosity is powered by dissipation from a steady-state r-mode. For masses <2M solar mass we find dimensionless r-mode amplitudes in the range from about 1×10(exp-8) to 1.5×10(exp-6). For the accreting millisecond X-ray pulsar sources with known quiescent spin-down rates, these limits suggest that approx. less than 1% of the observed rate can be due to an unstable r-mode. Interestingly, the source with the highest amplitude limit, NGC 6440, could have an r-mode spin-down rate comparable to the observed, quiescent rate for SAX J1808-3658. Thus, quiescent spin-down measurements for this source would be particularly interesting. For all sources considered here, our amplitude limits suggest that gravitational wave signals are likely too weak for detection with Advanced LIGO. Our highest mass model (2.21M solar mass) can support enhanced, direct Urca neutrino emission in the core and thus can have higher r-mode amplitudes. Indeed, the inferred r-mode spin-down rates at these higher amplitudes are inconsistent with the observed spin-down rates for some of the sources, such as IGR J00291+5934 and XTE J1751-305. In the absence of other significant sources of internal heat, these results could be used to place an upper limit on the masses of these sources if they were made of hadronic matter, or alternatively it could be used to probe the existence of exotic matter in them if their masses were known.

  3. Pulsars Magnetospheres

    NASA Technical Reports Server (NTRS)

    Timokhin, Andrey

    2012-01-01

    Current density determines the plasma flow regime. Cascades are non-stationary. ALWAYS. All flow regimes look different: multiple components (?) Return current regions should have particle accelerating zones in the outer magnetosphere: y-ray pulsars (?) Plasma oscillations in discharges: direct radio emission (?)

  4. Pulsars for the Beginner

    ERIC Educational Resources Information Center

    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)

  5. Accreting Millisecond Pulsars: Neutron Star Masses and Radii

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2004-01-01

    High amplitude X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries. The recent discovery of X-ray burst oscillations from two accreting millisecond pulsars has confirmed this basic picture and provided a new route to measuring neutron star properties and constraining the dense matter equation of state. I will briefly summarize the current observational understanding of accreting millisecond pulsars, and describe recent attempts to determine the mass and radius of the neutron star in XTE J1814-338.

  6. Pulsars - The New Celestial Clocks

    NASA Astrophysics Data System (ADS)

    Backer, D. C.

    Pulsars A Brief History of Neutron Stars Standard Model of Pulsars Origin and Evolution of Isolated Neutron Stars Radio Astronomy Fundamentals Radiation Properties Radio Telescopes Radio Astronomy Receivers Propogation in the Interstellar Medium Search Techniques Pulsar Timing Systems Further Topics on Radio Wave Propagation Absorption Birefringence Scattering Solar Wind and Ionosphere Relativistic Delay in Solar System Potential Pulsar Timing Arrival Time Measurement Time Correction Space Correction Pulsar Parameter Estimation Rotation Noise Astrometry Binary, Millisecond and Globular Cluster Pulsars Origin and Evolution Keplerian Binary Pulsar Timing Relativistic Binary Pulsars Globular Cluster Pulsars Planets Around Pulsars Pulsar Timing Array Time Coordinate Space Coordinate Gravitational Wave Background Pulsar Timing Array Experiments References

  7. Is XTE J1701-407 Extended?

    NASA Astrophysics Data System (ADS)

    Kaplan, David

    2007-09-01

    We recently observed the neutron star X-ray transient XTE J1701-407 with Chandra, using 1 ks of ACIS-S data for localization. However, the Chandra data do not show a point source. Instead the source appears extended over ~6 arcsec. We have investigated the data, consulting with experts both at MIT and SAO, and cannot ascribe the data to purely instrumental effects (aspect errors or pileup). The extended X-ray emission could come from an outflow or a dust scattering halo - both very interesting and rare phenomena. Jets allow detailed calorimetry of the outbursts, while scattering halos lead to geometric distances. We request a 5 ks ACIS-S subarray observation to definitively assess the morphology, trying to discriminate between these scenarios before the target fades into quiescence.

  8. Anomalous Pulsars

    NASA Astrophysics Data System (ADS)

    Malov, I. F.

    Many astrophysicists believe that Anomalous X-Ray Pulsars (AXP), Soft Gamma-Ray Repeaters (SGR), Rotational Radio Transients (RRAT), Compact Central Objects (CCO) and X-Ray Dim Isolated Neutron Stars (XDINS) belong to different classes of anomalous objects with neutron stars as the central bodies inducing all their observable peculiarities. We have shown earlier [1] that AXPs and SGRs could be described by the drift model in the framework of the preposition on usual properties of the central neutron star (rotation periods P 0.01 - 1 sec and, surface magnetic fields B ~ 10^11-10^13 G). Here we shall try to show that some differences of the sources under consideration will be explained by their geometry (particularly, by the angle β between their rotation and magnetic axes). If β <~ 100 (the aligned rotator) the drift waves at the outer layers of the neutron star magnetosphere should play a key role in the observable periodicity. For large values of β (the case of the nearly orthogonal rotator) an accretion from the surrounding medium (for example, from the relic disk) can cause some modulation and transient events in received radiation. Recently Kramer et al. [2] and Camilo et al. [3] have shown that AXPs J1810-197 and 1E 1547.0 - 5408 have both small angles β, that is these sources are nearly aligned rotators, and the drift model should be used for their description. On the other hand, Wang et al. [4] detected IR radiation from the cold disk around the isolated young X-ray pulsar 4U 0142+61. This was the first evidence of the disk-like matter around the neutron star. Probably there is the bimodality of anomalous pulsars. AXPs, SGRs and some radio transients belong to the population of aligned rotators with the angle between the rotation axis and the magnetic moment β < 200. These objects are described by the drift model, and their observed periods are connected with a periodicity of drift waves. Other sources have β ~ 900, and switching on's and switching off

  9. Pulsars and supernova remnants

    SciTech Connect

    Narayan, R.; Schaudt, K.J.

    1988-02-01

    With the recent discovery of the pulsar PSR 1951 + 22 in CTB 80, four pulsars are now known in supernova remnants (SNRs) of the plerion and composite classes. It is argued that this success rate of pulsar detections implies that young fast pulsars have long fan-beams that enable them to be seen from most directions. Based on calculations that use a pulsar luminosity model and allow for selection effects, it is suggested that the best SNRs for future pulsar searches are 3C 58, MSH 11-62, G24.7 + 0.6, and MSH 15-56. It is also concluded that the failure to detect pulsars in shell SNRs implies either that there are no pulsars in these SNRs or that the pulsars are unusually weak, possibly due to slow rotation or weak magnetic fields. 25 references.

  10. Binary and Millisecond Pulsars.

    PubMed

    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.

  11. Delta XTE Lift and Mate at Complex 17A

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This NASA Kennedy Space Center (KSC) video release presents footage of the lift and mate of NASA's X-ray Timing Explorer (XTE) to a McDonnell Douglas Delta II rocket at Launch Complex 17A, Cape Canaveral Air Station. The video includes shots of the workcrews as well as wide angle views of the spacecraft in its launching position. The XTE was launched into a circular orbit with an altitude of 600 km and an inclination of 23 degrees on Dec. 30, 1995.

  12. Ensemble Pulsar Time Scale

    NASA Astrophysics Data System (ADS)

    Yin, D. S.; Gao, Y. P.; Zhao, S. H.

    2016-05-01

    Millisecond pulsars can generate another type of time scale that is totally independent of the atomic time scale, because the physical mechanisms of the pulsar time scale and the atomic time scale are quite different from each other. Usually the pulsar timing observational data are not evenly sampled, and the internals between data points range from several hours to more than half a month. What's more, these data sets are sparse. And all these make it difficult to generate an ensemble pulsar time scale. Hence, a new algorithm to calculate the ensemble pulsar time scale is proposed. Firstly, we use cubic spline interpolation to densify the data set, and make the intervals between data points even. Then, we employ the Vondrak filter to smooth the data set, and get rid of high-frequency noise, finally adopt the weighted average method to generate the ensemble pulsar time scale. The pulsar timing residuals represent clock difference between the pulsar time and atomic time, and the high precision pulsar timing data mean the clock difference measurement between the pulsar time and atomic time with a high signal to noise ratio, which is fundamental to generate pulsar time. We use the latest released NANOGRAV (North American Nanohertz Observatory for Gravitational Waves) 9-year data set to generate the ensemble pulsar time scale. This data set is from the newest NANOGRAV data release, which includes 9-year observational data of 37 millisecond pulsars using the 100-meter Green Bank telescope and 305-meter Arecibo telescope. We find that the algorithm used in this paper can lower the influence caused by noises in timing residuals, and improve long-term stability of pulsar time. Results show that the long-term (> 1 yr) frequency stability of the pulsar time is better than 3.4×10-15.

  13. Binary and Millisecond Pulsars.

    PubMed

    Lorimer, Duncan R

    2005-01-01

    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 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.

  14. Pulsar time scale

    SciTech Connect

    Il'in, V.G.; Llyasov, Yu.P.; Kuz'min, A.D.; Pushkin, S.B.; Palii, G.N.; Shabanova, T.V.; Shchitov, Yu.P.

    1984-05-01

    In this article a new time scale is proposed, that of pulsar time PT which is based on the regular sequence of time intervals between pulses of a pulsar's radio emissions. In discussing variations in the arrival times of pulsar radio emissions, three kinds of variations in the radiation periods are described. PSR 0834 + 06 is used as the basic reference pulsar. Time scales are also determined for reference pulsars PSR 0905 + 08 and 1919 + 21. The initial parameters for the three reference pulsars needed for managing a PT scale are presented. The basic PT scale is defined as the continuous sequence of time intervals between radio-emission pulses of the basic reference pulsar.

  15. Delta XTE Spacecraft Arrives at CCAS Skid Strip

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Footage shows the U.S Air Force Aircraft "Air Mobility Command" approaching, and landing at the Cape Canaveral Air Station Skid Strip (CCAS). The truck carrying the Delta XTE Spacecraft is also shown as it leaves the Air Mobility Command.

  16. Gamma-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2011-01-01

    The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the detection of over 80 gamma-ray pulsars. Several new populations have been discovered, including 24 radio quiet pulsars found through gamma-ray pulsations alone and about 20 millisecond gamma-ray pulsars. The gamma-ray pulsations from millisecond pulsars were discovered by both folding at periods of known radio millisecond pulsars or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -35 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. The higher sensitivity and larger energy range of the Fermi Large Area Telescope has produced detailed energy-dependent light curves and phase-resolved spectroscopy on brighter pulsars, that have ruled out polar cap models as the major source of the emission in favor of outer magnetosphere accelerators. The large number of gamma-ray pulsars now allows for the first time meaningful population and sub-population studies that are revealing surprising properties of these fascinating sources.

  17. Revised Pulsar Spindown

    SciTech Connect

    Contopoulos, Ioannis; Spitkovsky, Anatoly; /KIPAC, Menlo Park

    2005-12-14

    We address the issue of electromagnetic pulsar spindown by combining our experience from the two limiting idealized cases which have been studied in great extent in the past: that of an aligned rotator where ideal MHD conditions apply, and that of a misaligned rotator in vacuum. We construct a spindown formula that takes into account the misalignment of the magnetic and rotation axes, and the magnetospheric particle acceleration gaps. We show that near the death line aligned rotators spin down much slower than orthogonal ones. In order to test this approach, we use a simple Monte Carlo method to simulate the evolution of pulsars and find a good fit to the observed pulsar distribution in the P-{dot P} diagram without invoking magnetic field decay. Our model may also account for individual pulsars spinning down with braking index n < 3, by allowing the corotating part of the magnetosphere to end inside the light cylinder. We discuss the role of magnetic reconnection in determining the pulsar braking index. We show, however, that n {approx} 3 remains a good approximation for the pulsar population as a whole. Moreover, we predict that pulsars near the death line have braking index values n > 3, and that the older pulsar population has preferentially smaller magnetic inclination angles. We discuss possible signatures of such alignment in the existing pulsar data.

  18. Observational properties of pulsars.

    PubMed

    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.

  19. Glitches in southern pulsars

    NASA Astrophysics Data System (ADS)

    Wang, N.; Manchester, R. N.; Pace, R. T.; Bailes, M.; Kaspi, V. M.; Stappers, B. W.; Lyne, A. G.

    2000-10-01

    Timing observations of 40 mostly young pulsars using the ATNF Parkes radio telescope between 1990 January and 1998 December are reported. In total, 20 previously unreported glitches and 10 other glitches were detected in 11 pulsars. These included 12 glitches in PSR J1341-6220, corresponding to a glitch rate of 1.5 glitches per year. We also detected the largest known glitch, in PSR J1614-5047, with Δνgν~6.5×10-6, where ν=1/P is the pulse frequency. Glitch parameters were determined both by extrapolating timing solutions to interglitch intervals and by phase-coherent timing fits across the glitch(es). These fits also give improved positions and dispersion measures for many of the pulsars. Analysis of glitch parameters, both from this work and from previously published results, shows that most glitches have a fractional amplitude Δνgν of between 10-8 and 10-6. There is no consistent relationship between glitch amplitude and the time since the previous glitch or the time to the following glitch, either for the ensemble or for individual pulsars. As previously recognized, the largest glitch activity is seen in pulsars with ages of order 104yr, but for about 30per cent of such pulsars, no glitches were detected in the 8-year data span. There is some evidence for a new type of timing irregularity in which there is a significant increase in pulse frequency over a few days, accompanied by a decrease in the magnitude of the slow-down rate. Fits of an exponential recovery to post-glitch data show that for most older pulsars, only a small fraction of the glitch decays. In some younger pulsars a large fraction of the glitch decays, but in others there is very little decay. Apart from the Crab pulsar, there is no clear dependence of recovery time-scale on pulsar age.

  20. Radio efficiency of pulsars

    SciTech Connect

    Szary, Andrzej; Melikidze, George I.; Gil, Janusz; Zhang, Bing; Xu, Ren-Xin E-mail: zhang@physics.unlv.edu

    2014-03-20

    We investigate radio emission efficiency, ξ, of pulsars and report a near-linear inverse correlation between ξ and the spin-down power, E-dot , as well as a near-linear correlation between ξ and pulsar age, τ. This is a consequence of very weak, if any, dependences of radio luminosity, L, on pulsar period, P, and the period derivative, P-dot , in contrast to X-ray or γ-ray emission luminosities. The analysis of radio fluxes suggests that these correlations are not due to a selection effect, but are intrinsic to the pulsar radio emission physics. We have found that, although with a large variance, the radio luminosity of pulsars is ≈10{sup 29} erg s{sup –1}, regardless of the position in the P-- P-dot diagram. Within such a picture, a model-independent statement can be made that the death line of radio pulsars corresponds to an upper limit in the efficiency of radio emission. If we introduce the maximum value for radio efficiency into the Monte Carlo-based population syntheses we can reproduce the observed sample using the random luminosity model. Using the Kolmogorov-Smirnov test on a synthetic flux distribution reveals a high probability of reproducing the observed distribution. Our results suggest that the plasma responsible for generating radio emission is produced under similar conditions regardless of pulsar age, dipolar magnetic field strength, and spin-down rate. The magnetic fields near the pulsar surface are likely dominated by crust-anchored, magnetic anomalies, which do not significantly differ among pulsars, leading to similar conditions for generating electron-positron pairs necessary to power radio emission.

  1. Stellar evolution and pulsars.

    NASA Technical Reports Server (NTRS)

    Chiu, H.-Y.

    1972-01-01

    It has been found that pulsars are rotating magnetic neutron stars, which are created during catastrophic collapses of old stars whose nuclear fuel has long since been used up. The maximum size of pulsars, based on the fastest rotation period of 33 msec, cannot exceed 100 km. The densest star the theory predicts is the neutron star. Its diameter is only 10 km. The processes producing radiation from pulsars are discussed, giving attention to a process similar to that by which a klystron operates and to a process based on a maser mechanism.

  2. Fermi Pulsar Analysis

    NASA Video Gallery

    This animation illustrates how analysis of Fermi data reveals new pulsars. Fermi's LAT records the precise arrival time and approximate direction of the gamma rays it detects, but to identify a pul...

  3. Wide Band Artificial Pulsar

    NASA Astrophysics Data System (ADS)

    Parsons, Zackary

    2017-01-01

    The Wide Band Artificial Pulsar (WBAP) is an instrument verification device designed and built by the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virgina. The site currently operates the Green Bank Ultimate Pulsar Processing Instrument (GUPPI) and the Versatile Green Bank Astronomical Spectrometer (VEGAS) digital backends for their radio telescopes. The commissioning and continued support for these sophisticated backends has demonstrated a need for a device capable of producing an accurate artificial pulsar signal. The WBAP is designed to provide a very close approximation to an actual pulsar signal. This presentation is intended to provide an overview of the current hardware and software implementations and to also share the current results from testing using the WBAP.

  4. Geriatric Pulsar Still Kicking

    NASA Astrophysics Data System (ADS)

    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

  5. Cosmic Ray Positrons from Pulsars

    NASA Technical Reports Server (NTRS)

    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.

  6. Pulsar statistics and their interpretations

    NASA Technical Reports Server (NTRS)

    Arnett, W. D.; Lerche, I.

    1981-01-01

    It is shown that a lack of knowledge concerning interstellar electron density, the true spatial distribution of pulsars, the radio luminosity source distribution of pulsars, the real ages and real aging rates of pulsars, the beaming factor (and other unknown factors causing the known sample of about 350 pulsars to be incomplete to an unknown degree) is sufficient to cause a minimum uncertainty of a factor of 20 in any attempt to determine pulsar birth or death rates in the Galaxy. It is suggested that this uncertainty must impact on suggestions that the pulsar rates can be used to constrain possible scenarios for neutron star formation and stellar evolution in general.

  7. Pulse Portraiture: Pulsar timing

    NASA Astrophysics Data System (ADS)

    Pennucci, Timothy T.; Demorest, Paul B.; Ransom, Scott M.

    2016-06-01

    Pulse Portraiture is a wideband pulsar timing code written in python. It uses an extension of the FFTFIT algorithm (Taylor 1992) to simultaneously measure a phase (TOA) and dispersion measure (DM). The code includes a Gaussian-component-based portrait modeling routine. The code uses the python interface to the pulsar data analysis package PSRCHIVE (ascl:1105.014) and also requires the non-linear least-squares minimization package lmfit (ascl:1606.014).

  8. A Possible Optical Counterpart to XTE J1550--564

    NASA Astrophysics Data System (ADS)

    Orosz, Jerome; Bailyn, Charles; Jain, Raj

    1998-09-01

    We report YALO consortium observations using the Yale 1m telescope at Cerro Tololo Interamerican Observatory and the ANDICAM CCD camera. We have identified a possible optical counterpart to the recent X-ray transient XTE J1550-564 (IAUC 7008) in V-band images obtained September 8.99 UT. The J2000 coordinates of the candidate are R.A. = 15h51m04s, Decl. = -56o28'37.5", with errors on each value of about +/- 3 arcseconds.

  9. Optical study of pulsars

    NASA Astrophysics Data System (ADS)

    Sanwal, Divas

    The Crab Pulsar emits radiation at all wavelengths from radio to extreme γ-rays including the optical. We have performed extremely high time resolution multicolor photometry of the Crab Pulsar at optical wavelengths to constrain the high energy emission models for pulsars. Our observations with 1 microsecond time resolution are a factor of 20 better than the previous best observations. We have completely resolved the peak of the main pulse of the Crab Pulsar in optical passbands. The peaks of the main pulse and the interpulse move smoothly from the rising branch to the falling branch with neither a flat top nor a cusp. We find that the peak of the Crab Pulsar main pulse in the B band arrives 140 microseconds before the peak of the radio pulse. The color of the emission changes across the phase. The maximum variation in the color ratio is about 25%. The bluest color occurs in the bridge region between the main pulse and the interpulse. The Crab Pulsar has faded by 2 +/- 2.8% since the previous observations in 1991 using the same instrument. The statistics of photon arrival times are consistent with atmospheric scintillation causing most of the variations in addition to the mean pulse variations in the shape. However, the autocorrelation function (ACF) of the Crab Pulsar light curve shows extra correlations at very short time scales. We identify two time scales, one at about 20 microseconds and another one at about 1000 microseconds at which we observe a break in the ACF. We conclude that these short timescale correlations are internal to the pulsar. We attribute the extra correlation observed in our data to microstructures. This is the first time evidence for microstructures has been observed outside the radio wavelengths. The upturn in the ACF at short time scales depends on the color. The U band shows about 10% more correlation at short time scales while the R band shows only about 3% change. We have also observed the young X-ray pulsar PSR 0656+14 at optical

  10. Pulsar lensing geometry

    NASA Astrophysics Data System (ADS)

    Liu, Siqi; Pen, Ue-Li; Macquart, J.-P.; Brisken, Walter; Deller, Adam

    2016-05-01

    We test the inclined sheet pulsar scintillation model (Pen & Levin) against archival very long baseline interferometry (VLBI) data on PSR 0834+06 and show that its scintillation properties can be precisely reproduced by a model in which refraction occurs on two distinct lens planes. These data strongly favour a model in which grazing-incidence refraction instead of diffraction off turbulent structures is the primary source of pulsar scattering. This model can reproduce the parameters of the observed diffractive scintillation with an accuracy at the percent level. Comparison with new VLBI proper motion results in a direct measure of the ionized interstellar medium (ISM) screen transverse velocity. The results are consistent with ISM velocities local to the PSR 0834+06 sight-line (through the Galaxy). The simple 1-D structure of the lenses opens up the possibility of using interstellar lenses as precision probes for pulsar lens mapping, precision transverse motions in the ISM, and new opportunities for removing scattering to improve pulsar timing. We describe the parameters and observables of this double screen system. While relative screen distances can in principle be accurately determined, a global conformal distance degeneracy exists that allows a rescaling of the absolute distance scale. For PSR B0834+06, we present VLBI astrometry results that provide (for the first time) a direct measurement of the distance of the pulsar. For most of the recycled millisecond pulsars that are the targets of precision timing observations, the targets where independent distance measurements are not available. The degeneracy presented in the lens modelling could be broken if the pulsar resides in a binary system.

  11. The Pulsating Pulsar Magnetosphere

    NASA Astrophysics Data System (ADS)

    Tsui, K. H.

    2015-06-01

    Following the basic principles of a charge-separated pulsar magnetosphere, we consider the magnetosphere to be stationary in space, instead of corotating, and the electric field to be uploaded from the potential distribution on the pulsar surface, set up by the unipolar induction. Consequently, the plasma of the magnetosphere undergoes guiding center drifts of the gyromotion due to the forces transverse to the magnetic field. These forces are the electric force, magnetic gradient force, and field line curvature force. Since these plasma velocities are of drift nature, there is no need to introduce an emf along the field lines, which would contradict the {{E}\\parallel }={\\boldsymbol{E}} \\cdot {\\boldsymbol{B}} =0 plasma condition. Furthermore, there is also no need to introduce the critical field line separating the electron and ion open field lines. We present a self-consistent description where the magnetosphere is described in terms of electric and magnetic fields and also in terms of plasma velocities. The fields and velocities are then connected through the space-charge densities self-consistently. We solve the pulsar equation analytically for the fields and construct the standard steady-state pulsar magnetosphere. By considering the unipolar induction inside the pulsar and the magnetosphere outside the pulsar as one coupled system, and under the condition that the unipolar pumping rate exceeds the Poynting flux in the open field lines, plasma pressure can build up in the magnetosphere, in particular, in the closed region. This could cause a periodic opening up of the closed region, leading to a pulsating magnetosphere, which could be an alternative to pulsar beacons. The closed region can also be opened periodically by the build up of toroidal magnetic field through a positive feedback cycle.

  12. Delta XTE Spacecraft Solar Panel Deployment, Hangar AO at Cape Canaveral Air Station

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The footage shows technicians in the clean room checking and adjusting the deployment mechanism of the solar panel for XTE spacecraft. Other scenes show several technicians making adjustments to software for deployment of the solar panels.

  13. NANOGrav Millisecond Pulsar Observing Program

    NASA Astrophysics Data System (ADS)

    Nice, David J.; Nanograv

    2015-01-01

    Gravitational waves from sources such as supermassive black hole binary systems are expected to perturb times-of-flight of signals traveling from pulsars to the Earth. The NANOGrav consortium aims to measure these perturbations in high precision millisecond pulsar timing measurements and thus to directly detect gravitational waves and characterize gravitational wave sources. By observing pulsars over time spans of many years, we are most sensitive to gravitational waves at nanohertz frequencies.In this presentation we describe the NANOGrav observing program. We presently observe an array of 45 millisecond pulsars, evenly divided between the Arecibo Observatory (for pulsars with declinations between -1 and 39 degrees) and the Green Bank Telescope (for other pulsars, with two pulsars overlapping with Arecibo). Observation of a large number of pulsars allows for searches of correlated perturbations between multiple pulsar signals, which will be crucial for achieving high-significance detection of gravitational waves in the face of uncorrelated noise (from gravitational waves and rotation noise) in the individual pulsars. As new high-quality pulsars are discovered, they are added to the program.Observations of each pulsar are made with cadence of 20 to 30 days, with observations of each pulsar in two separate radio bands. Arrival times for nearly all pulsars are measured with precision better than 1 microsecond (averaged over a typical observation of 20 minutes), and in the best cases the precision is better than 100 nanoseconds.We describe the NANOGrav nine-year data release, which contains time-of-arrival measurements and high quality timing solutions from 37 pulsars observed over spans ranging between 0.7 to 9.3 years.

  14. Corrected Coordinates for the Possible OC to XTE J1550-56

    NASA Astrophysics Data System (ADS)

    Orosz, Jerome; Bailyn, Charles; Jain, Raj

    1998-09-01

    There was a slight error in the coordinates of the possible optical counterpart to XTE J1550-56 we reported in our previous telegram. The correct J2000 coordinates are RA = 15:50:58.78, DEC = -56:28:35.0. The coordinates printed on the finding chart available at http://www.astro.psu.edu/users/orosz/xte.html has been corrected (the arrow points to the correct object in any case). We regret this error.

  15. Pulse structure of four pulsars.

    PubMed

    Drake, F D; Craft, H D

    1968-05-17

    The pulse structure of the four known pulsars is given. The pulse is about 38 milliseconds for the two pulsars of longest period, and within the pulsewidth three subpulses typically appear. The pulsar of next longest period typically radiates two pulses separated about 23 milliseconds in time. The one short-period pulsar emits single pulses of constant shape. The first subpulses of all pulsars have nearly the same shape. The shape of the first subpulse agrees well with the pulse shape expected from a radio-emitting sphere which is excited by a spherically expanding disturbance, and in which the radio emission, once excited, decays exponentially.

  16. Pulsars:. Gigantic Nuclei

    NASA Astrophysics Data System (ADS)

    Xu, Renxin

    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.

  17. Modelling pulsar glitches

    NASA Astrophysics Data System (ADS)

    Haskell, Brynmor

    2016-07-01

    Pulsar glitches, i.e. sudden jumps in the spin frequency of pulsars, are thought to be due to the presence of large scale superfluid components in neutron star interiors, and offer a unique insight into the physics of matter at high densities and low temperatures. Nevertheless, more than forty years after the first observation, many open questions still exist on the nature of pulsar glitches. In this talk I will review our current theoretical understanding of glitches, of their trigger mechanisms and of the hydrodynamics of superfluid neutron stars. In particular I will focus on 'superfluid vortex avalanches' and recent advances in applying this paradigm to glitch observations, and I will discuss hydrodynamical modelling of the post-glitch recovery.

  18. Multiwavelength observations of XTE J1859+226

    NASA Astrophysics Data System (ADS)

    Haswell, C. A.; Chaty, S.; Cui, W.; Casares, J. V.; Hynes, R. I.

    2000-03-01

    On March 2 06:00 UT the transient source XTE J1859+226 had faded considerably to R=18.0 in the optical (IAC) and to a flux of about 13 mCrab (RXTE ASM). However, it clearly remains active in the X-rays. From extrapolating the last spectrum obtained with HST on 2000, February 8th we predict the following approximate magnitude and colours: V~18.4, U-B=-0.5, B-V = V-R = R-I = +0.4. A final simultaneous HST/RXTE visit to this source (most likely a black hole) is scheduled for 2000, March 5th between 06:10 and 13:41 UT.

  19. Pulsars and Acceleration Sites

    NASA Technical Reports Server (NTRS)

    Harding, Alice

    2008-01-01

    Rotation-powered pulsars are excellent laboratories for the studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. But even forty years after their discovery, we still do not understand their pulsed emission at any wavelength. I will review both the basic physics of pulsars as well as the latest developments in understanding their high-energy emission. 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 the Gamma-Ray Large Area Space Telescope (GLAST), with launch in May 2008 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.

  20. The Pulsar Search Collaboratory

    ERIC Educational Resources Information Center

    Rosen, R.; Heatherly, S.; McLaughlin, M. A.; Kondratiev, V. I.; Boyles, J. R.; Wilson, M.; Lorimer, D. R.; Lynch, R.; Ransom, S.

    2010-01-01

    The Pulsar Search Collaboratory (PSC) (NSF #0737641) is a joint project between the National Radio Astronomy Observatory and West Virginia University designed to interest high school students in science, technology, engineering, and mathematics related career paths by helping them to conduct authentic scientific research. The 3 year PSC program,…

  1. Nulling and intermittent pulsars

    NASA Astrophysics Data System (ADS)

    Young, Neil

    2011-07-01

    Pulsars are extremely magnetised, rapidly rotating neutron stars which produce beams of electromagnetic radiation that sweep across the Earth. They exhibit a variety of interesting phenomena which allow us to gain insight into the physics of the emission process in these extreme magnetic fields. Intermittent pulsars are instrumental in this study due to their meta-stable configurations which result in abrupt cessation or re-activation of their radio emission. Their behaviour is believed to be tied to transient particle flow in the radio emission region. In the case of PSR B1931+24, the long-term modulation in the radio emission has been linked with the spin-down rate of the pulsar. Thus, offering a unique opportunity to study how magnetospheric changes can affect the magnetic braking of pulsars. Since the discovery of this behaviour in B1931+24, several other sources have been found to show similar radio emission modulation. Results from the analysis of the radio emission behaviour of these sources are presented, along with an update of the work carried out on observations of PSR B1931+24.

  2. Scientific uses of pulsars.

    PubMed

    Counselman, C C; Shapiro, I I

    1968-10-18

    The recently discovered celestial sources of pulsed radio energy can be used to test general relativity, to study the solar corona, and to determine the earth's orbit and ephemeris time. The vector positions and transverse velocities of pulsars can be measured with radio interferometers; in combination with pulse-arrival-time data, the distance determination will yield the average interstellar electron density.

  3. Student Discovers New Pulsar

    NASA Astrophysics Data System (ADS)

    2010-01-01

    A West Virginia high-school student has discovered a new pulsar, using data from the giant Robert C. Byrd Green Bank Telescope (GBT). Shay Bloxton, 15, a participant in a project in which students analyze data from the radio telescope, spotted evidence of the pulsar on October 15. Bloxton, along with NRAO astronomers observed the object again one month later. The new observation confirmed that the object is a pulsar, a rotating, superdense neutron star. Bloxton is a sophomore at Nicholas County High School in Summersville, West Virginia. "I was very excited when I found out I had actually made a discovery," Bloxton said. She went to Green Bank in November to participate in the follow-up observation. She termed that visit "a great experience." "It also helped me learn a lot about how observations with the GBT are actually done," she added. The project in which she participated, called the Pulsar Search Collaboratory (PSC), is a joint project of the National Radio Astronomy Observatory (NRAO) and West Virginia University, funded by a grant from the National Science Foundation. Pulsars are known for their lighthouse-like beams of radio waves that sweep through space as the neutron star rotates, creating a pulse as the beam sweeps by the Earth. First discovered in 1967, pulsars serve as valuable natural "laboratories" for physicists studying exotic states of matter, quantum mechanics and General Relativity. The GBT, dedicated in 2000, has become one of the world's leading tools for discovering and studying pulsars. The PSC, led by NRAO Education Officer Sue Ann Heatherly and Project Director Rachel Rosen, includes training for teachers and student leaders, and provides parcels of data from the GBT to student teams. The project involves teachers and students in helping astronomers analyze data from 1500 hours of observing with the GBT. The 120 terabytes of data were produced by 70,000 individual pointings of the giant, 17-million-pound telescope. Some 300 hours of the

  4. On the randomness of pulsar nulls

    NASA Astrophysics Data System (ADS)

    Redman, Stephen L.; Rankin, Joanna M.

    2009-05-01

    Pulsar nulling is not always a random process; most pulsars, in fact, null non-randomly. The Wald-Wolfowitz statistical runs test is a simple diagnostic that pulsar astronomers can use to identify pulsars that have non-random nulls. It is not clear at this point how the dichotomy in pulsar nulling randomness is related to the underlying nulling phenomenon, but its nature suggests that there are at least two distinct reasons that pulsars null.

  5. The Optimization of GBT Pulsar Data for the GBNCC Pulsar Survey

    NASA Astrophysics Data System (ADS)

    Gordon, Ashlee Nicole; Green Bank NRAO, GBNCC

    2016-01-01

    The Green Bank Telescope collects data from the Green Bank Northern Celestial Cap (GBNCC) pulsar survey in order to find new pulsars within its sensitivity and also, to confirm previously found pulsars within its sensitivity range. The collected data is then loaded into the CyberSKA website database where astronomers are tasked with rating the data sets based on its potential to be a pulsar from 0(unclassified), 1(class 1 pulsar), 2(class 2 pulsar), 3(class 3 pulsar), 4(radio frequency interference), 5(not a pulsar), 6(know pulsar), 7(harmonic of a known pulsar). This specific research done was to use previously classified pulsars to create a python script that will automatically identify the data set as a pulsar or a non-pulsar. After finding the recurring frequencies of radio frequency interference (RFI), the frequencies were then added to a pipeline to further discern pulsars from RFI.

  6. Atomic time scales and pulsars

    NASA Astrophysics Data System (ADS)

    Petit, G.

    2014-12-01

    I review the atomic time scales generated by the BIPM, International Atomic Time TAI and the realization of Terrestrial Time TT(BIPM). TT(BIPM) is shown to be now accurate to within a few 10..16 in relative frequency and the performances of TAI and TT(BIPM) are compared. Millisecond pulsars have a very regular period of rotation and data from several pulsars may be used to realize an ensemble pulsar timescale. It is shown that a pulsar timescale may detect past instabilities in TAI. However TT(BIPM) is much more stable than TAI and should be used as a reference in pulsar analysis. Since the beginning of regular millisecond pulsar observations in the 1980s, primary standards and atomic time have gained one order of magnitude in accuracy every ~ 12 years, and this trend should continue for some time.

  7. Why are Pulsar Planets Rare?

    NASA Astrophysics Data System (ADS)

    Martin, Rebecca G.; Livio, Mario; Palaniswamy, Divya

    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.

  8. The Extended Pulsar Magnetosphere

    NASA Technical Reports Server (NTRS)

    Constantinos, Kalapotharakos; Demosthenes, Kazanas; Ioannis, Contopoulos

    2012-01-01

    We present the structure of the 3D ideal MHD pulsar magnetosphere to a radius ten times that of the light cylinder, a distance about an order of magnitude larger than any previous such numerical treatment. Its overall structure exhibits a stable, smooth, well-defined undulating current sheet which approaches the kinematic split monopole solution of Bogovalov 1999 only after a careful introduction of diffusivity even in the highest resolution simulations. It also exhibits an intriguing spiral region at the crossing of two zero charge surfaces on the current sheet, which shows a destabilizing behavior more prominent in higher resolution simulations. We discuss the possibility that this region is physically (and not numerically) unstable. Finally, we present the spiral pulsar antenna radiation pattern.

  9. Pulsar extinction. [astrophysics

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Baker, K.; Turk, J. S.

    1975-01-01

    Radio emission from pulsars, attributed to an instability associated with the creation of electron-positron pairs from gamma rays was investigated. The condition for pair creation therefore lead to an extinction condition. The relevant physical processes were analyzed in the context of a mathematical model, according to which radiation originated at the polar caps and magnetic field lines changed from a closed configuration to an open configuration at the force balance or corotation radius.

  10. Electrodynamics of Pulsar Magnetospheres

    NASA Astrophysics Data System (ADS)

    Cerutti, Benoît; Beloborodov, Andrei M.

    2016-12-01

    We review electrodynamics of rotating magnetized neutron stars, from the early vacuum model to recent numerical experiments with plasma-filled magnetospheres. Significant progress became possible due to the development of global particle-in-cell simulations which capture particle acceleration, emission of high-energy photons, and electron-positron pair creation. The numerical experiments show from first principles how and where electric gaps form, and promise to explain the observed pulsar activity from radio waves to gamma-rays.

  11. ELECTROMAGNETIC SPINDOWN OF A TRANSIENT ACCRETING MILLISECOND PULSAR DURING QUIESCENCE

    SciTech Connect

    Melatos, A.; Mastrano, A. E-mail: alpham@unimelb.edu.au

    2016-02-10

    The measured spindown rates in quiescence of the transient accreting millisecond pulsars IGR J00291+5934, XTE J1751–305, SAX J1808.4–3658, and Swift J1756.9–2508 have been used to estimate the magnetic moments of these objects assuming standard magnetic dipole braking. It is shown that this approach leads to an overestimate if the amount of residual accretion is enough to distort the magnetosphere away from a force-free configuration through magnetospheric mass loading or crushing, so that the lever arm of the braking torque migrates inside the light cylinder. We derive an alternative spindown formula and calculate the residual accretion rates where the formula is applicable. As a demonstration we apply the alternative spindown formula to produce updated magnetic moment estimates for the four objects above. We note that based on current uncertain observations of quiescent accretion rates, magnetospheric mass loading and crushing are neither firmly indicated nor ruled out in these four objects. Because quiescent accretion rates are not measured directly (only upper limits are placed), without more data it is impossible to be confident about whether the thresholds for magnetospheric mass loading or crushing are reached or not.

  12. The pulsar spectral index distribution

    NASA Astrophysics Data System (ADS)

    Bates, S. D.; Lorimer, D. R.; Verbiest, J. P. W.

    2013-05-01

    The flux-density spectra of radio pulsars are known to be steep and, to first order, described by a power-law relationship of the form Sν ∝ να, where Sν is the flux density at some frequency ν and α is the spectral index. Although measurements of α have been made over the years for several hundred pulsars, a study of the intrinsic distribution of pulsar spectra has not been carried out. From the result of pulsar surveys carried out at three different radio frequencies, we use population synthesis techniques and a likelihood analysis to deduce what underlying spectral index distribution is required to replicate the results of these surveys. We find that in general the results of the surveys can be modelled by a Gaussian distribution of spectral indices with a mean of -1.4 and unit standard deviation. We also consider the impact of the so-called gigahertz-peaked spectrum pulsars proposed by Kijak et al. The fraction of peaked-spectrum sources in the population with any significant turnover at low frequencies appears to be at most 10 per cent. We demonstrate that high-frequency (>2 GHz) surveys preferentially select flatter spectrum pulsars and the converse is true for lower frequency (<1 GHz) surveys. This implies that any correlations between α and other pulsar parameters (for example age or magnetic field) need to carefully account for selection biases in pulsar surveys. We also expect that many known pulsars which have been detected at high frequencies will have shallow, or positive, spectral indices. The majority of pulsars do not have recorded flux density measurements over a wide frequency range, making it impossible to constrain their spectral shapes. We also suggest that such measurements would allow an improved description of any populations of pulsars with `non-standard' spectra. Further refinements to this picture will soon be possible from the results of surveys with the Green Bank Telescope and LOFAR.

  13. Torque Enhancement, Spin Equilibrium, and Jet Power from Disk-Induced Opening of Pulsar Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Parfrey, Kyle; Spitkovsky, Anatoly; Beloborodov, Andrei M.

    2016-05-01

    The interaction of a rotating star’s magnetic field with a surrounding plasma disk lies at the heart of many questions posed by neutron stars in X-ray binaries. We consider the opening of stellar magnetic flux due to differential rotation along field lines coupling the star and disk, using a simple model for the disk-opened flux, the torques exerted on the star by the magnetosphere, and the power extracted by the electromagnetic wind. We examine the conditions under which the system enters an equilibrium spin state, in which the accretion torque is instantaneously balanced by the pulsar wind torque alone. For magnetic moments, spin frequencies, and accretion rates relevant to accreting millisecond pulsars, the spin-down torque from this enhanced pulsar wind can be substantially larger than that predicted by existing models of the disk-magnetosphere interaction, and is in principle capable of maintaining spin equilibrium at frequencies less than 1 kHz. We speculate that this mechanism may account for the non-detection of frequency increases during outbursts of SAX J1808.4-3658 and XTE J1814-338, and may be generally responsible for preventing spin-up to sub-millisecond periods. If the pulsar wind is collimated by the surrounding environment, the resulting jet can satisfy the power requirements of the highly relativistic outflows from Cir X-1 and Sco X-1. In this framework, the jet power scales relatively weakly with accretion rate, {L}{{j}}\\propto {\\dot{M}}4/7, and would be suppressed at high accretion rates only if the stellar magnetic moment is sufficiently low.

  14. Searching for Planets Around Pulsars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-09-01

    Did you know that the very first exoplanets ever confirmed were found around a pulsar? The precise timing measurements of pulsar PSR 1257+12 were what made the discovery of its planetary companions possible. Yet surprisingly, though weve discovered thousands of exoplanets since then, only one other planet has ever been confirmed around a pulsar. Now, a team of CSIRO Astronomy and Space Science researchers are trying to figure out why.Formation ChallengesThe lack of detected pulsar planets may simply reflect the fact that getting a pulsar-planet system is challenging! There are three main pathways:The planet formed before the host star became a pulsar which means it somehow survived its star going supernova (yikes!).The planet formed elsewhere and was captured by the pulsar.The planet formed out of the debris of the supernova explosion.The first two options, if even possible, are likely to be rare occurrences but the third option shows some promise. In this scenario, after the supernova explosion, a small fraction of the material falls back toward the stellar remnant and is recaptured, forming what is known as a supernova fallback disk. According to this model, planets could potentially form out of this disk.Disk ImplicationsLed by Matthew Kerr, the CSIRO astronomers set out to systematically look for these potential planets that might have formed in situ around pulsars. They searched a sample of 151 young, energetic pulsars, scouring seven years of pulse time-of-arrival data for periodic variation that could signal the presence of planetary companions. Their methods to mitigate pulsar timing noise and model realistic orbits allowed them to have good sensitivity to low-mass planets.The results? They found no conclusive evidence that any of these pulsars have planets.This outcome carries with it some significant implications. The pulsar sample spans 2 Myr in age, in which planets should have had enough time to form in debris disks. The fact that none were detected

  15. Pulsar timing and general relativity

    NASA Technical Reports Server (NTRS)

    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.

  16. Magnetars and white dwarf pulsars

    NASA Astrophysics Data System (ADS)

    Lobato, Ronaldo V.; Malheiro, Manuel; Coelho, Jaziel G.

    2016-07-01

    The anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are a class of pulsars understood as neutron stars (NSs) with super strong surface magnetic fields, namely B ≳ 1014G, and for that reason are known as magnetars. However, in the last years, some SGRs/AXPs with low surface magnetic fields B ˜ (1012-1013)G have been detected, challenging the magnetar description. Moreover, some fast and very magnetic white dwarfs (WDs) have also been observed, and at least one showed X-ray energy emission as an ordinary pulsar. Following this fact, an alternative model based on WDs pulsars has been proposed to explain this special class of pulsars. In this model, AXPs and SGRs as dense and magnetized WDs can have surface magnetic field B ˜ 107-1010 G and rotate very fast with frequencies Ω ˜ 1rad/s, consistent with the observed rotation periods P ˜ (2-12)s.

  17. Doppler Imaging of Black Hole SYSTEMS:XTE J1118+480.

    NASA Astrophysics Data System (ADS)

    Callanan, Paul; Perres-Torres, Manuel; Garcia, Michael

    We present time-resolved spectroscopy of the black-hole candidate XTE J1118+480 obtained during its approach to quiescence. Doppler imaging of the intense Hα line shows persistent emission with an origin in the gas stream/hotspot. In addition the Doppler maps show enhanced emission in the +Vx -Vy quadrant clearing incompatible with a stream/hotspot origin. We favour a non-uniform disk intensity distribution due to tidal effects as the origin of this emission. We compare our map with that of XTE J1118+480 in outburst as well as with those of other transient systems in quiescence

  18. Millisecond pulsars: Timekeepers of the cosmos

    NASA Technical Reports Server (NTRS)

    Kaspi, Victoria M.

    1995-01-01

    A brief discussion on the characteristics of pulsars is given followed by a review of millisecond pulsar discoveries including the very first, PRS B1937+21, discovered in 1982. Methods of timing millisecond pulsars and the accuracy of millisecond pulsars as clocks are discussed. Possible reasons for the pulse residuals, or differences between the observed and predicted pulse arrival times for millisecond pulsars, are given.

  19. SEXTANT: A Demonstration of X-ray Pulsar-Based Navigation Using NICER

    NASA Astrophysics Data System (ADS)

    Ray, Paul S.; Mitchell, Jason W; Winternitz, Luke M; Hasouneh, Monther A; Price, Samuel R; Valdez, Jennifer; Yu, Wayne H; Semper, Sean R; Wood, Kent S.; Wolff, Michael Thomas; Arzoumanian, Zaven; Litchford, Ronald J; Gendreau, Keith

    2014-08-01

    The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a technology-demonstration enhancement to the Neutron-star Interior Composition Explorer (NICER) mission. NICER is a NASA Explorer Mission of Opportunity that will be hosted on the International Space Station (ISS). SEXTANT will, for the first time, demonstrate real-time, on-board X-ray pulsar-based navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. The SEXTANT XNAV demonstration will exploit the large collecting area (>1800 cm^2), low background (<0.2 counts/s), and precise timing (<300 ns) of the NICER X-ray Timing Instrument (XTE). Taking advantage of NICER’s science observations of X-ray emitting millisecond pulsars, which are nature’s most stable clocks, the SEXTANT flight software will demonstrate real-time orbit determination with error less than 10 km in any direction, through measurements made over 2 weeks or less in the highly dynamic low-Earth ISS orbit. The completed technology demonstration will bring the XNAV concept and algorithms to a Technology Readiness Level of 8 and will inform the design and configuration of future practical XNAV implementations.

  20. FSSC Science Tools: Pulsar Analysis

    NASA Technical Reports Server (NTRS)

    Thompson, Dave

    2010-01-01

    This slide presentation reviews the typical pulsar analysis, giving tips for screening of the data, the use of time series analysis, and utility tools. Specific information about analyzing Vela data is reviewed.

  1. Fermi's New Pulsar Detection Technique

    NASA Video Gallery

    To locate a pulsar in Fermi LAT data requires knowledge of the object’s sky position, its pulse period, and how the pulse rate slows over time. Computers check many different combinations of posi...

  2. Millisecond radio pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

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

    1989-04-01

    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.

  3. Millisecond radio pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

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

    1989-11-01

    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.

  4. Millisecond radio pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Verbunt, Frank; Lewin, Walter H. G.; Vanparadijs, 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.

  5. The LOFAR Pulsar Data Pipeline

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    The LOw Frequency ARray (LOFAR) for radio astronomy is being built in the Netherlands by ASTRON, with extensions throughout Europe. LOFAR operates at radio frequencies below 250 MHz. The project is an interferometric array of radio antennas grouped into stations that are distributed over an area of hundreds of kilometers. LOFAR will revolutionise low-frequency radio astronomy. Transient radio phenomena and pulsars are one of six LOFAR Key Science Projects (KSPs). As part of the Transients KSP, the Pulsar Working Group has been developing the LOFAR Pulsar Data Pipeline to both study known pulsars as well as search for new ones. The pipeline is being developed for the Blue Gene/P (BG/P) supercomputer and a large Linux cluster in order to utilize enormous amounts of computation capabilities (˜ 50 Tflops) and data streams of up to 23TB/hour. The LOFAR pipeline output will be using the Hierarchical Data Format 5 (HDF5) to efficiently store large amounts of numerical data, and to manage complex data encompassing a variety of data types, across distributed storage and processing architectures. We present the LOFAR Pulsar Data Pipeline overview, the pulsar beam-formed data format, the status of the pipeline processing as well as our future plans for developing additional transient pipelines.

  6. Pulsars In The Headlines

    NASA Astrophysics Data System (ADS)

    Del Puerto, C.

    1967 was the year of the so-called “war of the six days” or “third Arab Israeli war”, the year of the Che Guevara's death in Bolivia, the year of the military coup in Greece and, in medicine, the year of the first human heart transplant. Moreover, the signing of the international agreement on the use of space with peaceful means and the crash of the Russian shuttle Soyuz-1, with Cosmonaut Vladimir Kamarov on board also happened that year. Likewise, Spanish writer and professor of journalists, José Azorín, passed away. However, here we are interested in 1967 because it was the year of the detection of pulsars, which astronomers initially confused with signals from extraterrestrials or Little Green Men. Nowadays, they are still present in the headlines.

  7. Radio pulsar disk electrodynamics

    NASA Technical Reports Server (NTRS)

    Michel, F. C.

    1983-01-01

    Macroscopic physics are discussed for the case of a disk close to an isolated, magnetized, rotating neutron star that acts as a Faraday disk dynamo, while the disk acts as both a load and a neutral sheet. This sheet allows the polar cap current to return to the neutron star, splitting a dipolar field into two monopolar halves. The dominant energy loss is from the stellar wind torque, and the next contribution is dissipation in the auroral zones, where the current returns to the star in a 5 cm-thick sheet. The disk itself may be a source of visible radiation comparable to that in pulsed radio frequency emission. As the pulsar ages, the disk expands and narrows into a ring which, it is suggested, may lead to a cessation of pulsed emission at periods of a few sec.

  8. Millisecond pulsars - Nature's most stable clocks

    NASA Astrophysics Data System (ADS)

    Taylor, Joseph H., Jr.

    1991-07-01

    The author describes the role pulsars might play in time and frequency technology. Millisecond pulsars are rapidly rotating neutron stars: spherical flywheels some 20 km in diameter, 1.4 times as massive as the Sun, and spinning as fast as several thousand radians per second. Radio noise generated in a pulsar's magnetosphere by a highly beamed process is detectable over interstellar distances, as a periodic sequence of pulses similar to the ticks of an excellent clock. High-precision comparisons between pulsar time and terrestrial atomic time show that over intervals of several years, some millisecond pulsars have fractional stabilities comparable to those of the best atomic clocks. The author briefly reviews the physics of pulsars, discusses the techniques of pulsar timing measurements, and summarizes the results of careful studies of pulsar stabilities.

  9. Fermi Finds Youthful Pulsar Among Ancient Stars

    NASA Video Gallery

    In three years, NASA's Fermi has detected more than 100 gamma-ray pulsars, but something new has appeared. Among a type of pulsar with ages typically numbering a billion years or more, Fermi has fo...

  10. Star Cluster Buzzing With Pulsars

    NASA Astrophysics Data System (ADS)

    2005-01-01

    A dense globular star cluster near the center of our Milky Way Galaxy holds a buzzing beehive of rapidly-spinning millisecond pulsars, according to astronomers who discovered 21 new pulsars in the cluster using the National Science Foundation's 100-meter Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. The cluster, called Terzan 5, now holds the record for pulsars, with 24, including three known before the GBT observations. Pulsar Diagram Pulsar Diagram: Click on image for more detail. "We hit the jackpot when we looked at this cluster," said Scott Ransom, an astronomer at the National Radio Astronomy Observatory in Charlottesville, VA. "Not only does this cluster have a lot of pulsars -- and we still expect to find more in it -- but the pulsars in it are very interesting. They include at least 13 in binary systems, two of which are eclipsing, and the four fastest-rotating pulsars known in any globular cluster, with the fastest two rotating nearly 600 times per second, roughly as fast as a household blender," Ransom added. Ransom and his colleagues reported their findings to the American Astronomical Society's meeting in San Diego, CA, and in the online journal Science Express. The star cluster's numerous pulsars are expected to yield a bonanza of new information about not only the pulsars themselves, but also about the dense stellar environment in which they reside and probably even about nuclear physics, according to the scientists. For example, preliminary measurements indicate that two of the pulsars are more massive than some theoretical models would allow. "All these exotic pulsars will keep us busy for years to come," said Jason Hessels, a Ph.D student at McGill University in Montreal. Globular clusters are dense agglomerations of up to millions of stars, all of which formed at about the same time. Pulsars are spinning, superdense neutron stars that whirl "lighthouse beams" of radio waves or light around as they spin. A neutron star is what is

  11. Towards a Realistic Pulsar Magnetosphere

    NASA Technical Reports Server (NTRS)

    Kalapotharakos, Constantinos; Kazanas, Demosthenes; Harding, Alice; Contopoulos, Ioannis

    2012-01-01

    We present the magnetic and electric field structures as well as the currents ami charge densities of pulsar magnetospberes which do not obey the ideal condition, E(raised dot) B = O. Since the acceleration of particles and the production of radiation requires the presence of an electric field component parallel to the magnetic field, E(sub ll) the structure of non-Ideal pulsar magnetospheres is intimately related to the production of pulsar radiation. Therefore, knowledge of the structure of non-Ideal pulsar maglletospheres is important because their comparison (including models for t he production of radiation) with observations will delineate the physics and the parameters underlying the pulsar radiation problem. We implement a variety of prescriptions that support nonzero values for E(sub ll) and explore their effects on the structure of the resulting magnetospheres. We produce families of solutions that span the entire range between the vacuum and the (ideal) Force-Free Electrodynamic solutions. We also compute the amount of dissipation as a fraction of the Poynting flux for pulsars of different angles between the rotation and magnetic axes and conclude that tltis is at most 20-40% (depending on t he non-ideal prescription) in the aligned rotator and 10% in the perpendicular one. We present also the limiting solutions with the property J = pc and discuss their possible implicatioll on the determination of the "on/ off" states of the intermittent pulsars. Finally, we find that solutions with values of J greater than those needed to null E(sub ll) locally produce oscillations, potentially observable in the data.

  12. What brakes the Crab pulsar?

    NASA Astrophysics Data System (ADS)

    Čadež, A.; Zampieri, L.; Barbieri, C.; Calvani, M.; Naletto, G.; Barbieri, M.; Ponikvar, D.

    2016-03-01

    Context. Optical observations provide convincing evidence that the optical phase of the Crab pulsar follows the radio one closely. Since optical data do not depend on dispersion measure variations, they provide a robust and independent confirmation of the radio timing solution. Aims: The aim of this paper is to find a global mathematical description of Crab pulsar's phase as a function of time for the complete set of published Jodrell Bank radio ephemerides (JBE) in the period 1988-2014. Methods: We apply the mathematical techniques developed for analyzing optical observations to the analysis of JBE. We break the whole period into a series of episodes and express the phase of the pulsar in each episode as the sum of two analytical functions. The first function is the best-fitting local braking index law, and the second function represents small residuals from this law with an amplitude of only a few turns, which rapidly relaxes to the local braking index law. Results: From our analysis, we demonstrate that the power law index undergoes "instantaneous" changes at the time of observed jumps in rotational frequency (glitches). We find that the phase evolution of the Crab pulsar is dominated by a series of constant braking law episodes, with the braking index changing abruptly after each episode in the range of values between 2.1 and 2.6. Deviations from such a regular phase description behave as oscillations triggered by glitches and amount to fewer than 40 turns during the above period, in which the pulsar has made more than 2 × 1010 turns. Conclusions: Our analysis does not favor the explanation that glitches are connected to phenomena occurring in the interior of the pulsar. On the contrary, timing irregularities and changes in slow down rate seem to point to electromagnetic interaction of the pulsar with the surrounding environment.

  13. TOWARD A REALISTIC PULSAR MAGNETOSPHERE

    SciTech Connect

    Kalapotharakos, Constantinos; Kazanas, Demosthenes; Harding, Alice

    2012-04-10

    We present the magnetic and electric field structures and the currents and charge densities of pulsar magnetospheres that do not obey the ideal condition, E {center_dot} B = 0. Since the acceleration of particles and the production of radiation require the presence of an electric field component parallel to the magnetic field, E{sub ||}, the structure of non-ideal pulsar magnetospheres is intimately related to the production of pulsar radiation. Therefore, knowledge of the structure of non-ideal pulsar magnetospheres is important because their comparison (including models for the production of radiation) with observations will delineate the physics and the parameters underlying the pulsar radiation problem. We implement a variety of prescriptions that support non-zero values for E{sub ||} and explore their effects on the structure of the resulting magnetospheres. We produce families of solutions that span the entire range between the vacuum and the (ideal) force-free electrodynamic solutions. We also compute the amount of dissipation as a fraction of the Poynting flux for pulsars of different angles between the rotation and magnetic axes and conclude that this is at most 20%-40% (depending on the non-ideal prescription) in the aligned rotator and 10% in the perpendicular one. We present also the limiting solutions with the property J = {rho}c and discuss their possible implication on the determination of the 'on/off' states of the intermittent pulsars. Finally, we find that solutions with values of J greater than those needed to null E{sub ||} locally produce oscillations, potentially observable in the data.

  14. A New Standard Pulsar Magnetosphere

    NASA Technical Reports Server (NTRS)

    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.

  15. A new standard pulsar magnetosphere

    SciTech Connect

    Contopoulos, Ioannis; Kalapotharakos, Constantinos; Kazanas, Demosthenes

    2014-01-20

    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.

  16. Pulsar Timing with the Fermi LAT

    DTIC Science & Technology

    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

  17. PREDICTING RANGES FOR PULSARS' BRAKING INDICES

    SciTech Connect

    Magalhaes, Nadja S.; Miranda, Thaysa A.; Frajuca, Carlos

    2012-08-10

    The theoretical determination of braking indices of pulsars is still an open problem. In this paper we report results of a study concerning such determination based on a modification of the canonical model, which admits that pulsars are rotating magnetic dipoles, and on data from the seven pulsars with known braking indices. In order to test the modified model, we predict ranges for the braking indices of other pulsars.

  18. Search for Millisecond Pulsars for the Pulsar Timing Array project

    NASA Astrophysics Data System (ADS)

    Milia, S.

    2012-03-01

    Pulsars are rapidly rotating highly magnetised neutron stars (i.e. ultra dense stars, where about one solar mass is concentrated in a sphere with a radius of ~ 10 km), which irradiate radio beams in a fashion similar to a lighthouse. As a consequence, whenever the beams cut our line of sight we perceive a radio pulses, one (or two) per pulsar rotation, with a frequency up to hundred of times a second. Owing to their compact nature, rapid spin and high inertia, pulsars are in general fairly stable rotators, hence the Times of Arrival (TOAs) of the pulses at a radio telescope can be used as the ticks of a clock. This holds true in particular for the sub­class of the millisecond pulsars (MSPs), having a spin period smaller than the conventional limit of 30 ms, whose very rapid rotation and relatively older age provide better rotational stability than the ordinary pulsars. Indeed, some MSPs rotate so regularly that they can rival the best atomic clocks on Earth over timespan of few months or years.This feature allows us to use MSPs as tools in a cosmic laboratory, by exploiting a procedure called timing, which consists in the repeated and regular measurement of the TOAs from a pulsar and then in the search for trends in the series of the TOAs over various timespans, from fraction of seconds to decades.For example the study of pulsars in binary systems has already provided the most stringent tests to date of General Relativity in strong gravitational fields and has unambiguously showed the occurrence of the emission of gravitational waves from a binary system comprising two massive bodies in a close orbit. In last decades a new exciting perspective has been opened, i.e. to use pulsars also for a direct detection of the so far elusive gravitational waves and thereby applying the pulsar timing for cosmological studies. In fact, the gravitational waves (GWs) going across our Galaxy pass over all the Galactic pulsars and the Earth, perturbing the space­time at the

  19. The Variability and Spectrum of NGC 4051 from Deep, Simultaneous EUVE and XTE Observations

    NASA Technical Reports Server (NTRS)

    Fruscione, Antonella; Cagnoni, Ilaria; Papadakis, Iossif; McHardy, Ian

    1998-01-01

    We present timing and spectral analysis of the data collected by the Extreme Ultraviolet Explorer Satellite (EUVE) for the Seyfert 1 galaxy NGC 4051 during 1996. NGC 4051 was observed twice in May 1996 and again in December 1996 for a total of more than 200 ksec. The observations were always simultaneous with hard X-ray observations conducted with the X-Ray Timing Explorer (XTE). The EUVE light curves are extremely variable during each observation, with the maximum variability during May 1996 when we registered changes by a factor of 21 over 8 hours and more than a factor of 24 variations from peak to minimum. We detected signal in the EUVE spectrograph in the 75-100 Arange which is well fitted by absorbed power law models. We will illustrate the results of our spectral and detailed power spectrum analysis for the simultaneous EUVE and XTE spectra and light curves and discuss the consequences on possible emission mechanisms.

  20. PINT, a New Pulsar Timing Software

    NASA Astrophysics Data System (ADS)

    Luo, Jing; Jenet, Fredrick A.; Ransom, Scott M.; Demorest, Paul; Van Haasteren, Rutger; Archibald, Anne

    2015-01-01

    We are presenting a new pulsar timing software PINT. The current pulsar timing group are heavily depending on Tempo/Tempo2, a package for analysis pulsar data. However, for a high accuracy pulsar timing related project, such as pulsar timing for gravitational waves, an alternative software is needed for the purpose of examing the results. We are developing a Tempo independent software with a different structure. Different modules is designed to be more isolated and easier to be expanded. Instead of C, we are using Python as our programming language for the advantage of flexibility and powerful docstring. Here, we are presenting the detailed design and the first result of the software.

  1. Gamma Ray Pulsars: Multiwavelength Observations

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2004-01-01

    High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The seven or more pulsars seen by instruments on the Compton Gamma Ray Observatory (CGRO) show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. For all the known gamma-ray pulsars, multiwavelength observations and theoretical models based on such observations offer the prospect of gaining a broad understanding of these rotating neutron stars. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a launch in 2006, will provide a major advance in sensitivity, energy range, and sky coverage.

  2. The Crab pulsar at VHE

    NASA Astrophysics Data System (ADS)

    Zanin, Roberta

    2017-03-01

    The last six years have witnessed major revisions of our knowledge about the Crab Pulsar. The consensus scenario for the origin of the high-energy pulsed emission has been challenged with the discovery of a very-high-energy power law tail extending up to 400 GeV, above the expected spectral cut off at a few GeV. Now, new measurements obtained by the MAGIC collaboration extend the energy spectrum of the Crab Pulsar even further, on the TeV regime. Above 400 GeV the pulsed emission comes mainly from the interpulse, which becomes more prominent with energy due to a harder spectral index. These findings require γ -ray production via inverse Compton scattering close to or beyond the light cylinder radius by an underlying particle population with Lorentz factors greater than 5 × 106. We will present those new results and discuss the implications in our current knowledge concerning pulsar environments.

  3. Formation of Planets around Pulsars

    NASA Astrophysics Data System (ADS)

    Banit, M.; Ruderman, M. A.; Shaham, J.; Applegate, J. H.

    1993-10-01

    Pulse arrival-time delays PSR 1257+ 12 suggest the existence of at least two planets in nearly circular orbits around it. In this paper we discuss different scenarios for the formation of planets in circular orbits around pulsars. Among other topics, we look in some detail at wind emission mechanisms that are particularly relevant to the process of evaporation of planets around pulsars and discuss their possible role in orbit circularization. We conclude that the formation of such planets may occur in a very late phase of low-mass X-ray binary (LMXB) or binary millisecond pulsar (BMP) evolution. Evaporation of the companion star in these phases supplies matter to a circumbinary "excretion" disk in which the physical conditions, similar to those appropriate for the BMP 1957+20 system, may allow the formation of planets like those observed in PSR 1257+12.

  4. Multiwavelength observations of XTE J1859+226 on 1999, November 6th

    NASA Astrophysics Data System (ADS)

    Haswell, C. A.; Chaty, S.; Norton, A. J.; Chen, W.; Hynes, R. I.

    1999-11-01

    Further simultaneous HST and RXTE observations (visit #3) of the new X-ray transient XTE J1859+226 are scheduled for November 6th 1999 19:37 - 22:22 UT. Coordinated multi-wavelength observations (simultaneous, near-simultaneous, and following the evolution over days/weeks) would be extremely helpful. If you can observe simultaneously with HST and/or RXTE, high time-resolution data (< 10 seconds) will be particularly useful.

  5. Radio detection of XTE J1752-223 with the ATCA

    NASA Astrophysics Data System (ADS)

    Brocksopp, Catherine; Corbel, Stephane; Tzioumis, Tasso; Fender, Rob

    2009-11-01

    Following the detection of the new X-ray transient, XTE J1752-223, by RXTE and Swift (ATel. #2258; see also ATels. #2259, #2261, #2263, #2265, #2268, #2269), we have performed radio observations with the Australia Telescope Compact Array and the new CABB back-end. Data were obtained at 5.5 GHz and 9 GHz on October 30 and November 1. We detect a radio source at a position consistent with the X-ray coordinates.

  6. XTE J1752-223: Optical spectroscopy and infrared counterpart detection

    NASA Astrophysics Data System (ADS)

    Torres, M. A. P.; Steeghs, D.; Jonker, P. G.; Thompson, I.; Soderberg, A. M.

    2009-10-01

    Prompted by the discovery of its bright optical counterpart and the announcement of increased X-ray activity (ATels #2258, #2259, #2261, #2265, #2263), we have acquired additional observations of XTE J1752-223 at optical and near-infrared wavelengths. OPTICAL SPECTROSCOPY: An optical spectrum covering 3330-9165 Angstrom was obtained with the MIKE echelle spectrograph on the Magellan Clay telescope starting on 2009 Oct 26 UT 23:52.

  7. Development of the solar array deployment and drive system for the XTE spacecraft

    NASA Technical Reports Server (NTRS)

    Farley, Rodger; Ngo, Son

    1995-01-01

    The X-ray Timing Explorer (XTE) spacecraft is a NASA science low-earth orbit explorer-class satellite to be launched in 1995, and is an in-house Goddard Space Flight Center (GSFC) project. It has two deployable aluminum honeycomb solar array wings with each wing being articulated by a single axis solar array drive assembly. This paper will address the design, the qualification testing, and the development problems as they surfaced of the Solar Array Deployment and Drive System.

  8. Galactic X-ray emission from pulsars

    NASA Technical Reports Server (NTRS)

    Harding, A. K.

    1981-01-01

    The contribution of pulsars to the gamma-ray flux from the galactic plane is examined using data from the most recent pulsar surveys. It is assumed that pulsar gamma-rays are produced by curvature radiation from relativistic particles above the polar cap and attenuated by pair production in the strong magnetic and electric fields. Assuming that all pulsars produce gamma-rays in this way, their luminosities can be predicted as a function of period and magnetic field strength. Using the distribution of pulsars in the galaxy as determined from data on 328 pulsars detected in three surveys, the local gamma-ray production spectrum, the longitude profile, and the latitude profile of pulsar gamma-ray flux are calculated. The largest sources of uncertainty in the size of the pulsar contribution are the value of the mean interstellar electron density, the turnover in the pulsar radio luminosity function, and the average pulsar magnetic field strength. A present estimate is that pulsars contribute from 15 to 20 % of the total flux of gamma-rays from the galactic plane.

  9. Centrifugal Acceleration in Pulsar Magnetospheres

    NASA Astrophysics Data System (ADS)

    Thomas, R. M. C.; Gangadhara, R. T.

    We present a relativistic model of pulsar radio emission by plasma accelerated along the rotating magnetic field lines projected on to a 2D plane perpendicular to the rotation axis. We have derived the expression for the trajectory of a particle, and estimated the spectrum of radio emission by the plasma bunches. We used the parameters given by Peyman &Gangadhara (2002). The analytical expressions for the Stokes parameters are obtained, and their values compared with the observed profiles. The one sense of circular polarization, observed in many pulsars, can be explained in light of our model.

  10. Crustal entrainment and pulsar glitches.

    PubMed

    Chamel, N

    2013-01-04

    Large pulsar frequency glitches are generally interpreted as sudden transfers of angular momentum between the neutron superfluid permeating the inner crust and the rest of the star. Despite the absence of viscous drag, the neutron superfluid is strongly coupled to the crust due to nondissipative entrainment effects. These effects are shown to severely limit the maximum amount of angular momentum that can possibly be transferred during glitches. In particular, it is found that the glitches observed in the Vela pulsar require an additional reservoir of angular momentum.

  11. Sporadically Emitting Pulsars at Low Frequencies

    NASA Astrophysics Data System (ADS)

    Meyers, B. W.; Tremblay, S. E.; Bhat, N. D. R.; Shannon, R. M.

    2017-01-01

    Sporadic emission from pulsars has long been observed, however, the mechanism which causes the intermittency is still a mystery. The proposed observations of three nulling pulsars (J0659+1414, J2048-1616 and J1456-6843), two Rotating Radio Transients (J0410-31 and J1423-56) and one intermittent pulsar (J1107-5907) will provide information on pulsar emission over a variety of time scales. Studying these objects at low frequencies allows us to explore the links between the different populations and how the sporadic emission evolves with frequency. Ultimately, studying these extraordinary pulsars gives us new insight into the dynamic nature of the emission processes and pulsar magnetosphere. This information is imperative for linking models and theories regarding pulsar radio emission physics to the myriad sporadic emission phenomena we observe.

  12. Improving Recent Large-Scale Pulsar Surveys

    NASA Astrophysics Data System (ADS)

    Cardoso, Rogerio Fernando; Ransom, S.

    2011-01-01

    Pulsars are unique in that they act as celestial laboratories for precise tests of gravity and other extreme physics (Kramer 2004). There are approximately 2000 known pulsars today, which is less than ten percent of pulsars in the Milky Way according to theoretical models (Lorimer 2004). Out of these 2000 known pulsars, approximately ten percent are known millisecond pulsars, objects used for their period stability for detailed physics tests and searches for gravitational radiation (Lorimer 2008). As the field and instrumentation progress, pulsar astronomers attempt to overcome observational biases and detect new pulsars, consequently discovering new millisecond pulsars. We attempt to improve large scale pulsar surveys by examining three recent pulsar surveys. The first, the Green Bank Telescope 350MHz Drift Scan, a low frequency isotropic survey of the northern sky, has yielded a large number of candidates that were visually inspected and identified, resulting in over 34.000 thousands candidates viewed, dozens of detections of known pulsars, and the discovery of a new low-flux pulsar, PSRJ1911+22. The second, the PALFA survey, is a high frequency survey of the galactic plane with the Arecibo telescope. We created a processing pipeline for the PALFA survey at the National Radio Astronomy Observatory in Charlottesville- VA, in addition to making needed modifications upon advice from the PALFA consortium. The third survey examined is a new GBT 820MHz survey devoted to find new millisecond pulsars by observing the target-rich environment of unidentified sources in the FERMI LAT catalogue. By approaching these three pulsar surveys at different stages, we seek to improve the success rates of large scale surveys, and hence the possibility for ground-breaking work in both basic physics and astrophysics.

  13. YOUNG RADIO PULSARS IN GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Boyles, J.; Lorimer, D. R.; Turk, P. J.; Mnatsakanov, R.; Lynch, R. S.; Ransom, S. M.; Freire, P. C.; Belczynski, K.

    2011-11-20

    Currently three isolated radio pulsars and one binary radio pulsar with no evidence of any previous recycling are known in 97 surveyed Galactic globular clusters (GCs). As pointed out by Lyne et al., the presence of these pulsars cannot be explained by core-collapse supernovae, as commonly assumed for their counterparts in the Galactic disk. We apply a Bayesian analysis to the results from surveys for radio pulsars in GCs and find the number of potentially observable non-recycled radio pulsars present in all clusters to be <3600. Accounting for beaming and retention considerations, the implied birthrate for any formation scenario for all 97 clusters is <0.25 pulsars century{sup -1} assuming a Maxwellian distribution of velocities with a dispersion of 10 km s{sup -1}. The implied birthrates for higher velocity dispersions are substantially higher than inferred for such pulsars in the Galactic disk. This suggests that the velocity dispersion of young pulsars in GCs is significantly lower than those of disk pulsars. These numbers may be substantial overestimates due to the fact that the currently known sample of young pulsars is observed only in metal-rich clusters. We propose that young pulsars may only be formed in GCs with metallicities with log[Fe/H] > - 0.6. In this case, the potentially observable population of such young pulsars is 447{sup +1420}{sub -399} (the error bars give a 95% confidence interval) and their birthrate is 0.012{sup +0.037}{sub -0.010} pulsars century{sup -1}. The most likely creation scenario to explain these pulsars is the electron capture supernova of an OMgNe white dwarf.

  14. Outburst of the 2 s Anomalous X-ray Pulsar 1E 1547.0-5408

    NASA Technical Reports Server (NTRS)

    Halpern, J. P.; Gotthelf, E. V.; Camilo, F.; Reynolds, J.; Ransom, S. M.

    2008-01-01

    Following our discovery of radio pulsations from the newly recognized anomalous X-ray pulsar (AXP) 1E 1547.0-5408, we initiated X-ray monitoring with the Swift X-ray telescope and obtained a single target-of-opportunity observation with the Newton X-ray Multi-Mirror Mission (XMM-Newton). In comparison with its historic minimum flux of 3 x 10(exp -l3)ergs/sq cm/s, the source was found to be in a record high state, f(sub x)(1-8 keV) = 5 x 10(exp -12)ergs/sq cm/s, or L(sub x) = 1.7 x 10(exp 35)(d/9 kpc )(sup 2)ergs/s, and declining by 25% in 1 month. Extrapolating the decay, we bound the total energy in this outburst to 1042 ergs < E < ergs. The spectra (fitted with a Comptonized blackbody) show that an increase in the temperature and area of a hot region, to 0.5 keV and -16% of the surface area of the neutron star, respectively, are primarily responsible for its increase in luminosity. The energy, spectrum, and timescale of decay are consistent with a deep crustal heating event, similar to an interpretation of the X-ray turn-on of the transient AXP XTE J18 10- 197. Simultaneous with the 4.6 hr ATdA4-Newton observation, we observed at 6.4 GHz with the Parkes telescope, measuring the phase relationship of the radio and X-ray pulse. The X-ray pulsed fraction of 1E 1547.0-5408 is only approx. 7 %, while its radio pulse is relatively broad for such a slow pulsar, which may indicate a nearly aligned rotator. As also inferred from the transient behavior of XTE J18 10-197, the only other AXP known to emit in the radio, the magnetic field rearrangement responsible for this X-ray outburst of 1E 1547.0-5408 is probably the cause of its radio turn-on.

  15. Braking Index of Isolated Pulsars

    NASA Astrophysics Data System (ADS)

    Hamil, Oliver; Stone, Jirina; Urbanec, Martin; Urbancova, Gabriela

    2015-04-01

    Isolated pulsars are rotating neutron stars with accurately measured angular velocities Ω, and their time derivatives which show unambiguously that the pulsars are slowing down. The exact mechanism of the spin-down is a question of debate in detail, but the commonly accepted view is that it arises through emission of magnetic dipole radiation (MDR). The energy loss by a rotating pulsar is proportional to a model dependent power of Ω. This relation leads to the power law Ω˙ = -K Ωn where n is called the braking index, equal to the ratio (ΩΩ̈)/ Ω˙2 . The simple MDR model predicts the value of n = 3, but observations of isolated pulsars provide rather precise values of n, individually accurate to a few percent or better, in the range 1 < n < 2.8, which is consistently less than the predictions of the MDR model. In this work, we study the dynamical limits of the MDR model as a function of angular velocity. The effects of variation in the rest mass, the moment of inertia, and the dependence on a realistic Equation of State of the rotating star are considered. Furthermore, we introduce a simulated superfluid effect by which the angular momentum of the core is eliminated from the calculation.

  16. RESISTIVE SOLUTIONS FOR PULSAR MAGNETOSPHERES

    SciTech Connect

    Li, Jason; Spitkovsky, Anatoly; Tchekhovskoy, Alexander

    2012-02-10

    The current state of the art in the modeling of pulsar magnetospheres invokes either the vacuum or force-free limits for the magnetospheric plasma. Neither of these limits can simultaneously account for both the plasma currents and the accelerating electric fields that are needed to explain the morphology and spectra of high-energy emission from pulsars. To better understand the structure of such magnetospheres, we combine accelerating fields and force-free solutions by considering models of magnetospheres filled with resistive plasma. We formulate Ohm's law in the minimal velocity fluid frame and construct a family of resistive solutions that smoothly bridges the gap between the vacuum and the force-free magnetosphere solutions. The spin-down luminosity, open field line potential drop, and the fraction of open field lines all transition between the vacuum and force-free values as the plasma conductivity varies from zero to infinity. For fixed inclination angle, we find that the spin-down luminosity depends linearly on the open field line potential drop. We consider the implications of our resistive solutions for the spin-down of intermittent pulsars and sub-pulse drift phenomena in radio pulsars.

  17. CHANGES IN THE CRAB PULSAR

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Scientists are learning more about how pulsars work by studying a series of Hubble Space Telescope images of the heart of the Crab Nebula. The images, taken over a period of several months, show that the Crab is a far more dynamic object than previously understood. At the center of the nebula lies the Crab Pulsar. The pulsar is a tiny object by astronomical standards -- only about six miles across -- but has a mass greater than that of the Sun and rotates at a rate of 30 times a second. As the pulsar spins its intense magnetic field whips around, acting like a sling shot, accelerating subatomic particles and sending them hurtling them into space at close to the speed of light. The tiny pulsar and its wind are the powerhouse for the entire Crab Nebula, which is 10 light-years across -- a feat comparable to an object the size of a hydrogen atom illuminating a volume of space a kilometer across. The three pictures shown here, taken from the series of Hubble images, show dramatic changes in the appearance of the central regions of the nebula. These include wisp-like structures that move outward away from the pulsar at half the speed of light, as well as a mysterious 'halo' which remains stationary, but grows brighter then fainter over time. Also seen are the effects of two polar jets that move out along the rotation axis of the pulsar. The most dynamic feature seen -- a small knot that 'dances around' so much that astronomers have been calling it a 'sprite' -- is actually a shock front (where fast-moving material runs into slower-moving material)in one of these polar jets. The telescope captured the images with the Wide Field and Planetary Camera 2 using a filter that passes light of wavelength around 550 nanometers, near the middle of the visible part of the spectrum. The Crab Nebula is located 7,000 light-years away in the constellation Taurus. Credit: Jeff Hester and Paul Scowen (Arizona State University), and NASA

  18. Gamma-Ray Pulsar Studies With GLAST

    SciTech Connect

    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.

  19. Relativistic spin precession in the double pulsar.

    PubMed

    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%.

  20. A Pulsar and a Disk

    NASA Astrophysics Data System (ADS)

    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

  1. Birth of millisecond pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.; Bailyn, C. D.

    1988-01-01

    It is argued here that accretion-induced collapse of white dwarfs in binaries can form millisecond pulsars directly without requiring a precursor low-mass X-ray binary stage. Ablation of the precollapse binary companion by the millisecond pulsar's radiation field, a process invoked to explain some of the characteristics of the recently discovered eclipsing millisecond pulsar, can then yield isolated neutron stars witout requiring an additional stellar encounter.

  2. Spacecraft Navigation Using X-ray Pulsars

    DTIC Science & Technology

    2006-01-01

    make them attractive as potential natural naviga- tion beacons and why a practical implementation looks most feasible in the X-ray band. We then...describe the history of the X-ray navigation program at NRL up through our current Defense Advanced Research Proj- ects Agency (DARPA) program. Finally, we...that produce the powerful radiation beams. These pulsars then turn off and inhabit the “pulsar graveyard.” During their lives, these pulsars make very

  3. Self-modulational formation of pulsar microstructures

    NASA Technical Reports Server (NTRS)

    Chian, A. C.-L.; Kennel, C. F.

    1987-01-01

    A nonlinear plasma theory for self modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron positron plasma. The nonlinearities arising from wave intensity induced particle mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

  4. Moving relativistic large-scale X-ray jets in the microquasar XTE J1550-564

    NASA Astrophysics Data System (ADS)

    Corbel, S.; Fender, R. P.; Tzioumis, A. K.; Tomsick, J. A.; Orosz, J. A.; Miller, J. M.; Wijnands, R.; Kaaret, P.

    2003-10-01

    We have discovered large-scale moving X-ray and radio jets from the microquasar XTE J1550-564. Using X-ray and radio observations performed between 2000 and 2002, we showed that plasma ejected from XTE J1550-564 has been able to travel at relativistic velocities during many years, with evidence for gradual deceleration. The broadband spectrum of the jets is consistent with synchrotron emission from high energy particles accelerated in shocks. Full details can be found in Corbel et al. [Science 298 (2002a) 196], Karret et al. [ApJ 582 (2003) 933] and Tomsick et al. [ApJ (2003) 945].

  5. Moving relativistic large-scale X-ray jets in the microquasar XTE J1550-564

    NASA Astrophysics Data System (ADS)

    Corbel, S.; Fender, R. P.; Tzioumis, A. K.; Tomsick, J. A.; Orosz, J. A.; Miller, J. M.; Wijnands, R.; Kaaret, P.

    We have discovered large-scale moving X-ray and radio jets from the microquasar XTE J1550-564. Using X-ray observations from the Chandra Observatory performed between June 2000 (see also Tomsick et al., these proceedings) and June 2002, we showed that ejected plasma from XTE J1550-564 has been able to travel at relativistic velocities during many years, with evidence for gradual deceleration. The broadband spectrum of the jets is consistent with synchrotron emission from high energy particles accelerated in shocks. Full details can be found in Corbel et al. 2002, Kaaret et al. 2002, Tomsick et al. 2002.

  6. The spin evolution of young pulsars

    NASA Astrophysics Data System (ADS)

    Espinoza, Cristóbal M.

    2013-03-01

    The current understanding of the spin evolution of young pulsars is reviewed through a compilation of braking index measurements. An immediate conclusion is that the spin evolution of all pulsars with a measured braking index is not purely caused by a constant magnetic dipole. The case of PSR J1734-3333 and its upward movement towards the magnetars is used as a guide to try to understand why pulsars evolve with n < 3. Evolution between different pulsar families, driven by the emergence of a hidden internal magnetic field, appears as one possible picture.

  7. Pulsar discovery by global volunteer computing.

    PubMed

    Knispel, B; Allen, B; Cordes, J M; Deneva, J S; Anderson, D; Aulbert, C; Bhat, N D R; Bock, O; Bogdanov, S; Brazier, A; Camilo, F; Champion, D J; Chatterjee, S; Crawford, F; Demorest, P B; Fehrmann, H; Freire, P C C; Gonzalez, M E; Hammer, D; Hessels, J W T; Jenet, F A; Kasian, L; Kaspi, V M; Kramer, M; Lazarus, P; van Leeuwen, J; Lorimer, D R; Lyne, A G; Machenschalk, B; McLaughlin, M A; Messenger, C; Nice, D J; Papa, M A; Pletsch, H J; Prix, R; Ransom, S M; Siemens, X; Stairs, I H; Stappers, B W; Stovall, K; Venkataraman, A

    2010-09-10

    Einstein@Home aggregates the computer power of hundreds of thousands of volunteers from 192 countries to mine large data sets. It has now found a 40.8-hertz isolated pulsar in radio survey data from the Arecibo Observatory taken in February 2007. Additional timing observations indicate that this pulsar is likely a disrupted recycled pulsar. PSR J2007+2722's pulse profile is remarkably wide with emission over almost the entire spin period; the pulsar likely has closely aligned magnetic and spin axes. The massive computing power provided by volunteers should enable many more such discoveries.

  8. ON PULSAR DISTANCE MEASUREMENTS AND THEIR UNCERTAINTIES

    SciTech Connect

    Verbiest, J. P. W.; Lee, K. J.; Weisberg, J. M.; Chael, A. A.; Lorimer, D. R.

    2012-08-10

    Accurate distances to pulsars can be used for a variety of studies of the Galaxy and its electron content. However, most distance measures to pulsars have been derived from the absorption (or lack thereof) of pulsar emission by Galactic H I gas, which typically implies that only upper or lower limits on the pulsar distance are available. We present a critical analysis of all measured H I distance limits to pulsars and other neutron stars, and translate these limits into actual distance estimates through a likelihood analysis that simultaneously corrects for statistical biases. We also apply this analysis to parallax measurements of pulsars in order to obtain accurate distance estimates and find that the parallax and H I distance measurements are biased in different ways, because of differences in the sampled populations. Parallax measurements typically underestimate a pulsar's distance because of the limited distance to which this technique works and the consequential strong effect of the Galactic pulsar distribution (i.e., the original Lutz-Kelker bias), in H I distance limits, however, the luminosity bias dominates the Lutz-Kelker effect, leading to overestimated distances because the bright pulsars on which this technique is applicable are more likely to be nearby given their brightness.

  9. The pulsar planet production process

    NASA Technical Reports Server (NTRS)

    Phinney, E. S.; Hansen, B. M. S.

    1993-01-01

    Most plausible scenarios for the formation of planets around pulsars end with a disk of gas around the pulsar. The supplicant author then points to the solar system to bolster faith in the miraculous transfiguration of gas into planets. We here investigate this process of transfiguration. We derive analytic sequences of quasi-static disks which give good approximations to exact solutions of the disk diffusion equation with realistic opacity tables. These allow quick and efficient surveys of parameter space. We discuss the outward transfer of mass in accretion disks and the resulting timescale constraints, the effects of illumination by the central source on the disk and dust within it, and the effects of the widely different elemental compositions of the disks in the various scenarios, and their extensions to globular clusters. We point out where significant uncertainties exist in the appropriate grain opacities, and in the effect of illumination and winds from the neutron star.

  10. Pair-Starved Pulsar Magnetospheres

    NASA Technical Reports Server (NTRS)

    Muslimov, Alex G.; Harding, Alice K.

    2009-01-01

    We propose a simple analytic model for the innermost (within the light cylinder of canonical radius, approx. c/Omega) structure of open-magnetic-field lines of a rotating neutron star (NS) with relativistic outflow of charged particles (electrons/positrons) and arbitrary angle between the NS spin and magnetic axes. We present the self-consistent solution of Maxwell's equations for the magnetic field and electric current in the pair-starved regime where the density of electron-positron plasma generated above the pulsar polar cap is not sufficient to completely screen the accelerating electric field and thus establish thee E . B = 0 condition above the pair-formation front up to the very high altitudes within the light cylinder. The proposed mode1 may provide a theoretical framework for developing the refined model of the global pair-starved pulsar magnetosphere.

  11. Black Hole Candidate XTE J1859+226 in the Low/Hard State

    NASA Astrophysics Data System (ADS)

    Miller, J. M.; Fox, D. W.; Pooley, D.; Lewin, W. H. G.

    2000-07-01

    Recent flaring activity of this source in the optical (Casares et al. 2000, IAUC #7451) has motivated a public RXTE TOO observation on 8 July 2000. XTE J1859+226 is a known X-ray nova that reached 1.4 Crab in the RXTE/ASM in October 1999 (Smith 1999, ATEL #47). During that outburst the source exhibited 150 and 187 Hz quasi-periodic oscillations (Cui et al. 2000, ApJ 535, L123) and radio emission (Pooley & Hjellming, IAUC #7278).

  12. Optical and near-IR observations of XTE J1859+226

    NASA Astrophysics Data System (ADS)

    Hynes, R. I.; Haswell, C. A.; Norton, A. J.; Chaty, S.; Rolfe, D. J.; Lott, D. A.; Solheim, J.-E.; Ostensen, R.; Garcia, R. A.; Fried, R.; O'Brien, K.; Horne, K.; Ioannou, Z.; Shafter, A.; Abbott, T. M. C.; Krisciunas, K.; Ivison, R. J.; Sano, Y.; Chen, W.; Shrader, C.; Livio, M.; Robinson, E. L.; Wagner, R. M.

    1999-10-01

    Following optical and near-infrared monitoring of XTE J1859+226 (IAUC #7279, #7284), HST/STIS observations were performed on Oct 18.10-18.38 spanning 112-1026nm. The UV spectrum shows broad (12000km/s FWZI) and deep Lyman alpha absorption, strong CIV 155nm emission (EW 1.1nm, 4000km/s FWZI) and weaker emission lines of CIII, NV, OIII, OIV, OV, SiIV and HeII. Sharp absorption lines of SiII, SiIII, MgII and other species also appear with possible interstellar origin.

  13. ATCA detection of increased radio emission from XTE J1752-223

    NASA Astrophysics Data System (ADS)

    Brocksopp, Catherine; Corbel, Stephane; Tzioumis, Tasso; Fender, Rob; Coriat, Mickael

    2010-01-01

    Following the announcement that the new X-ray transient source, XTE J1752-223 (ATel. 2258), is making a transition from the hard to the intermediate state (ATel. 2387, 2391, 2396), we have observed the radio counterpart with the Australia Telescope Compact Array and the new CABB back-end. The radio source has risen from the previous ~2 mJy plateau to 20 mJy at 1.2, 2.5, 5.5, 9, 17, 19 GHz on January 21.

  14. The Magnetar Nature and the Outburst Mechanism of a Transient Anomalous X-ray Pulsar

    NASA Technical Reports Server (NTRS)

    Guver, Tolga; Ozel, Feryal; Gogus, Ersin; Kouveliotou, Chryssa

    2007-01-01

    Anomalous X-ray Pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spindowns. However, a direct measurement of their surface field strengths has not been made to date. It is also not known whether AXP outbursts result from changes in the neutron star magnetic field or crust properties. Here we report the first, spectroscopic measurement of the surface magnetic field strength of an AXP, XTE J1810-197, and solidify its magnetar nature. The field strength obtained from detailed spectral analysis and modeling is remarkably close to the value inferred from the rate of spindown of this source and remains nearly constant during numerous observations spanning over two orders of magnitude in source flux. The surface temperature, on the other hand, declines steadily and dramatically following the 2003 outburst of this source. Our findings demonstrate that heating occurs in the upper neutron star crust during an outburst and sheds light on the transient behaviour of AXPs.

  15. Detailed Physical Modeling Reveals the Magnetar Nature of a Transient Anomalous X-ray Pulsar

    NASA Technical Reports Server (NTRS)

    Guever, T.; Oezel, F.; Goegues, E.; Kouveliotou, C.

    2007-01-01

    Anomalous X-ray Pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spindowns. However, a direct measurement of their surface field strengths has not been made to date. It is also not known whether AXP outbursts result from changes in the neutron star magnetic field or crust properties. Here we report the first, spectroscopic measurement of the surface magnetic field strength of an AXP, XTE J1810-197, and solidify its magnetar nature. The field strength obtained from detailed spectral analysis and modeling is remarkably close to the value inferred from the rate of spindown of this source and remains nearly constant during numerous observations spanning over two orders of magnitude in source flux. The surface temperature, on the other hand, declines steadily and dramatically following the 2003 outburst of this source. Our findings demonstrate that heating occurs in the upper neutron star crust during an outburst and sheds light on the transient behaviour of AXPs.

  16. Theory of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Bucciantini, N.

    2008-02-01

    Our understanding of Pulsar Wind Nebulae (PWNe), has greatly improved in the last years thanks to unprecedented high resolution images taken from the HUBBLE, CHANDRA and XMM satellites. The discovery of complex but similar inner features, with the presence of unexpected axisymmetric rings and jets, has prompted a new investigation into the dynamics of the interaction of the pulsar winds with the surrounding SNR, which, thanks to the improvement in the computational resources, has let to a better understanding of the properties of these objects. On the other hand the discovery of non-thermal emission from bow shock PWNe, and of systems with a complex interaction between pulsar and SNR, has led to the development of more reliable evolutionary models. I will review the standard theory of PWNe, their evolution, and the current status in the modeling of their emission properties, in particular I will show that our evolutionary models are able to describe the observations, and that the X-ray emission can now be reproduced with sufficient accuracy, to the point that we can use these nebulae to investigate fundamental issues as the properties of relativistic outflows and particle acceleration.

  17. Searching for Pulsars Using Image Pattern Recognition

    NASA Astrophysics Data System (ADS)

    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

  18. Searching for pulsars using image pattern recognition

    SciTech Connect

    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. E-mail: berndsen@phas.ubc.ca; 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

  19. THE TIMING OF NINE GLOBULAR CLUSTER PULSARS

    SciTech Connect

    Lynch, Ryan S.; Freire, Paulo C. C.; Ransom, Scott M.; Jacoby, Bryan A. E-mail: pfreire@mpifr-bonn.mpg.de E-mail: bryan.jacoby@gmail.com

    2012-02-01

    We have used the Robert C. Byrd Green Bank Telescope to time nine previously known pulsars without published timing solutions in the globular clusters (GCs) M62, NGC 6544, and NGC 6624. We have full timing solutions that measure the spin, astrometric, and (where applicable) binary parameters for six of these pulsars. The remaining three pulsars (reported here for the first time) were not detected enough to establish solutions. We also report our timing solutions for five pulsars with previously published solutions, and find good agreement with other authors, except for PSR J1701-3006B in M62. Gas in this system is probably responsible for the discrepancy in orbital parameters, and we have been able to measure a change in the orbital period over the course of our observations. Among the pulsars with new solutions we find several binary pulsars with very low mass companions (members of the so-called 'black widow' class) and we are able to place constraints on the mass-to-light ratio in two clusters. We confirm that one of the pulsars in NGC 6624 is indeed a member of the rare class of non-recycled pulsars found in GCs. We have also measured the orbital precession and Shapiro delay for a relativistic binary in NGC 6544. If we assume that the orbital precession can be described entirely by general relativity, which is likely, we are able to measure the total system mass (2.57190(73) M{sub Sun }) and companion mass (1.2064(20) M{sub Sun }), from which we derive the orbital inclination (sin i = 0.9956(14)) and the pulsar mass (1.3655(21) M{sub Sun }), the most precise such measurement ever obtained for a millisecond pulsar. The companion is the most massive known around a fully recycled pulsar.

  20. Magnetoreflectivity of Pb{sub 1{minus}x}Eu{sub x}Te epilayers and PbTe/Pb{sub 1{minus}x}Eu{sub x}Te multiple quantum wells

    SciTech Connect

    Yuan, S.; Krenn, H.; Springholz, G.; Ueta, Y.; Bauer, G.; McCann, P.J.

    1997-02-01

    Molecular-beam epitaxy grown n-type Pb{sub 1{minus}x}Eu{sub x}Te epilayers (x{le}0.034) and PbTe/Pb{sub 1{minus}x}Eu{sub x}Te (x{le}0.039) multiple-quantum-well (MQW) samples were studied by magnetoreflectivity in the Faraday configuration (B{parallel}[111]) for magnetic fields up to 6T at 4.2 K. Since the IV-VI lead salt compounds are quite polar semiconductors, resonant electron-longitudinal-optic- (LO-) phonon coupling (Fr{umlt o}hlich coupling) modifies the cyclotron resonance (CR) energies in the Pb{sub 1{minus}x}Eu{sub x}Te single epilayers for the three-dimensional (3D) case. Due to the many-valley band structure {ital two} different Fr{umlt o}hlich coupling constants are relevant. However, the CR energies of quasi-two-dimensional (2D) carriers in PbTe wells [n{sup 2D}=(1.5{minus}3){times}10{sup 11}cm{sup {minus}2}] of PbTe/Pb{sub 1{minus}x}Eu{sub x}Te MQW samples do {ital not} exhibit a significant resonant electron-LO-phonon interaction. This observation is attributed to finite-electron concentration effects, in particular, to a partial filling of the lowest 2D Landau spin level. The static and dynamic screening of the polar interaction are considered as well, but are ruled out as an explanation for the absence of any remarkable polaron correction to the CR energies of electrons in the PbTe quantum wells for the range of carrier concentrations investigated. The magnetoreflectivity spectra of Pb{sub 1{minus}x}Eu{sub x}Te single layers and PbTe/Pb{sub 1{minus}x}Eu{sub x}Te quantum well samples are simulated numerically, using a model for the dielectric response of which also includes the electron-LO-phonon interaction. The transverse and longitudinal masses, and thus also the interband momentum matrix elements are determined for Pb{sub 1{minus}x}Eu{sub x}Te as a function of the composition up to x{lt}0.034. It is found that the transverse mass {ital increases} with Eu content, whereas the longitudinal one nearly stays constant. (Abstract Truncated)

  1. Braking index of isolated pulsars

    NASA Astrophysics Data System (ADS)

    Hamil, O.; Stone, J. R.; Urbanec, M.; Urbancová, G.

    2015-03-01

    Isolated pulsars are rotating neutron stars with accurately measured angular velocities Ω , and their time derivatives that show unambiguously that the pulsars are slowing down. Although the exact mechanism of the spin-down is a question of detailed debate, the commonly accepted view is that it arises through emission of magnetic dipole radiation (MDR) from a rotating magnetized body. Other processes, including the emission of gravitational radiation, and of relativistic particles (pulsar wind), are also being considered. The calculated energy loss by a rotating pulsar with a constant moment of inertia is assumed proportional to a model dependent power of Ω . This relation leads to the power law Ω ˙ =-K Ωn where n is called the braking index. The MDR model predicts n exactly equal to 3. Selected observations of isolated pulsars provide rather precise values of n , individually accurate to a few percent or better, in the range 1

  2. The Binary Pulsar: Gravity Waves Exist.

    ERIC Educational Resources Information Center

    Will, Clifford

    1987-01-01

    Reviews the history of pulsars generally and the 1974 discovery of the binary pulsar by Joe Taylor and Russell Hulse specifically. Details the data collection and analysis used by Taylor and Hulse. Uses this discussion as support for Albert Einstein's theory of gravitational waves. (CW)

  3. Neutron Stars and the Discovery of Pulsars.

    ERIC Educational Resources Information Center

    Greenstein, George

    1985-01-01

    Part one recounted the story of the discovery of pulsars and examined the Crab Nebula, supernovae, and neutron stars. This part (experts from the book "Frozen Star") shows how an understanding of the nature of pulsars allowed astronomers to tie these together. (JN)

  4. Report on a Stable New Pulsar

    DTIC Science & Technology

    1985-12-01

    Figure 3). Only three 1 d pulsars are known to pulse in optical light (PSR0531+21 in the Crab Nebula , PSR0833-45 in the Vela supernova remnant, and...PSR0540-693 in t he Large Magellanic Cloud) and only one of these (the Crab Nebula pulsar) has been found ta pulse in all wavelength bands from I

  5. Radio polarimetry of Galactic Centre pulsars

    NASA Astrophysics Data System (ADS)

    Schnitzeler, D. H. F. M.; Eatough, R. P.; Ferrière, K.; Kramer, M.; Lee, K. J.; Noutsos, A.; Shannon, R. M.

    2016-07-01

    To study the strength and structure of the magnetic field in the Galactic Centre (GC), we measured Faraday rotation of the radio emission of pulsars which are seen towards the GC. Three of these pulsars have the largest rotation measures (RMs) observed in any Galactic object with the exception of Sgr A⋆. Their large dispersion measures, RMs and the large RM variation between these pulsars and other known objects in the GC implies that the pulsars lie in the GC and are not merely seen in projection towards the GC. The large RMs of these pulsars indicate large line-of-sight magnetic field components between ˜ 16 and 33 μG; combined with recent model predictions for the strength of the magnetic field in the GC this implies that the large-scale magnetic field has a very small inclination angle with respect to the plane of the sky (˜12°). Foreground objects like the Radio Arc or possibly an ablated, ionized halo around the molecular cloud G0.11-0.11 could contribute to the large RMs of two of the pulsars. If these pulsars lie behind the Radio Arc or G0.11-0.11 then this proves that low-scattering corridors with lengths ≳100 pc must exist in the GC. This also suggests that future, sensitive observations will be able to detect additional pulsars in the GC. Finally, we show that the GC component in our most accurate electron density model oversimplifies structure in the GC.

  6. INTEGRAL Long-Term Monitoring of the Supergiant Fast X-Ray Transient XTE J1739-302

    NASA Technical Reports Server (NTRS)

    Blay, P.; Martinez-Nunez, S.; Negueruela, I.; Pottschmidt, K.; Smith, D. M.; Torrejon, J. M.; Reig, P.; Kretschmar, P.; Kreykenbohm, I.

    2008-01-01

    Context. In the past few years, a new class of High Mass X-Ray Binaries (HMXRB) has been claimed to exist, the Supergiant Fast X-ray Transients (SFXT). These are X-ray binary systems with a compact companion orbiting a supergiant star which show very short and bright outbursts in a series of activity periods overimposed on longer quiescent periods. Only very recently the first attempts to model the behaviour of these sources have been published, some of them within the framework of accretion from clumpy stellar winds. Aims. Our goal is to analyze the properties of XTE J1739-302/IGR J17391-3021 within the context of the clumpy structure of the supergiant wind. Methods. We have used INTEGRAL and RXTE/PCA observations in order to obtain broad band (1 - 200 keV) spectra and light curves of XTE J1739-302 and investigate its X-ray spectrum and temporal variability. Results. We have found that XTE J1739-302 follows a much more complex behaviour than expected. Far from presenting a regular variability pattern, XTE J1739-302 shows periods of high, intermediate, and low flaring activity.

  7. Discovery of a new type of topological Weyl fermion semimetal state in MoxW1-xTe2.

    PubMed

    Belopolski, Ilya; Sanchez, Daniel S; Ishida, Yukiaki; Pan, Xingchen; Yu, Peng; Xu, Su-Yang; Chang, Guoqing; Chang, Tay-Rong; Zheng, Hao; Alidoust, Nasser; Bian, Guang; Neupane, Madhab; Huang, Shin-Ming; Lee, Chi-Cheng; Song, You; Bu, Haijun; Wang, Guanghou; Li, Shisheng; Eda, Goki; Jeng, Horng-Tay; Kondo, Takeshi; Lin, Hsin; Liu, Zheng; Song, Fengqi; Shin, Shik; Hasan, M Zahid

    2016-12-05

    The recent discovery of a Weyl semimetal in TaAs offers the first Weyl fermion observed in nature and dramatically broadens the classification of topological phases. However, in TaAs it has proven challenging to study the rich transport phenomena arising from emergent Weyl fermions. The series MoxW1-xTe2 are inversion-breaking, layered, tunable semimetals already under study as a promising platform for new electronics and recently proposed to host Type II, or strongly Lorentz-violating, Weyl fermions. Here we report the discovery of a Weyl semimetal in MoxW1-xTe2 at x=25%. We use pump-probe angle-resolved photoemission spectroscopy (pump-probe ARPES) to directly observe a topological Fermi arc above the Fermi level, demonstrating a Weyl semimetal. The excellent agreement with calculation suggests that MoxW1-xTe2 is a Type II Weyl semimetal. We also find that certain Weyl points are at the Fermi level, making MoxW1-xTe2 a promising platform for transport and optics experiments on Weyl semimetals.

  8. A radio pulsar spinning at 716 Hz.

    PubMed

    Hessels, Jason W T; Ransom, Scott M; Stairs, Ingrid H; Freire, Paulo C C; Kaspi, Victoria M; Camilo, Fernando

    2006-03-31

    We have discovered a 716-hertz eclipsing binary radio pulsar in the globular cluster Terzan 5 using the Green Bank Telescope. It is the fastest spinning neutron star found to date, breaking the 24-year record held by the 642-hertz pulsar B1937+21. The difficulty in detecting this pulsar, because of its very low flux density and high eclipse fraction (approximately 40% of the orbit), suggests that even faster spinning neutron stars exist. If the pulsar has a mass less than twice the mass of the Sun, then its radius must be constrained by the spin rate to be <16 kilometers. The short period of this pulsar also constrains models that suggest that gravitational radiation, through an r-mode (Rossby wave) instability, limits the maximum spin frequency of neutron stars.

  9. Searching for Pulsars with the SKA

    NASA Astrophysics Data System (ADS)

    Ransom, Scott

    2007-12-01

    One of the SKA Key Science Projects involves "strong field tests of gravity using pulsars and black holes". However, we currently don't know of any pulsar - black hole binaries! Another component of this key science project involves the detection of nano-Hertz gravitational waves using an ensemble of many tens or hundreds of very high-precision millisecond pulsars, many of which are also, as yet, unknown. It is clear that some of the first major pulsar projects conducted with early phases of the SKA will involve large-area surveys. Given the likely nature of the mid-frequency-range SKA (i.e. large numbers of small dishes), such surveys will be incredibly challenging, and will require extremely large data and computational rates. However, the technical issues are likely surmountable, and the resulting surveys will find thousands of new pulsars, many of which will be useful for these and other basic physics tests.

  10. SUB-LUMINOUS {gamma}-RAY PULSARS

    SciTech Connect

    Romani, R. W.; Kerr, M.; Craig, H. A.; Johnston, S.; Cognard, I.; Smith, D. A.

    2011-09-01

    Most pulsars observed by the Fermi Large Area Telescope have {gamma}-ray luminosities scaling with spin-down power E-dot as L{sub {gamma}}{approx}(E-dot x 10{sup 33} erg s{sup -1}){sup 1/2}. However, there exist one detection and several upper limits an order of magnitude or more fainter than this trend. We describe these 'sub-luminous' {gamma}-ray pulsars and discuss the case for this being an orientation effect. Of the 12 known young radio pulsars with E-dot >10{sup 34} erg s{sup -1} and d {<=} 2 kpc several are substantially sub-luminous. The limited available geometrical constraints favor aligned geometries for these pulsars, although no one case for alignment is compelling. In this scenario GeV emission detected from such sub-luminous pulsars can be due to a lower altitude, lower-power accelerator gap.

  11. Relativistic Iron Emission and Disk Reflection in Galactic Microquasar XTE J1748-288

    NASA Technical Reports Server (NTRS)

    Miller, J. M.; Fox, D. W.; Matteo, T. DI; Wijnands, R.; Belloni, T.; Pooley, D.; Kouveliotou, C.; Lewin, W. H. G.

    2001-01-01

    We report evidence for an Fe K(alpha) fluorescence line feature and disk reflection in the very high, high-, and low-state X-ray spectra of the Galactic microquasar XTE J1748-288 during its 1998 June outburst. Spectral analyses are made on data gathered throughout the outburst by the Rossi X-Ray Timing Explorer Proportional Counter Array. Gaussian line, relativistic disk emission line, and ionized disk reflection models are fitted to the data. In the very high state the line profile appears strongly redshifted, consistent with disk emission from the innermost stable orbits around a maximally rotating Kerr black hole. In the high state the line profile is less redshifted and increasingly prominent. The low-state line profile is very strong (approx. 0.5 keV equivalent width) and centered at 6.7 +/- 0.10 keV; disk line emission model fits indicate that the inner edge of the disk fluctuates between approx. 20Rg and approx. 100Rg in this state. The disk reflection fraction is traced through the outburst; reflection from an ionized disk is preferred in the very high and high states, and reflection from a relatively neutral disk is preferred in the low state. We discuss the implications of our findings for the binary system dynamics and accretion flow geometry in XTE J1748-288.

  12. Relativistic Iron Emission and Disk Reflection in Galactic Microquasar XTE J1748-288

    NASA Technical Reports Server (NTRS)

    Miller, J. M.; Fox, D. W.; DiMatteo, T.; Wijnands, R.; Belloni, T.; Pooley, D.; Kouveliotou, C.; Lewin, W. H. G.

    2001-01-01

    We report evidence for an Fe K-alpha fluorescence line feature and disk reflection in the very high, high-, and low-state X-ray spectra of the Galactic microquasar XTE J1748 - 288 during its 1998 June outburst. Spectral analyses are made on data gathered throughout the outburst by the Rossi X-Ray Timing Explorer Proportional Counter Array. Gaussian line, relativistic disk emission line, and ionized disk reflection models are fitted to the data. In the very high state the line profile appears strongly redshifted, consistent with disk emission from the innermost stable orbits around a maximally rotating Kerr black hole. In the high state the line profile is less redshifted and increasingly prominent. The low-state line profile is very strong (approx. 0.5 keV equivalent width) and centered at 6.7 +/- 0.10 keV; disk line emission model fits indicate that the inner edge of the disk fluctuates between approx. 20R(sub g) and - approx. 100R(sub g) in this state. The disk reflection fraction is traced through the outburst; reflection from an ionized disk is preferred in the very high and high states, and reflection from a relatively neutral disk is preferred in the low state. We discuss the implications of our findings for the binary system dynamics and accretion flow geometry in XTE J1748 - 288.

  13. Phase tracking for pulsar navigation with Doppler frequency

    NASA Astrophysics Data System (ADS)

    Xinyuan, Zhang; Ping, Shuai; Liangwei, Huang

    2016-12-01

    Doppler frequency in pulsar navigation is an effect caused by spacecraft and pulsar motion, which would worsen the pulsar navigation accuracy. To describe this influence, we establish the Doppler frequency measurement model based on pulsar timing. With this model, we describe the relationship between the phase estimation performance and the observation time when Doppler frequency exists. To reduce the pulsar navigation error due to the Doppler frequency, we designed the phase tracking loop for the pulsar navigation. The pulsar frequency can be modified before the phase estimation. As a result, the impact of the Doppler frequency could be lessened, and the observation interval lengths can be lengthened to improve the phase estimation performance.

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

    SciTech Connect

    Knispel, B.; Kim, H.; Allen, B.; Aulbert, C.; Bock, O.; Eggenstein, H.-B.; Fehrmann, H.; Machenschalk, B.; Eatough, R. P.; Keane, E. F.; Kramer, M.; Anderson, D.; Crawford, F.; Rastawicki, D.; Hammer, D.; Papa, M. A.; Siemens, X.; Lyne, A. G.; Miller, R. B.; Sarkissian, J.; 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.

  15. The Guitar Nebula, Bow Shocks From High Velocity Pulsars, and Companions of Recycled Pulsars

    NASA Astrophysics Data System (ADS)

    Lundgren, S. C.; Cordes, J. M.; Romani, R. W.

    1992-12-01

    We report results of optical studies of neutron star interactions with companion objects and the surrounding medium. In Hα observations of 11 high velocity, high spindown energy pulsars we have discovered one spectacular bow shock nebula, the Guitar Nebula, produced by the motion of the pulsar, PSR 2224+65, through partially neutral gas. One other pulsar, PSR 0136+57, has a faint feature near the pulsar position with a nonstellar morphology. We discuss the possibility that this is another shock and give upper limits on shock emission for the rest of the pulsars. Further, we consider possible scaling of shock emission with pulsar spindown energy and velocity, and detectability of shocks in other pulsars. Shocks may even reveal the existence of neutron stars not detectable as pulsars due to beaming or lack of pulsed radio emission. Our observations of several binary millisecond pulsars show some intriquing counterparts in some cases and allow strong limits to be placed on the magnitude of any counterparts in others. In pulsars 1534+12 and 1953+29 optical counterparts near the pulsar position are most likely chance coincidence with foreground stars. We imaged PSR 1257+12 in the hope of seeing the remnants of the disk which resulted in formation of planets or another pulsar wind driven shock nebula. We place upper limits on optical emission from nebulosity in the vicinity of the pulsar. This work was supported by grants from NSF, NASA and the National Astronomy and Ionosphere Center which operates Arecibo Observatory under contract with the NSF.

  16. A Pulsar Eases Off the Brakes

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-10-01

    In 2006, pulsar PSR 18460258 unexpectedly launched into a series of energetic X-ray outbursts. Now a study has determined that this event may have permanently changed the behavior of this pulsar, raising questions about our understanding of how pulsars evolve.Between CategoriesA pulsar a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation can be powered by one of three mechanisms:Rotation-powered pulsars transform rotational energy into radiation, gradually slowing down in a predictable way.Accretion-powered pulsars convert the gravitational energy of accreting matter into radiation.Magnetars are powered by the decay of their extremely strong magnetic fields.Astronomical classification often results in one pesky object that doesnt follow the rules. In this case, that object is PSR 18460258, a young pulsar categorized as rotation-powered. But in 2006, PSR 18460258 suddenly emitted a series of short, hard X-ray bursts and underwent a flux increase behavior that is usually only exhibited by magnetars. After this outburst, it returned to normal, rotation-powered-pulsar behavior.Since the discovery of this event, scientists have been attempting to learn more about this strange pulsar that seems to straddle the line between rotation-powered pulsars and magnetars.Unprecedented DropOne way to examine whats going on with PSR 18460258 is to evaluate whats known as its braking index, a measure of how quickly the pulsars rotation slows down. For a rotation-powered pulsar, the braking index should be roughly constant. The pulsar then slows down according to a fixed power law, where the slower it rotates, the slower it slows down.In a recent study, Robert Archibald (McGill University) and collaborators report on 7 years worth of timing observations of PSR 18460258 after its odd magnetar-like outburst. They then compare these observations to 6.5 years of data from before the outburst. The team finds that the braking index for this bizarre

  17. Outflows from Supersonically-Moving Pulsars

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    Pulsar wind nebulae (PWNe) are sources of nonthermal X-ray emission and prominent sites of particle acceleration. Among other parameters, the PWN appearance depends on the pulsar velocity. If a pulsar moves with a supersonic speed, the ram pressure exceeds the ambient medium pressure, resulting in a bow shock PWN with a tail behind the pulsar. We report on Chandra observations of extended pulsar tails behind PSR J1509-5850 and J1747-2958 ("the Mouse"), and the discovery of a puzzling outflow (in the J1509-5850 PWN) strongly misaligned with the pulsar's direction of motion. We resolve the structures of the heads of the two PWNe and interpret them in light of pulsar wind models. We perform spatially resolved spectral measurements and find only marginal evidence of cooling in the long tail of PSR J1509-5850. The morphologies of the PWN heads and the extended tails are discussed and compared with those of other bow shock PWNe detected by Chandra. A possible unifying scheme will be discussed.

  18. Fluctuating neutron star magnetosphere: braking indices of eight pulsars, frequency second derivatives of 222 pulsars and 15 magnetars

    NASA Astrophysics Data System (ADS)

    Ou, Z. W.; Tong, H.; Kou, F. F.; Ding, G. Q.

    2016-04-01

    Eight pulsars have low braking indices, which challenge the magnetic dipole braking of pulsars. 222 pulsars and 15 magnetars have abnormal distribution of frequency second derivatives, which also make contradiction with classical understanding. How neutron star magnetospheric activities affect these two phenomena are investigated by using the wind braking model of pulsars. It is based on the observational evidence that pulsar timing is correlated with emission and both aspects reflect the magnetospheric activities. Fluctuations are unavoidable for a physical neutron star magnetosphere. Young pulsars have meaningful braking indices, while old pulsars' and magnetars' fluctuation item dominates their frequency second derivatives. It can explain both the braking index and frequency second derivative of pulsars uniformly. The braking indices of eight pulsars are the combined effect of magnetic dipole radiation and particle wind. During the lifetime of a pulsar, its braking index will evolve from three to one. Pulsars with low braking index may put strong constraint on the particle acceleration process in the neutron star magnetosphere. The effect of pulsar death should be considered during the long term rotational evolution of pulsars. An equation like the Langevin equation for Brownian motion was derived for pulsar spin-down. The fluctuation in the neutron star magnetosphere can be either periodic or random, which result in anomalous frequency second derivative and they have similar results. The magnetospheric activities of magnetars are always stronger than those of normal pulsars.

  19. Classical Accreting Pulsars with NICER

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2014-01-01

    Soft excesses are very common center dot Lx > 1038 erg/s - reprocessing by optically thick material at the inner edge of the accretion disk center dot Lx < 1036 erg/s - photoionized or collisionally heated diffuse gas or thermal emission from the NS surface center dot Lx 1037 erg/s - either or both types of emission center dot NICER observations of soft excesses in bright X-ray pulsars combined with reflection modeling will constrain the ionization state, metalicity and dynamics of the inner edge of the magnetically truncated accretion disk Reflection models of an accretion disk for a hard power law - Strong soft excess below 3 keV from hot X-ray heated disk - For weakly ionized case: strong recombination lines - Are we seeing changes in the disk ionization in 4U1626-26? 13 years of weekly monitoring with RXTE PCA center dot Revealed an unexpectedly large population of Be/X-ray binaries compared to the Milky Way center dot Plotted luminosities are typical of "normal" outbursts (once per orbit) center dot The SMC provides an excellent opportunity to study a homogenous population of HMXBs with low interstellar absorption for accretion disk studies. Monitoring with NICER will enable studies of accretion disk physics in X-ray pulsars center dot The SMC provides a potential homogeneous low-absorption population for this study center dot NICER monitoring and TOO observations will also provide measurements of spinfrequencies, QPOs, pulsed fluxes, and energy spectra.

  20. Age Discrepancy Throws Pulsar Theories into Turmoil

    NASA Astrophysics Data System (ADS)

    2002-03-01

    Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have found a pulsar -- a spinning, superdense neutron star -- that apparently is considerably younger than previously thought. This finding, combined with the discovery in 2000 of a pulsar that was older than previously thought, means that many assumptions astronomers have made about how pulsars are born and age must be reexamined, according to the researchers. Supernova Remnant and Pulsar -- Click on image for larger view Infrared Image of Supernova Remnant; Dashed Line and Arrow Indicate Pulsar's Motion Detected by VLA "We are learning that each individual pulsar is a very complicated object, and we should assume nothing about it," said Bryan Gaensler, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. "Our work makes it more difficult to put pulsars into neat categories, but ultimately will yield new insights into how pulsars are born," he added. The research is reported in the March 10 edition of the Astrophysical Journal Letters. The astronomers studied a pulsar called B1951+32 and a supernova remnant called CTB 80, both nearly 8,000 light-years from Earth. The supernova remnant is the shell of debris from the explosion of a giant star. The explosion resulted from the giant star's catastrophic collapse into the superdense neutron star. By observing the pulsar and the supernova remnant from 1989 to 2000 with the VLA, the scientists were able to measure the movement of the pulsar, which, they found, is moving directly outward from the center of the shell of explosion debris. "We've always felt that, if you see a pulsar and a supernova remnant close together, the pulsar had been born in an explosion at the center of the supernova remnant, but this is the first time that actual observational measurement shows a pulsar moving away from the center of the supernova remnant. It's nice to finally have such an example," said Joshua Migliazzo of the Center for

  1. Limits to the Stability of Pulsar Time

    NASA Technical Reports Server (NTRS)

    Petit, Gerard

    1996-01-01

    The regularity of the rotation rate of millisecond pulsars is the underlying hypothesis for using these neutron stars as 'celestial clocks'. Given their remote location in our galaxy and to our lack of precise knowledge on the galactic environment, a number of phenomena effect the apparent rotation rate observed on Earth. This paper reviews these phenomena and estimates the order of magnitude of their effect. It concludes that an ensemble pulsar time based on a number of selected millisecond pulsars should have a fractional frequency stability close to 2 x 10(sup -15) for an averaging time of a few years.

  2. Frequency dependence of pulsar integrated profiles

    SciTech Connect

    Thorsett, S.E. )

    1991-08-01

    The dependence of component separation on observing frequency has been studied for seven pulsars that exhibit double- or multiple-component average profiles. In each case, a review of all available data shows a smooth variation of given form. No evidence is found for a 'break frequency' at which the separation behavior discretely changes. It is argued that previous reports of such a discontinuity are due to insufficiently sampled data together with a prejudice toward pure power-law functional behaviors. The absence of such a break has implications for theories of the pulsar emission mechanism and of the propagation of radio waves in the pulsar magnetosphere. 44 refs.

  3. A digital pulsar backend based on FPGA

    NASA Astrophysics Data System (ADS)

    Luo, Jin-Tao; Chen, Lan; Han, Jin-Lin; Esamdin, Ali; Wu, Ya-Jun; Li, Zhi-Xuan; Hao, Long-Fei; Zhang, Xiu-Zhong

    2017-01-01

    A digital pulsar backend based on a Field Programmable Gate Array (FPGA) is developed. It is designed for incoherent de-dispersion of pulsar observations and has a maximum bandwidth of 512 MHz. The channel bandwidth is fixed to 1 MHz, and the highest time resolution is 10 {{μ }} s. Testing observations were carried out using the Urumqi 25-m telescope administered by Xinjiang Astronomical Observatory and the Kunming 40-m telescope administered by Yunnan Observatories, targeting PSR J0332+5434 in the L band and PSR J0437–4715 in the S band, respectively. The successful observation of PSR J0437–4715 demonstrates its ability to observe millisecond pulsars.

  4. Pulsar Emission Geometry and Accelerating Field Strength

    DTIC Science & Technology

    2011-11-01

    ar X iv :1 11 1. 03 25 v1 [ as tr o- ph .H E ] 1 N ov 2 01 1 2011 Fermi Symposium, Roma., May. 9-12 1 Pulsar Emission Geometry and Accelerating...observations of gamma-ray pulsars have opened a new window to understanding the generation mechanisms of high-energy emission from these systems. The high...the Vela and CTA 1 pulsars with simulated high-energy light curves generated from geometrical representations of the outer gap and slot gap emission

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

    SciTech Connect

    Li, L.; Tong, H.; Yan, W. M.; Yuan, J. P.; Wang, N.; Xu, R. X.

    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.

  6. Astronomers Discover Fastest-Spinning Pulsar

    NASA Astrophysics Data System (ADS)

    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

  7. A versatile 50 ft-lb-sec reaction wheel for TRMM and XTE missions

    NASA Astrophysics Data System (ADS)

    Bialke, Bill

    A 50 ft-lb-sec Reaction Wheel is being manufactured by ITHACO, Inc. for NASA's X-ray Timing Explorer (XTE) and Tropical Rainfall Measuring Mission (TRMM) missions, using the same mechanical assemblies as a similar Reaction Wheel developed by ITHACO for the Air Force's Advanced Research and Global Observation Satellite (ARGOS) (P91-1) mission. The versatile design allows variation in motor torque and speed capability with no mechanical modifications. State of the art ball bearing technology is combined with flight proven materials and conventional fabrication techniques to produce a relaible and manufacturable wheel assembly. An ironless armature brushless DC motor is incorporated for high efficiency and minimum weight. Comprehensive tradeoff analyses from the Reaction Wheel development are discussed for each component, and performance characteristics are presented for design variations from a high torque Reaction Wheel used in a three axis stabilized spacecraft to a low torque Momentum Wheel used in a momentum biased attitude Control System.

  8. Multiwavelength Observations of the Black Hole Candidate XTE J1550-564 during the 2000 Outburst

    NASA Astrophysics Data System (ADS)

    Jain, Raj K.; Bailyn, Charles D.; Orosz, Jerome A.; McClintock, Jeffrey E.; Remillard, Ronald A.

    2001-06-01

    We report optical, infrared, and X-ray light curves for the outburst, in 2000, of the black hole candidate XTE J1550-564. We find that the start of the outburst in the H and V bands precedes that seen in the Rossi X-Ray Timing Explorer All-Sky Monitor by 11.5+/-0.9 and 8.8+/-0.6 days, respectively; a similar delay has been observed in two other systems. About 50 days after the primary maxima in the VIH light curves, we find secondary maxima, most prominently in H. This secondary peak is absent in the X-ray light curve but coincides with a transition to the low/hard state. We suggest that this secondary peak may be due to nonthermal emission associated with the formation of a jet.

  9. The Rossi X-Ray Timing Explorer (XTE) Solar Array Anomaly

    NASA Technical Reports Server (NTRS)

    Gaddy, Edward M.; Kichak, Robert; Niemeyer, Lee; Stegeman, Richard

    2004-01-01

    The XTE was launched December 30, 1995. Shortly after launch, it become apparent that the solar array was not performing as expected. On leaving shadow, the array exhibited many discontinuous drops in current output. The size of each of these drops was consistent with the loss of a part of a sell. The current decreases could not be caused by the loss of an entire circuit. This meant that the array may have had numerous cracked solar cells that opened as array got warmer. Studies performed on the array's qualification panel suggest that the cell cracks may have been cased by extensive tap testing performed on the array and that these cracks were undetectable at room temperature using usual inspection method.

  10. THE MASS OF THE BLACK HOLE IN XTE J1118+480

    SciTech Connect

    Khargharia, Juthika; Froning, Cynthia S.; Robinson, Edward L.; Gelino, Dawn M. E-mail: cynthia.froning@colorado.edu E-mail: dawn@ipac.caltech.edu

    2013-01-01

    We present contemporaneous, broadband, near-infrared spectroscopy (0.9-2.45 {mu}m) and H-band photometry of the black hole X-ray binary, XTE J1118+480. We determined the fractional dilution of the NIR ellipsoidal light curves of the donor star from other emission sources in the system by comparing the absorption features in the spectrum with field stars of known spectral type. We constrained the donor star spectral type to K7 V-M1 V and determined that the donor star contributed 54% {+-} 27% of the H-band flux at the epoch of our observations. This result underscores the conclusion that the donor star cannot be assumed to be the only NIR emission source in quiescent X-ray binaries. The H-band light curve shows a double-humped asymmetric modulation with extra flux at orbital phase 0.75. The light curve was fitted with a donor star model light curve, taking into account a constant second flux component based on the dilution analysis. We also fitted models that included emission from the donor star, a constant component from the accretion disk, and a phase-variable component from the bright spot where the mass accretion stream impacts the disk. These simple models with reasonable estimates for the component physical parameters can fully account for the observed light curve, including the extra emission at phase 0.75. From our fits, we constrained the binary inclination to 68 Degree-Sign {<=} i {<=} 79 Degree-Sign . This leads to a black hole mass of 6.9 M{sub Sun} {<=} M{sub BH} {<=} 8.2 M{sub Sun }. Long-term variations in the NIR light curve shape in XTE J1118+480 are similar to those seen in other X-ray binaries and demonstrate the presence of continued activity and variability in these systems even when in full quiescence.

  11. Gamma ray pulsars. [electron-photon cascades

    NASA Technical Reports Server (NTRS)

    Oegelman, H.; Ayasli, S.; Hacinliyan, A.

    1977-01-01

    Data from the SAS-2 high-energy gamma-ray experiment reveal the existence of four pulsars emitting photons above 35 MeV. An attempt is made to explain the gamma-ray emission from these pulsars in terms of an electron-photon cascade that develops in the magnetosphere of the pulsar. Although there is very little material above the surface of the pulsar, the very intense magnetic fields (10 to the 12th power gauss) correspond to many radiation lengths which cause electrons to emit photons by magnetic bremsstrahlung and which cause these photons to pair-produce. The cascade develops until the mean photon energy drops below the pair-production threshold which is in the gamma-ray range; at this stage, the photons break out from the source.

  12. Quasars, pulsars, black holes and HEAO's

    NASA Technical Reports Server (NTRS)

    Doolitte, R. F.; Moritz, K.; Whilden, R. D. C.

    1974-01-01

    Astronomical surveys are discussed by large X-ray, gamma ray, and cosmic ray instruments carried onboard high-energy astronomy observatories. Quasars, pulsars, black holes, and the ultimate benefits of the new astronomy are briefly discussed.

  13. Multiwavelength Observations of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Slane, Patrick

    The extended nebulae formed as pulsar winds expand into their surroundings provide information about the composition of the winds, the injection history from the host pulsar, and the material into which the nebulae are expanding. Observations from across the electromagnetic spectrum provide constraints on the evolution of the nebulae, the density and composition of the surrounding ejecta, the geometry of the central engines, and the long-term fate of the energetic particles produced in these systems. Such observations reveal the presence of jets and wind termination shocks, time-varying compact emission structures, shocked supernova ejecta, and newly formed dust. Here I provide a broad overview of the structure of pulsar wind nebulae, with specific examples from observations extending from the radio band to very-high-energy γ-rays that demonstrate our ability to constrain the history and ultimate fate of the energy released in the spin-down of young pulsars.

  14. OSSE observations of the Crab pulsar

    NASA Technical Reports Server (NTRS)

    Ulmer, M. P.; Matz, S. M.; Cameron, R. A.; Grabelsky, D. A.; Grove, J. E.; Johnson, W. N.; Jung, G. V.; Kinzer, R. L.; Kurfess, J. D.; Leising, M. D.

    1992-01-01

    Preliminary results are presented of the Compton Gamma Ray Observatory Oriented Scintillation Spectrometer Experiment (OSSE) observations of the Crab pulsar. The pulsar energy spectra and light curves are in general agreement with previous observations, validating the OSSE pulsar data acquisition modes and data analysis algorithms. The data suggest that the spectrum of the pulsar varies throughout the light curve. The 'interpulse' region has a slightly flatter spectrum in the approx. 60 to 250 keV region and a slightly steeper spectrum at higher energies than the two main pulses. No evidence was found for any lines in the spectra with a typical sensitivity of about 10(exp -4) photons/sq cm/s.

  15. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2013-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the role played by the high energy photons released from the pulsar in the ejection of matter from the binary system).

  16. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2014-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6397 at 10cm, for studying the orbital secular evolution, the eclipse region, and the role played by the high energy photons released from the pulsar in the ejection of matter from the binary system.

  17. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2014-04-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the role played by the high energy photons released from the pulsar in the ejection of matter from the binary system).

  18. Outlook for Detecting Gravitational Waves with Pulsars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    Though the recent discovery of GW150914 is a thrilling success in the field of gravitational-wave astronomy, LIGO is only one tool the scientific community is using to hunt for these elusive signals. After 10 years of unsuccessful searching, how likely is it that pulsar-timing-array projects will make their own first detection soon?Frequency ranges for gravitational waves produced by different astrophysical sources. Pulsar timing arrays such as the EPTA and IPTA are used to detect low-frequency gravitational waves generated by the stochastic background and supermassive black hole binaries. [Christopher Moore, Robert Cole and Christopher Berry]Supermassive BackgroundGround-based laser interferometers like LIGO are ideal for probing ripples in space-time caused by the merger of stellar-mass black holes; these mergers cause chirps in the frequency range of tens to thousands of hertz. But how do we pick up the extremely low-frequency, nanohertz background signal caused by the orbits of pairs of supermassive black holes? For that, we need pulsar timing arrays.Pulsar timing arrays are sets of pulsars whose signals are analyzed to look for correlations in the pulse arrival time. As the space-time between us and a pulsar is stretched and then compressed by a passing gravitational wave, the pulsars pulses should arrive a little late and then a little early. Comparing these timing residuals in an array of pulsars could theoretically allow for the detection of the gravitational waves causing them.Globally, there are currently four pulsar timing array projects actively searching for this signal, with a fifth planned for the future. Now a team of scientists led by Stephen Taylor (NASA-JPL/Caltech) has estimated the likelihood that these projects will successfully detect gravitational waves in the future.Probability for SuccessExpected detection probability of the gravitational-wave background as a function of observing time, for five different pulsar timing arrays. Optimistic

  19. Piccard: Pulsar timing data analysis package

    NASA Astrophysics Data System (ADS)

    van Haasteren, Rutger

    2016-10-01

    Piccard is a Bayesian-inference pipeline for Pulsar Timing Array (PTA) data and interacts with Tempo2 (ascl:1210.015) through libstempo. The code is use mainly for single-pulsar analysis and gravitational-wave detection purposes of full Pulsar Timing Array datasets. Modeling of the data can include correlated signals per frequency or modeled spectrum, with uniform, dipolar, quadrupolar, or anisotropic correlations; multiple error bars and EFACs per pulsar; and white and red noise. Timing models can be numerically included, either by using the design matrix (linear timing model), or by calling libstempo for the full non-linear timing model. Many types of samplers are included. For common-mode mitigation, the signals can be reconstructed mitigating arbitrary signals simultaneously.

  20. The origin of the Guitar pulsar

    NASA Astrophysics Data System (ADS)

    Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M.

    2009-11-01

    Among a sample of 140 OB associations and clusters, we want to identify probable parent associations for the Guitar pulsar (PSR B2224+65), which would then also constrain its age. For this purpose, we are using an Euler-Cauchy technique, treating the vertical component of the Galactic potential to calculate the trajectories of the pulsar and each association into the past. To include errors, we use Monte Carlo simulations varying the initial parameters within their error intervals. The whole range of possible pulsar radial velocities is taken into account during the simulations. We find that the Guitar pulsar most probably originated from the Cygnus OB3 association ~0.8Myr ago, inferring a current radial velocity of vr ~ -30kms-1, consistent with the inclination of its bow shock.

  1. The anomalous X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Chen, Rui; Li, Xiangdong

    2002-03-01

    In the last few years it has been recognized that a group of X-ray pulsars have peculiar properties which set them apart from the majority of accreting pulars in X-ray binaries. They are called the Anomalous X-ray Pulsars (AXP). These objects are characterized by very soft X-ray spectra with low and steady X-ray fluxes, narrow-distributed spin periods, steady spin-down, no optical/infrared counterparts. Some of them may associate with supernova remnants. The nature of AXP remains mysterious. It has been suggested that AXP are accreting neutron stars, or solitary "magnetars", neutron stars with super strong magnetic fields (≍1010-1011T). In this paper we review the recent progress in the studies of AXP, and discuss the possible implications from comparison of AXP with other neutron stars, such as radio pulsars, radio quiet X-ray pulsar candidates and soft γ-ray repeaters.

  2. An Independent 1967 Discovery of Pulsars

    NASA Astrophysics Data System (ADS)

    Schisler, Charles

    2008-02-01

    During a 1-year tour of duty at the Ballistic Missile Early Warning Site, Clear Air Force Station, Alaska, pulsed signals unrelated to the station radar were observed. Detection of the 4-min/day sidereal advance in the times of occurrence of the signals showed that they were of astronomical origin. At least ten distinct sources were observed and approximate celestial positions of these sources determined from the azimuth and occurrence time of the signals. The strongest source, first detected in mid-August 1967, was identified with the Crab Nebula. Following the announcement of the discovery of pulsars by the Cambridge group in 1968, it was realised that the detected sources were most likely pulsars. In particular, it is virtually certain that the Crab Nebula source was the Crab pulsar. Following the recent de-activation of the radar system, it is now possible to discuss this independent discovery of pulsars.

  3. Interactive Database of Pulsar Flux Density Measurements

    NASA Astrophysics Data System (ADS)

    Koralewska, O.; Krzeszowski, K.; Kijak, J.; Lewandowski, W.

    2012-12-01

    The number of astronomical observations is steadily growing, giving rise to the need of cataloguing the obtained results. There are a lot of databases, created to store different types of data and serve a variety of purposes, e. g. databases providing basic data for astronomical objects (SIMBAD Astronomical Database), databases devoted to one type of astronomical object (ATNF Pulsar Database) or to a set of values of the specific parameter (Lorimer 1995 - database of flux density measurements for 280 pulsars on the frequencies up to 1606 MHz), etc. We found that creating an online database of pulsar flux measurements, provided with facilities for plotting diagrams and histograms, calculating mean values for a chosen set of data, filtering parameter values and adding new measurements by the registered users, could be useful in further studies on pulsar spectra.

  4. Braking Index of GEMINGA Pulsar

    NASA Astrophysics Data System (ADS)

    Ramanamurthy, P. V.; Mattox, J. R.; EGRET Science Team

    1993-12-01

    The pulsar Geminga, also known as 2CG195+04, IE0630+178 and the faint star G", is a remarkable object in the sense that its energy output is almost all in high energy gamma rays. The pulsar elements of this 237 ms pulsar as given by various authors are surveyed. The braking index, $ n = ftimes ddot f / (dot f)(2) as obtained from the elements given by any one group (Hermsen et al. 1992; Bertsch et al. 1992) based on their own data set appears to be too high or has a very large upper limit compared with 3, the value expected for magnetic dipole radiation. This is largely due to the uncertainty in the value of \\ddot f. It is difficult to carry the absolute phase from one set of observations to another for a variety of reasons. Rather than fitting a polynomial in elapsed time to the event phases over different data sets, we have taken a different approach to determine \\ddot f. Hermsen et al. (1992) and Mattox et al. (1993) have determined f and \\dot f from COS-B and EGRET data respectively at two widely separated epochs. Assuming that there were no glitches, we obtained \\ddot f by dividing the difference in \\dot f values at the two epochs by the time difference between the two epochs; the resulting value of \\ddot f is (4 \\pm 2) times 10^{-26} s^{-3} . Combining this with the f and \\dot f values we obtained a value of (4.5 \\pm 2.3) for the braking index. This value agrees well with the expected. With more observations of Geminga scheduled for the Compton GRO, we expect that the error in \\dot f and consequently the errors in \\ddot f and n$ will decrease further in future. \\leftline{Bertsch et al. (1992) Nature, 357, 306} \\leftline{Hermsen et al. (1992) IAU Circular # 5541} \\leftline{Mattox et al. Proc. 2nd Compton Symp., (September, 1993), College} \\leftline{\\quad Park, Md., U.S.A.}

  5. On the structure of pulsar magnetosphere

    NASA Astrophysics Data System (ADS)

    Nikitina, Elena

    2011-07-01

    The angle BETA between rotation and magnetic axes are calculated by two methods for 283 radio pulsars at the wavelength 10 cm, 132 ones at 20 cm and 80 objects at the wavelength near 30 cm. The common average of the angle BETA is 43.5 degrees. Some effects which can give errors in the values of BETA are discussed. There are no correlations between values of BETA and pulsar ages.

  6. OSSE Observations of the Crab Pulsar

    DTIC Science & Technology

    1994-01-01

    Crab nebula and pulsar (Leventhal, MacCallum, & Watts 1977; Ling et al. 1979; Strickman, Johnson, & Kurfess 1979; Ayre et al. 1983; Agrinier et al...emission from the Crab nebula , as well as detector background. The background portion was then subtracted from the entire light curve. The phase ranges we...detections c) References for previous upper limits d) Based on total Crab nebula plus pulsar spectrum e) Upper limits (3) f) Comments related to

  7. The Future of Pulsar Timing Arrays

    NASA Astrophysics Data System (ADS)

    Stappers, B. W.

    Significant advances have been made in the sensitivity of pulsar timing arrays for the detection of gravitational waves in the last decade. This presentation looked forward to consider where the development of pulsar timing arrays might go as we head towards the Square Kilometre Array (SKA) and then beyond. I reviewed where progress needs to be made in terms of sensitivity to gravitational waves, including improvements to existing observing approaches and new telescopes such as MeerKAT and FAST and techniques like LEAP. The dramatic increase in the number of millisecond pulsars is presented and how that might affect progress towards a first detection is discussed. Developments in analytic techniques were also discussed, including the removal of interstellar medium effects, red noise and pulse profile variations. A summary of how the SKA can contribute through an increased millisecond pulsar population and pulsar timing sensitivity was presented. With the likelihood that the SKA will implement some form of Key Science Project approach, some ideas of how will this affect how the International Pulsar Timing Array effort and how it might evolve into a KSP were discussed.

  8. A novel mechanism for creating double pulsars

    NASA Technical Reports Server (NTRS)

    Sigurdsson, Steinn; Hernquist, Lars

    1992-01-01

    Simulations of encounters between pairs of hard binaries, each containing a neutron star and a main-sequence star, reveal a new formation mechanism for double pulsars in dense cores of globular clusters. In many cases, the two normal stars are disrupted to form a common envelope around the pair of neutron stars, both of which will be spun up to become millisecond pulsars. We predict that a new class of pulsars, double millisecond pulsars, will be discovered in the cores of dense globular clusters. The genesis proceeds through a short-lived double-core common envelope phase, with the envelope ejected in a fast wind. It is possible that the progenitor may also undergo a double X-ray binary phase. Any circular, short-period double pulsar found in the galaxy would necessarily come from disrupted disk clusters, unlike Hulse-Taylor class pulsars or low-mass X-ray binaries which may be ejected from clusters or formed in the galaxy.

  9. DETECTING GRAVITATIONAL WAVE MEMORY WITH PULSAR TIMING

    SciTech Connect

    Cordes, J. M.; Jenet, F. A. E-mail: merlyn@phys.utb.edu

    2012-06-10

    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 Almost-Equal-To 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.

  10. Ion-implantation-induced damage and resonant levels in Pb/sub 1-x/Sn/sub x/Te

    SciTech Connect

    Gresslehner, K.H.; Palmetshofer, L.

    1980-09-01

    The dependence of the carrier concentration on the implantation dose and on the temperature was investigated in ion-implanted thin films of Pb/sub 1-x/Sn/sub x/Te (0< or =x<0.1). By assuming a twofold defect level in the conduction band we are able to fit the experimental results. With increasing tin content the energy of the defect level shifts towards the conduction-band edge. By extending the results to SnTe a general model for the understanding of the electrical properties of ion-implanted Pb/sub 1-x/Sn/sub x/Te (0< or =x< or =1) is suggested.

  11. The imprint of pulsar parameters on the morphology of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Bühler, Rolf; Giomi, Matteo

    2016-11-01

    The morphology of young Pulsar Wind Nebulae (PWN) is largely determined by the properties of the wind injected by the pulsar. We have used a recent parametrization of the wind obtained from force-free electrodynamics simulations of pulsar magnetospheres to simulate nebulae for different sets of pulsar parameters. We performed axisymmetric relativistic magnetohydrodynamics simulations to test the morphology dependence of the nebula on the obliquity of the pulsar and on the magnetization of the pulsar wind. We compare these simulations to the morphology of the Vela and Crab PWN. We find that the morphology of Vela can be reproduced qualitatively if the pulsar obliquity angle is α ≈ 45° and the magnetization of the wind is high (σ0 ≈ 3.0). A morphology similar to the one of the Crab nebula is only obtained for low-magnetization simulations with α ≳ 45°. Interestingly, we find that Kelvin-Helmholtz instabilities produce small-scale turbulences downstream of the reverse shock of the pulsar wind.

  12. Scaling from Jupiter to pulsars and the acceleration of cosmic ray particles by pulsars, 3

    NASA Technical Reports Server (NTRS)

    Fan, C. Y.

    1985-01-01

    An expression for the rate of energy generation by a pulsar an estimate of contribution from all the pulsars in our galaxy to the observed cosmic ray intensity was presented. The theory was then developed to an expanded version, and observational facts supporting the theory were cited.

  13. Disentangling the NIR/optical emission of the black hole XTE J1650-500 during outburst

    NASA Astrophysics Data System (ADS)

    Curran, P. A.; Chaty, S.; Zurita Heras, J. A.

    2012-11-01

    Context. While the sources of X-ray and radio emission in the different states of low-mass X-ray binaries are relatively well understood, the origin of the near-infrared (NIR) and optical emission is more often debated. It is likely that the NIR/optical flux originates from an amalgam of different emission regions, because it occurs at the intersecting wavelengths of multiple processes. Aims: We aim to identify the NIR/optical emission region(s) of one such low-mass X-ray binary and black hole candidate, XTE J1650-500, via photometric, timing, and spectral analyses. Methods: We present unique NIR/optical images and spectra, obtained with the ESO-New Technology Telescope, during the peak of the 2001 outburst of XTE J1650-500. Results: The data suggest that the NIR/optical flux is due to a combination of emission mechanisms including a significant contribution from X-ray reprocessing and, at early times in the hard state, a relativistic jet that is NIR/radio dim compared to similar sources. Conclusions: The jet of XTE J1650-500 is relatively weak compared to that of other black hole low-mass X-ray binaries, possibly because we observe as it is being "turned off" or quenched at the state transition. While there are several outliers to the radio-X-ray correlation of the hard state of low-mass X-ray binaries, XTE J1650-500 is the first example of an outlier to the NIR/optical-X-ray correlation. Based on observations made with the European Southern Observatory telescopes obtained from the ESO/ST-ECF Science Archive Facility.

  14. The black hole candidate XTE J1752-223 towards and in quiescence: optical and simultaneous X-ray-radio observations

    NASA Astrophysics Data System (ADS)

    Ratti, E. M.; Jonker, P. G.; Miller-Jones, J. C. A.; Torres, M. A. P.; Homan, J.; Markoff, S.; Tomsick, J. A.; Kaaret, P.; Wijnands, R.; Gallo, E.; Özel, F.; Steeghs, D. T. H.; Fender, R. P.

    2012-07-01

    We present optical, X-ray and radio observations of the black hole transient (BHT) XTE J1752-223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752-223 is fainter than 24.4 mag in the i' band. A comparison with measurements of the source during its 2009-2010 outburst shows that the outburst amplitude is more than 8 mag in the i' band. Known X-ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital-period system (Porb≲ 6.8 h) with an M type (or later) mass donor, at a distance of 3.5 ≲d≲ 8 kpc. Simultaneous X-ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X-ray and radio flux of XTE J1752-223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low-luminosity end of the X-ray-radio correlation for this source and compared it with other BHTs. We found that XTE J1752-223 adds to the number of outliers with respect to the 'standard' X-ray-radio luminosity relation. Furthermore, XTE J1752-223 is the second source, after the BHT H1743-322, that shows a transition from the region of the outliers towards the 'standard' correlation at low luminosity. Finally, we report on a faint, variable X-ray source we discovered with Chandra at an angular distance of ˜2.9 arcsec to XTE J1752-223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X-ray emission associated with a jet from XTE J1752-223.

  15. On the Origin of Radio Emission in the X-Ray States of XTE J1650-500 during the 2001-2002 Outburst

    NASA Astrophysics Data System (ADS)

    Corbel, S.; Fender, R. P.; Tomsick, J. A.; Tzioumis, A. K.; Tingay, S.

    2004-12-01

    We report on simultaneous radio and X-ray observations of the black hole candidate XTE J1650-500 during the course of its 2001-2002 outburst. The scheduling of the observations allowed us to sample the properties of XTE J1650-500 in different X-ray spectral states, namely, the hard state, the steep power-law state, and the thermal dominant state, according to the recent spectral classification of McClintock & Remillard. The hard state is consistent with a compact jet dominating the spectral energy distribution at radio frequencies; however, the current data suggest that its contribution as direct synchrotron emission at higher energies may not be significant. In that case, XTE J1650-500 may be dominated by Compton processes (either inverse Comptonization of thermal disk photons and/or synchrotron self-Compton radiation from the base of the compact jet) in the X-ray regime. We surprisingly detect a faint level of radio emission in the thermal dominant state that may be consistent with the emission of previously ejected material interacting with the interstellar medium, similar (but on a smaller angular scale) to what was observed in XTE J1550-564 by Corbel and coworkers. Based on the properties of radio emission in the steep power-law state of XTE J1650-500 and taking into account the behavior of other black hole candidates (namely, GX 339-4, XTE J1550-564, and XTE J1859+226) while in the intermediate and steep power-law states, we are able to present a general pattern of behavior for the origin of radio emission in these two states that could be important for understanding the accretion-ejection coupling very close to the black hole event horizon.

  16. Discovery and X-ray Monitoring of a New Black Hole Candidate XTE J1752-223

    NASA Astrophysics Data System (ADS)

    Shaposhnikov, Nikolai; Swank, J. H.; Markwardt, C. B.; Krimm, H.

    2010-03-01

    On October 23, 2009 a new X-ray transient source XTE J1752-223 was discovered by RXTE during observations scanning the Galactic Bulge region. Source identification in the optical, infra-red, and radio immediately followed. The first pointed RXTE observation, three days after the discovery, revealed a very hard non-thermal energy spectrum and strong iron line emission. After the initial rise the source flux leveled off and showed very stable properties for more than a month of monitoring observations until the Sun was too close for RXTE to observe. We analyzed RXTE data collected during this monitoring campaign. The aperiodic fast variability properties are strongly reminiscent of the extreme hard states shown by the well known black hole binary Cygnus X-1, as well as several other black hole candidates. The overall similarity of the source properties to those of other Galactic black holes classify XTE J1752-223 as a new stellar black hole candidate. We compare spectral and variability properties of XTE J1752-223 to Cygnus X-1 and discuss possible implications for various mechanisms of non-thermal emission.

  17. The Velocity Distribution of Isolated Radio Pulsars

    NASA Technical Reports Server (NTRS)

    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

  18. Pulsar-irradiated stars in dense globular clusters

    NASA Technical Reports Server (NTRS)

    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.

  19. Pulsed X-rays from the Vela pulsar

    NASA Technical Reports Server (NTRS)

    Oegelman, H.; Finley, J. P.; Zimmerman, H. U.

    1993-01-01

    An unambiguous detection by the Rosat satellite of pulsed X-ray emission from the Vela pulsar is reported. The pulse signal is soft, appearing mainly at energies less than 1 keV. The Rosat observations resolve the two sources of emission and show that the pointlike emission centered on the pulsars is soft, whereas the emission from the compact nebula is hard. The observations show that Vela more closely resembles older pulsars that the archetypal young pulsar embedded in an SNR.

  20. Basic physics and cosmology from pulsar timing data

    NASA Technical Reports Server (NTRS)

    Taylor, J. H.

    1991-01-01

    Radio pulsars provide unparalleled opportunities for making measurements of astrophysically interesting phenomena. The author concentrates on two particular applications of high precision timing observations of pulsars: tests of relativistic gravitation theory using the binary pulsar 1913+16, and tests of cosmological models using timing data from millisecond pulsars. New upper limits are presented for the energy density of a cosmic background of low frequency gravitational radiation.

  1. The Wind Interaction Regions of the VELA Pulsar: a Pulsar Jet and Bow Shock Nebula

    NASA Astrophysics Data System (ADS)

    Markwardt, Craig Bishop

    The Vela pulsar is a nearby young pulsar actively radiating radio to γ-rays. We present evidence in this work that the Vela pulsar is also interacting with its surroundings via a relativistic wind, which manifests itself as two different nebular structures. ROSAT PSPC observations of the Vela pulsar show that a 45 arcmin long collimated X-ray feature projects from the pulsar. We favor the interpretation that the feature is a 'cocoon' of heated gas formed when a jet outflow from the Vela pulsar interacts with the interior medium of the supernova remnant. This interpretation is consistent with the observed center-filled morphology and spectrum of the cocoon structure. Combined ROSAT + ASCA observations of the 'head' of the cocoon, the point where the jet is believed to interact with the supernova remnant, demonstrate that the spectrum has a thermal peak near 1 keV, but extends to at least 7 keV. No distinct spectral lines are seen. The spectral parameters of the cocoon could be produced by a cocoon with a pulsar jet whose speed is at least 800 km s-1, depending on the angle of inclination. The mechanical power driving the jet is ≥1036 erg s-1, consistent with the Vela pulsar's rotational energy loss rate. On smaller spatial scales, it has been known that the Vela pulsar is surrounded by a 2 arcmin diameter 'compact' nebula which has power law spectral emission. Our ROSAT HRI observations of the region show that the nebula very likely a bow shock structure formed by a nearly isotropic pulsar wind interacting with the supernova remnant. The axis of the nebula is aligned with the pulsar's known proper motion vector. The high particle energies and magnetic fields near the pulsar make the bow shock an ideal environment for generating X-ray synchrotron emission. We show that a full three dimensional model of the nebula, taking into account what is known about the geometry and pulsar wind physics, is consistent with the observations.

  2. BOOK REVIEW: Rotation and Accretion Powered Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, V. M.

    2008-03-01

    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 Mészáros 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

  3. Chandra Associates Pulsar and Historic Supernova

    NASA Astrophysics Data System (ADS)

    2001-01-01

    SAN DIEGO -- Scientists using NASA’s Chandra X-ray Observatory have found new evidence that a pulsar in the constellation of Sagittarius was created when a massive star exploded, witnessed by Chinese astronomers in the year 386 AD. If confirmed, this will be only the second pulsar to be clearly associated with a historic event. These results were presented today by Victoria Kaspi and Mallory Roberts of McGill University at the American Astronomical Society meeting. Also participating in the research were Gautum Vasisht from the Jet Propulsion Laboratory, Eric Gotthelf from Columbia University, Michael Pivovaroff from Therma-Wave, Inc., and Nobuyuki Kawai from the Institute of Physical and Chemical Research, Japan. The scientists used Chandra to locate the pulsar exactly at the geometric center of the supernova remnant known as G11.2-0.3. This location provides very strong evidence that the pulsar, a neutron star that is rotating 14 times a second, was formed in the supernova of 386 AD, and therefore has an age of 1615 years. "Determining the true ages of astronomical objects is notoriously difficult, and for this reason, historical records of supernovas are of great importance,"said Kaspi."In roughly the past 2,000 years, fewer than 10 reports of probable supernovae have been archived mostly by Asian astronomers. Of those handful, the remnant of 1054 AD, the Crab Nebula, was until now the only pulsar whose birth could be associated with a historic event - and, hence, the only neutron star that has a firm age." Between mid-April and mid-May in the year 386 AD, a young "guest star", presumably a supernova, was recorded by Chinese observers in the direction of the sky now known as the constellation of Sagittarius. In the 1970s, radio astronomers discovered an expanding nebula of gas and high-energy particles, called G11.2-0.3, that is believed to be the remnant of that explosion. In 1997, a team of X-ray astronomers used Japan’s ASCA satellite to discover a pulsar

  4. Unusual flux-distance relationship for pulsars suggested by analysis of the Australia national telescopy facility pulsar catalogue

    SciTech Connect

    Singleton, John; Perez, M R; Singleton, J; Ardavan, H; Ardavan, A

    2009-01-01

    We analyze pulsar fluxes at 1400 MHz (S(1400)) and distances d taken from the Australia National Telescope Facility (ATNF) Pulsar Catalogue. Under the assumption that pulsar populations in different parts of the Galaxy are similar, we find that either (a) pulsar fluxes diminish with distance according to a non-standard power law (we suggest S(1400){proportional_to} 1/d rather than {proportional_to} 1/d{sup 2}) or (b) that there are very significant (i.e. order of magnitude) errors in the distance estimates quoted in the ATNF Catalogue. The former conclusion (a) supports a recent model for pulsar emission that has also successfully explained the frequency spectrum of the Crab pulsar over 16 orders of magnitude of frequency, whilst alternative (b) would necessitate a radical re-evaluation of both the dispersion method for estimating pulsar distances and current ideas about the distribution of pulsars within our Galaxy.

  5. Binary Pulsar B1259-63 Spectrum Evolution and Classification of Pulsar Spectra

    NASA Astrophysics Data System (ADS)

    Dembska, M.; Kijak, J.; Lewandowski, W.

    2012-12-01

    Recently published results (Kijak et al. 2011a) indicated the evidence for a new aspect in radio pulsars spectra. We studied the radio spectrum of PSR B1259-63 in an unique binary with Be star LS 2883 and showed that this pulsar undergoes a spectrum evolution due to the orbital motion. We proposed a qualitative model which explains this evolution. We considered two mechanisms that might influence the observed radio emission: free-free absorption and cyclotron resonance. According to the published results (Kijak et al. 2011b), there were found objects with a new type of pulsar radio spectra, called gigahertz-peaked spectra (GPS) pulsars. Most of them were found to exist in very interesting environments. Therefore, it is suggested that the turnover phenomenon is associated with the environment, rather than being related intrinsically to the radio emission mechanism. Having noticed an apparent resemblance between the B1259-63 spectrum and the GPS, we suggested that the same mechanisms should be responsible for both cases. Thus, we believe that this binary system can hold the clue to the understanding of the gigahertz-peaked spectra of isolated pulsars. Using the same database we constructed spectra for chosen observing days and obtained different types of spectra. Comparing to current classification of pulsar spectra, there occurs a suggestion that the appearance of various spectra shapes, different from a simple power law which is typical for radio pulsars, is possibly caused by environmental conditions around neutron stars.

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

    SciTech Connect

    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.; 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.

  7. Detection and localization of continuous gravitational waves with pulsar timing arrays: the role of pulsar terms

    NASA Astrophysics Data System (ADS)

    Zhu, X.-J.; Wen, L.; Xiong, J.; Xu, Y.; Wang, Y.; Mohanty, S. D.; Hobbs, G.; Manchester, R. N.

    2016-09-01

    A pulsar timing array is a Galactic-scale detector of nanohertz gravitational waves (GWs). Its target signals contain two components: the `Earth term' and the `pulsar term' corresponding to GWs incident on the Earth and pulsar, respectively. In this work we present a Frequentist method for the detection and localization of continuous waves that takes into account the pulsar term and is significantly faster than existing methods. We investigate the role of pulsar terms by comparing a full-signal search with an Earth-term-only search for non-evolving black hole binaries. By applying the method to synthetic data sets, we find that (i) a full-signal search can slightly improve the detection probability (by about five per cent); (ii) sky localization is biased if only Earth terms are searched for and the inclusion of pulsar terms is critical to remove such a bias; (iii) in the case of strong detections (with signal-to-noise ratio ≳30), it may be possible to improve pulsar distance estimation through GW measurements.

  8. Turn-over in pulsar spectra: From young pulsars to millisecond ones

    NASA Astrophysics Data System (ADS)

    Kijak, J.; Lewandowski, W.; Serylak, M.

    2008-02-01

    The evidence for turn-over in young pulsar radio spectra at high frequencies is presented. The frequency at which a spectrum shows the maximum flux density is called the peak frequency. This peak frequency appears to depend on pulsar age and dispersion measure. A possible relation with pulsar age is interesting. Millisecond pulsars, which are very old objects, may show no evidence for spectral turn-over down to 100 MHz. Some studied pulsars with turn-over at high frequencies have been shown to have very interesting interstellar environments. This could suggest that the turn-over phenomenon is associated with the enviromental conditions around the neutron stars, rahter than being related intrinsically with the radio emission mechanism. Although there are no earlier reports of such a connection, a more detailed study on larger sample of pulsars is needed to address this idea more quantitatively. In this context, future observations below 200 MHz using LOFAR will allow us to investigate turn-over in radio pulsar spectra.

  9. The Pulsar Search Collaboratory: Discovery and Timing of Five New Pulsars

    NASA Astrophysics Data System (ADS)

    Rosen, R.; Swiggum, J.; McLaughlin, M. A.; Lorimer, D. R.; Yun, M.; Heatherly, S. A.; Boyles, J.; Lynch, R.; Kondratiev, V. I.; Scoles, S.; Ransom, S. M.; Moniot, M. L.; Cottrill, A.; Weaver, M.; Snider, A.; Thompson, C.; Raycraft, M.; Dudenhoefer, J.; Allphin, L.; Thorley, J.; Meadows, B.; Marchiny, G.; Liska, A.; O'Dwyer, A. M.; Butler, B.; Bloxton, S.; Mabry, H.; Abate, H.; Boothe, J.; Pritt, S.; Alberth, J.; Green, A.; Crowley, R. J.; Agee, A.; Nagley, S.; Sargent, N.; Hinson, E.; Smith, K.; McNeely, R.; Quigley, H.; Pennington, A.; Chen, S.; Maynard, T.; Loope, L.; Bielski, N.; McGough, J. R.; Gural, J. C.; Colvin, S.; Tso, S.; Ewen, Z.; Zhang, M.; Ciccarella, N.; Bukowski, B.; Novotny, C. B.; Gore, J.; Sarver, K.; Johnson, S.; Cunningham, H.; Collins, D.; Gardner, D.; Monteleone, A.; Hall, J.; Schweinhagen, R.; Ayers, J.; Jay, S.; Uosseph, B.; Dunkum, D.; Pal, J.; Dydiw, S.; Sterling, M.; Phan, E.

    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 deg2 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.

  10. Thermal properties of three Fermi pulsars

    NASA Astrophysics Data System (ADS)

    Danilenko, A.; Karpova, A.; Kirichenko, A.; Shibanov, Y.; Shternin, P.; Zharikov, S.; Zyuzin, D.

    2014-07-01

    We analysed thermal properties of the Fermi pulsars J0357+3205, J1741-2054, and J0633+0632 using data from the XMM-Newton and Chandra archives. The X-ray spectra of all three pulsars can be fitted by sum of thermal and power-law components. For J1741-2054, the thermal component is best described by a blackbody model whose normalization suggests that the thermal emission comes from the bulk of the neutron star surface. The effective temperature of 60 eV, which is rather large for a pulsar as old as J1741-2054, makes it similar to the well-studied pulsar B1055-52, one of ``the three musketeers''. The thermal components of PSRs J0357+3205 and J0633+0632 can be equally well described by blackbody or the hydrogen atmosphere models. In the former case the normalizations suggest hot polar cap as thermal emission origin and only upper limits on the neutron stars surface temperatures can be computed. For the hydrogen atmosphere models, the normalizations are in agreement with emission coming from a substantial part of neutron star surface. Thermal properties of the pulsars are confronted with similar data on other isolated neutron stars and predictions of the neutron star cooling theory.

  11. Polarization Properties of Rotation Powered Pulsars

    NASA Technical Reports Server (NTRS)

    Harding Alice K.

    2009-01-01

    Polarization measurements of rotation-powered pulsars and their nebulae have unique diagnostic potential. The polarization position angle of the pulsar wind nebula, as is know for the Crab pulsar, can tell us the orientation of the spin axis. Phase-resolved polarimetry of pulsars has had enormous diagnostic capability at radio and optical wavelengths and could also be a powerful diagnostic in the X-ray range. Measurement of the polarization properties as a function of pulse phase can therefore provide a multidimensional mapping of the pulsar emission. In the 'rotating vector' model, radiation originating near a magnetic pole is expected to show a characteristic S-shaped swing of the position angle vs. pulse phase. In this case it is possible to determine the magnetic inclination and viewing angles. Radiation originating further from the poles or further above the neutron star surface will have a more complex polarization signature, as a result of relativistic effects of aberration and time-of-flight delays and may also cause depolarization of the signal. I will discuss predicted polarization properties of pulsed emission in polar cap models, where radiation originates near the neutron star surface at the magnetic poles, and in slot gap and outer gap models, where radiation originates over a range of altitudes out to the speed-of-light cylinder.

  12. Probing Microstructure in Interstellar Plasma with Pulsars

    NASA Astrophysics Data System (ADS)

    Backer, Donald

    1999-11-01

    Pulsars provide excellent probes of small structure in the interstellar plasma. The list of observable effects includes dispersion, Faraday rotation, diffraction and refraction. Of great interest recently has been episodes of lensing and dual path propagation when the plasma perturbation has just the right focal length for the pulsar-perturber-earth geometry at a given frequency. I will discuss a recent study of the variable dispersion, refraction and diffraction of the millisecond pulsar B1937+21. This is based mainly on daily observations at 327 and 610 MHz with a pulsar monitoring telescope in Green Bank, WV. Further observations at 820 and 1395 MHz allow us to investigate the limits on dispersion measure determination set by diffraction. Length scales in the medium from 10^10 to 10^15 cm are probed. A second study focuses on a rare event in the Crab pulsar where the dispersion measure jumped by 0.1 pc cm-3 within one week and, prior to the jump, a faint and delayed ghost of the pulsed emission was observed. These phenomena can be explained in terms of a plasma wedge crossing the line of sight. The most likely location of this wedge is in the Rayleigh-Taylor unstable interface between the expanding supernova remains and the pre-supernova stellar wind debris.

  13. IS CALVERA A GAMMA-RAY PULSAR?

    SciTech Connect

    Halpern, J. P.

    2011-07-20

    Originally selected as a neutron star (NS) candidate in the ROSAT All-Sky Survey, 1RXS J141256.0+792204 ('Calvera') was discovered to be a 59 ms X-ray pulsar in a pair of XMM-Newton observations by Zane et al. Surprisingly, their claimed detection of this pulsar in Fermi {gamma}-ray data requires no period derivative, severely restricting its dipole magnetic field strength, spin-down luminosity, and distance to small values. This implies that the cooling age of Calvera is much younger than its characteristic spin-down age. If so, it could be a mildly recycled pulsar, or the first 'orphaned' central compact object (CCO). Here we show that the published Fermi ephemeris fails to align the pulse phases of the two X-ray observations with each other, which indicates that the Fermi detection is almost certainly spurious. Analysis of additional Fermi data also does not confirm the {gamma}-ray detection. This leaves the spin-down rate of Calvera less constrained, and its place among the families of NSs uncertain. It could still be either an ordinary pulsar, a mildly recycled pulsar, or an orphaned CCO.

  14. PULSAR WIND NEBULAE WITH THICK TOROIDAL STRUCTURE

    SciTech Connect

    Chevalier, Roger A.; Reynolds, Stephen P. E-mail: reynolds@ncsu.edu

    2011-10-10

    We investigate a class of pulsar wind nebulae that show synchrotron emission from a thick toroidal structure. The best studied such object is the small radio and X-ray nebula around the Vela pulsar, which can be interpreted as the result of interaction of a mildly supersonic inward flow with the recent pulsar wind. Such a flow near the center of a supernova remnant can be produced in a transient phase when the reverse shock reaches the center of the remnant. Other nebulae with a thick toroidal structure are G106.6+2.9 and G76.9+1.0. Their structure contrasts with young pulsar nebulae like the Crab Nebula and 3C 38, which show a more chaotic, filamentary structure in the synchrotron emission. In both situations, a torus-jet structure is present where the pulsar wind passes through a termination shock, indicating the flow is initially toroidal. We suggest that the difference is due to the Rayleigh-Taylor instability that operates when the outer boundary of the nebula is accelerating into freely expanding supernova ejecta. The instability gives rise to mixing in the Crab and related objects, but is not present in the nebulae with thick toroidal regions.

  15. LUMINOSITY EVOLUTION OF GAMMA-RAY PULSARS

    SciTech Connect

    Hirotani, Kouichi

    2013-04-01

    We investigate the electrodynamic structure of a pulsar outer-magnetospheric particle accelerator and the resulting gamma-ray emission. By considering the condition for the accelerator to be self-sustained, we derive how the trans-magnetic-field thickness of the accelerator evolves with the pulsar age. It is found that the thickness is small but increases steadily if the neutron-star envelope is contaminated by sufficient light elements. For such a light element envelope, the gamma-ray luminosity of the accelerator is kept approximately constant as a function of age in the initial 10,000 yr, forming the lower bound of the observed distribution of the gamma-ray luminosity of rotation-powered pulsars. If the envelope consists of only heavy elements, on the other hand, the thickness is greater, but it increases less rapidly than a light element envelope. For such a heavy element envelope, the gamma-ray luminosity decreases relatively rapidly, forming the upper bound of the observed distribution. The gamma-ray luminosity of a general pulsar resides between these two extreme cases, reflecting the envelope composition and the magnetic inclination angle with respect to the rotation axis. The cutoff energy of the primary curvature emission is regulated below several GeV even for young pulsars because the gap thickness, and hence the acceleration electric field, is suppressed by the polarization of the produced pairs.

  16. Gamma-ray Pulsars: Models and Predictions

    NASA Technical Reports Server (NTRS)

    Harding Alice K.; White, Nicholas E. (Technical Monitor)

    2000-01-01

    Pulsed emission from gamma-ray pulsars originates inside the magnetosphere, from radiation by charged particles accelerated near the magnetic poles or in the outer gaps. In polar cap models, the high energy spectrum is cut off by magnetic pair production above an energy that is, dependent on the local magnetic field strength. While most young pulsars with surface fields in the range B = 10(exp 12) - 10(exp 13) G are expected to have high energy cutoffs around several GeV, the gamma-ray spectra of old pulsars having lower surface fields may extend to 50 GeV. Although the gamma-ray emission of older pulsars is weaker, detecting pulsed emission at high energies from nearby sources would be an important confirmation of polar cap models. Outer gap models predict more gradual high-energy turnovers of the primary curvature emission around 10 GeV, but also predict an inverse Compton component extending to TeV energies. Detection of pulsed TeV emission, which would not survive attenuation at the polar caps, is thus an important test of outer gap models. Next-generation gamma-ray telescopes sensitive to GeV-TeV emission will provide critical tests of pulsar acceleration and emission mechanisms.

  17. PULSAR OBSERVATIONS USING THE FIRST STATION OF THE LONG WAVELENGTH ARRAY AND THE LWA PULSAR DATA ARCHIVE

    SciTech Connect

    Stovall, K.; Dowell, J.; Eftekhari, T.; McCrackan, M.; Schinzel, F. K.; Taylor, G. B.; Ray, P. S.; Blythe, J.; Garcia, A.; Lazio, T. J. W.

    2015-08-01

    We present initial pulsar results from the first station of the Long Wavelength Array (LWA1) obtained during the commissioning period of LWA1 and in early science results. We present detections of periodic emission from 44 previously known pulsars, including 3 millisecond pulsars. The effects of the interstellar medium (ISM) on pulsar emission are significantly enhanced at the low frequencies of the LWA1 band (10–88 MHz), making LWA1 a very sensitive instrument for characterizing changes in the dispersion measure (DM) and other effects from the ISM. Pulsars also often have significant evolution in their pulse profile at low frequency and a break in their spectral index. We report DM measurements for 44 pulsars, mean flux density measurements for 36 pulsars, and multi-frequency component spacing and widths for 15 pulsars with more than one profile component. For 27 pulsars, we report spectral index measurements within our frequency range. We also introduce the LWA1 Pulsar Data Archive, which stores reduced data products from LWA1 pulsar observations. Reduced data products for the observations presented here can be found in the archive. Reduced data products from future LWA1 pulsar observations will also be made available through the archive.

  18. Gamma ray emission from radio pulsars

    NASA Technical Reports Server (NTRS)

    Romani, Roger W.

    1994-01-01

    While the proposed research received partial funding under this grant, during the term of support substantial progress was made on the development of a new model for the emission of gamma-rays from isolated rotation-powered pulsars. In phase one of the work, we showed how a modified version of the 'outer gap' model of pulsar emission could reproduce the double peaked profiles seen in CGRO pulsar observations. This work also demonstrated the spectrum of gap radiation varies significantly with position in the magnetosphere, and produced approximate computations of the emission from outer magnetosphere gap zones, including primary curvature radiation, gamma - gamma pair production and synchrotron radiation and inverse Compton scattering by the resulting secondary particles. This work was followed in phase two by a more complete treatment of the geometry of the radiation zone, and improved connections with observations at other wavelengths.

  19. EVIDENCE OF AN ASTEROID ENCOUNTERING A PULSAR

    SciTech Connect

    Brook, P. R.; Karastergiou, A.; Buchner, S.; Roberts, S. J.; Keith, M. J.; Johnston, S.; Shannon, R. M.

    2014-01-10

    Debris disks and asteroid belts are expected to form around young pulsars due to fallback material from their original supernova explosions. Disk material may migrate inward and interact with a pulsar's magnetosphere, causing changes in torque and emission. Long-term monitoring of PSR J0738–4042 reveals both effects. The pulse shape changes multiple times between 1988 and 2012. The torque, inferred via the derivative of the rotational period, changes abruptly from 2005 September. This change is accompanied by an emergent radio component that drifts with respect to the rest of the pulse. No known intrinsic pulsar processes can explain these timing and radio emission signatures. The data lead us to postulate that we are witnessing an encounter with an asteroid or in-falling debris from a disk.

  20. Are there two types of pulsars?

    NASA Astrophysics Data System (ADS)

    Contopoulos, I.

    2016-11-01

    In order to investigate the importance of dissipation in the pulsar magnetosphere, we decided to combine force-free with Aristotelian electrodynamics. We obtain solutions that are ideal (non-dissipative) everywhere except in an equatorial current sheet where Poynting flux from both hemispheres converges and is dissipated into particle acceleration and radiation. We find significant dissipative losses (up to about 50 per cent of the pulsar spin-down luminosity), similar to what is found in global Particle-In-Cell simulations in which particles are provided only on the stellar surface. We conclude that there might indeed exist two types of pulsars, strongly dissipative ones with particle injection only from the stellar surface, and ideal (weakly dissipative) ones with particle injection in the outer magnetosphere and in particular at the Y-point.

  1. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2012-04-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  2. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2012-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  3. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2010-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the eclipse region and the orbital secular evolution).

  4. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2011-10-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  5. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2011-04-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  6. Timing of millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2013-04-01

    Timing of the dozen pulsars discovered by us in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the orbital secular evolution, the eclipse region, and the mechanisms leading to the ejection of matter from the binary system).

  7. Polarimetric Observation of Pulsars with Hexes

    NASA Astrophysics Data System (ADS)

    Xue, M.; Bhat, R.; Tremblay, S.; Ord, S.; Sobey, C.; Kirsten, F.

    2016-07-01

    The MWA VCS pipeline is now reliably generating high time resolution observations of radio pulsars in all four Stokes parameters. Here, we are proposing to test the polarimetric response of and our ability to calibrate the new Hex array currently under construction. These observation will provide data that will be used to study the pulsars themselves (including their emission mechanism and beam geometry), the interstellar medium and towards understanding the Galactic magnetic field. We are proposing a set of observations of three pulsars (J0034-0534, J0437-4715, and J2145-0750) at a wide range of hour angles to characterise the fidelity and stability of the polarimetric solutions with the hexes. The observation would be performed between 170-200 MHz and 140-170 MHz respectively. This project will form part of the PhD program of Mengyao Xue.

  8. A survey for Hα pulsar bow shocks

    SciTech Connect

    Brownsberger, Sasha; Romani, Roger W. E-mail: sashab@stanford.edu

    2014-04-01

    We report on a survey for Hα bow shock emission around nearby γ-detected energetic pulsars. This survey adds three Balmer-dominated neutron star bow shocks to the six previously confirmed examples. In addition to the shock around Fermi pulsar PSR J1741–2054, we now report Hα structures around two additional γ-ray pulsars, PSR J2030+4415 and PSR J1509–5850. These are the first known examples of Hα nebulae with pre-ionization halos. With new measurements, we show that a simple analytic model can account for the angular size and flux of the bow shocks' apices. The latter, in particular, provides a new pulsar probe and indicates large moments of inertia and smaller distances than previously assumed in several cases. In particular, we show that the re-measured PSR J0437–4715 shock flux implies I = (1.7 ± 0.2) × 10{sup 45}/(f {sub HI}sin i) g cm{sup 2}. We also derive a distance d ≈ 0.72 kpc for the γ-ray only pulsar PSR J2030+4415 and revised distances for PSRs J1959+2048 (1.4 kpc) and J2555+6535 (∼1 kpc), smaller than the conventional DM-estimated values. Finally, we report upper limits for 94 additional LAT pulsars. An estimate of the survey sensitivity indicates that for a warm neutral medium filling factor φ{sub WNM} ∼ 0.3 there should be a total of approximately nine Hα bow shocks in our LAT-targeted survey; given that seven such objects are now known, a much larger φ{sub WNM} seems problematic.

  9. Modification of band gap in surface layer in Cd 1-xZn xTe by YAG:Nd +3 laser radiation

    NASA Astrophysics Data System (ADS)

    Medvid, Artur; Fedorenko, Leonid L.; Korbutjak, Dmytro V.; Kryluk, Sergiy G.; Yusupov, Mikola M.; Mychko, Aleksandr

    2007-02-01

    A mechanism of formation of graded band-gap based on Thermogradient Effect (TGE) is proposed in Cd 1-xZn xTe at irradiation by second harmonic of a Q-switched YAG:Nd laser. According to the effect, the interstitial atoms of Cd (Cd i) in Cd 1-xZn xTe move along the temperature gradient while the Cd vacancies (V Cd) and Zn atoms - in the opposite direction, into the bulk of the semiconductor where temperature is lower. Photoluminescence (PL) spectra studied at 5 K show that concentration of Zn atoms increases due to aggregation of VCd with Zn after laser irradiation. Formation of a graded band-gap in Cd 1-xZn xTe crystal at irradiation by second harmonica of YAG:Nd laser by is shown to be possible.

  10. Large scale pulsar surveys, new pulsar discoveries, and the observability of pulsar beams strongly bent by the Sag. A* black hole

    NASA Astrophysics Data System (ADS)

    Stovall, Kevin

    Pulsars are useful tools for a large range of topics including but not limited to the detection of gravitational waves; tests of theories of gravity; population studies of pulsars, neutron stars, and binary systems; and analysis of Galactic structure. In the case of detections of gravitational waves, large numbers of extremely fast pulsars with periods of a few milliseconds distributed across a large number of angular separations are needed. In the case of population and Galactic structure studies, large numbers of pulsars distributed throughout the Galaxy are necessary. In order to find pulsars in the exotic systems useful for tests of theories of gravity, large number of pulsar discoveries are necessary in order to find these rare objects. As all of these efforts require the discovery of large numbers of pulsars, a significant effort has been made over the past few years, and will continue into the foreseeable future, to detect many more new radio pulsars through large scale pulsar surveys. The surveys related to this work include the Pulsar Arecibo L-Band Feed Array, the Green Bank 350MHz Drift Scan Survey, the Arecibo 327MHz Drift Scan Survey (AO327), and the Green Bank North Celestial Cap (GBNCC) survey. Data analysis from each of these surveys has resulted or will result in millions of pulsar candidates to be combed through, in some way, in order to find new radio pulsars. Here we discuss these surveys and the data analysis pipelines for two of them (AO327 and GBNCC). We also introduce a web based software system called ARCC Explorer, which enables researchers of varying levels, including high school and undergraduate students, to assist in the discovery process. In addition, we give discovery or timing solutions for 93 new pulsars directly discovered as a result of this work. One particularly interesting, but not yet detected, pulsar system is the pulsar-black hole system. Attempts have been made (and are still ongoing) to detect pulsars orbiting the black

  11. The Ages, Speeds and Offspring of Pulsars

    NASA Astrophysics Data System (ADS)

    Hansen, Bradley Miles Stougaard

    1996-01-01

    We investigate the cooling of low mass white dwarfs with helium cores. We construct a detailed numerical model using the most modern input physics, including our own calculations of low temperature hydrogen opacities. We use our models to constrain the ages of binary millisecond pulsars from the optical observations of their white dwarf companions. We use this to place limits on the initial spin periods, magnetic field decay times and accretion histories of the millisecond pulsars. Our models can also be used along with observations of spectroscopic gravities and radial velocities to place interesting constraints on the neutron star equation of state. We provide grids of temperature and luminosity as a function of age for various white dwarf masses and surface compositions to facilitate future analyses. We have investigated the effect of the pulsar wind on the atmospheric composition of binary companions. The spallation of atmospheric helium to hydrogen increases the cooling age of the white dwarf. We find that all white dwarf companions in binaries with orbital period < 300 days should cool as DA (hydrogen surface layer) white dwarfs, irrespective of their original hydrogen content. We investigate the effect of various wind compositions and note that, if almost all the hydrogen on the surface of a pulsar companion is the result of spallation of an ionic wind, then the D/H ratio is large. We investigate the processes by which planets might form around a millisecond pulsar such as PSR B1257 + 12. We study the evolution of accretion disks of different mass, angular momentum and composition, corresponding to various proposed formation scenarios. We find that most formation scenarios require a high efficiency of conversion of metal-rich material into planets if they are to produce the observed parameters of the 1257 + 12 planetary system. We have studied the distribution of pulsar proper motions in the light of the recent analysis of Lyne & Lorimer (1994). Using a

  12. Pulsar glitches: the crust is not enough.

    PubMed

    Andersson, N; Glampedakis, K; Ho, W C G; Espinoza, C M

    2012-12-14

    Pulsar glitches are traditionally viewed as a manifestation of vortex dynamics associated with a neutron superfluid reservoir confined to the inner crust of the star. In this Letter we show that the nondissipative entrainment coupling between the neutron superfluid and the nuclear lattice leads to a less mobile crust superfluid, effectively reducing the moment of inertia associated with the angular momentum reservoir. Combining the latest observational data for prolific glitching pulsars with theoretical results for the crust entrainment, we find that the required superfluid reservoir exceeds that available in the crust. This challenges our understanding of the glitch phenomenon, and we discuss possible resolutions to the problem.

  13. Interstellar scattering of the Vela pulsar

    NASA Technical Reports Server (NTRS)

    Backer, D. C.

    1974-01-01

    The frequency dependence of the parameters of interstellar scattering between 837 and 8085 MHz for the Vela pulsar are consistent with thin-screen models of strong scattering. The magnitudes of the parameters indicate an anomalous turbulence along the path when they are compared with results for other pulsars with comparable column densities of free electrons in the line of sight. This anomaly is due presumably to the Gum Nebula. The decorrelation frequency, appropriately defined, is related to the pulse broadening time by 2 pi as predicted theoretically.

  14. THE CROSS SPECTRAL TIME LAG EVOLUTION ALONG BRANCHES IN XTE J1701-462

    SciTech Connect

    Li Zhaosheng; Chen Li; Bu Qingcui; Wang Dehua; Qu Jinlu E-mail: chenli@bnu.edu.cn

    2013-04-20

    We investigate the cross spectrum of XTE J1701-462 in various types of neutron star low-mass X-ray binary subclasses during its 2006-2007 outburst. We analyze the relation between the time lags and temporal variabilities. We find that the hard time lags accompany horizontal branch oscillations (HBOs) and the soft time lags dominate the noise in the low frequency range 0.1-10 Hz on HB. In the Cyg-like phase, the time lags decrease on the middle normal branch (NB) from HB/NB vertex to NB/FB vertex, whereas the time lags are roughly invariant in the Sco-like source. We discuss the fact that the Compton upscattering by the corona introduces the soft lag in low-frequency noise. We suggest that the variation of the Comptonization component from the disk emission leads to the HBOs' time lag evolutions along the Z tracks. We also report the rms amplitude spectrum and phase lag spectrum for the normal branch oscillation (NBO). A {approx}160 Degree-Sign phase lag is found. We find that the rms amplitudes of both the Cyg-like and the Sco-like NBOs linearly increase with the photon energy in low energy bands, and drop in the highest energy band.

  15. Transient relativistic ejections and stationary core in XTE J1752-223

    NASA Astrophysics Data System (ADS)

    Yang, J.; Paragi, Z.; Corbel, S.; Gurvits, L. I.; Campbell, R. M.; Brocksopp, C.

    2011-11-01

    The Galactic X-ray transient XTE J1752-223 was shown to have properties of black hole binary candidates. As reported in our previous paper, we identified transient and decelerating ejecta in multi-epoch Very Long Baseline Interferometry (VLBI) observations with the European VLBI Network (EVN) and the NRAO Very Long Baseline Array (VLBA). Here we present new EVN and VLBA data in which a new transient ejection event and later a stationary component are identified. The latter is interpreted as a reappearance of the radio core/compact jet during the transition from soft to hard X-ray state. This component appears to be highly variable in brightness although effects of tropospheric instabilities might play a role too. We also re-analyse the earlier VLBI data and find that the transient ejecta closer to the core position has significantly higher proper motion, further strengthening the case for strongly decelerating ejecta on the scale of several hundred milliarcsecond, never observed in X-ray binaries before. Although the distance of the source is not well constrained, it is clear that these ejectas are at least mildly relativistic at the early stages. Moreover, we show the large scale environment of the transient from the Westerbork synthesis array data recorded in parallel during the EVN run.

  16. Observational Signatures of Black Holes: Spectral and Temporal Features of XTE J1550-564

    NASA Technical Reports Server (NTRS)

    Titarchuk, Lev; Shrader, C. R.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    The theoretical predictions of the converging inflow, or Bulk-Motion Comptonization model are discussed and some predictions are compared to X- and gamma-ray observations of the high-soft state of Galactic black hole candidate XTE J1550+564. The approx. 10(exp 2)-Hz QPO phenomenon tends to be detected in the high-state at times when the bolometric luminosity surges and the hard-powerlaw spectral component is dominant. Furthermore, the power in these features increases with energy. We offer interpretation of this phenomenon, as oscillations of the innermost part of the accretion disk, which in turn supplies the seed photons for the converging inflow where the hard power-law is formed through Bulk Motion Comptonization (BMC). We further argue that the noted lack of coherence between intensity variations of the high-soft-state low and high energy bands is a natural consequence of our model, and that a natural explanation for the observed hard and soft lag phenomenon is offered. In addition, we address some criticisms of the BMC model supporting our claims with observational results.

  17. Relativistically Skewed Iron Emission and Disk Reflection in Galactic Microquasar XTE J1748-288

    NASA Technical Reports Server (NTRS)

    Miller, J. M.; Fox, D. W.; DiMatteo, T.; Wijnands, R.; Belloni, T.; Kouveliotou, C.; Lewin, W. H. G.

    2000-01-01

    We report evidence for an Fe K-alpha fluorescence line feature in the Very High, High, and Low state X-ray spectra of the galactic microquasar XTE JI748-288 during its June 1998 outburst. Spectral analyses were made on observations spread across the outburst, gathered with the Rossi X-ray Timing Explorer. Gaussian line. disk emission line, relativistic disk emission line, and disk reflection models are fit to the data. In the Very High State, the line profile is strongly redshifted and consistent with emission from the innermost radius of a maximally rotating Kerr black hole, 1.235 R(sub g). The line profile is less redshifted in the High State, but increasingly prominent. In the Low State, the line profile is very strong and centered af approx. 6.7 keV; disk line emission models constrain the inner edge of the disk to fluctuate between approx.20 and approx.59 R(sub g). We trace the disk reflection fraction across the full outburst of this source, and find well-constrained fractions below those observed in AGN in the Very High and High States, but consistent with other galactic sources in the Low State. We discuss the possible implications for black hole X-ray binary system dynamics and accretion flow geometry.

  18. On the Nature of XTE J0421+560/CI Cam

    NASA Technical Reports Server (NTRS)

    Belloni, T.; vandenAncker, M.; Dieters, S.; Fender, R.; Fox, D. W.; Kommers, J. M.; Lewin, W. H. G.; VanParadijs, J.

    1999-01-01

    We present the results of the analysis of RXTE, BATSE and optical/IR data of the 1998 outburst of the x-ray transient system XTE J0421+650. The x-ray outburst shows a very fast decay initial e-folding time approximately 0.5 days, slowing down to about 2.3 days). The X ray spectrum in the 2-25 keV band is thermal, softening considerably during decay. Intrinsic absorption is observed, also strongly variable. A strong iron line at around 6.7 keV is observed. No fast time variability is observed (<0.1 rms in the 1-4906 Hz band at peak). The analysis of optical/IR data suggest that the secondary is a b[e] star and place the system at a distance of about 2 kpc. At this distance the 2-25 keV luminosity is about 5 x 10(exp 37) erg/seconds. We compare the properties of this system with those of the Be/NS LMC transient A 0538-66 and suggest that CI cam is of a similar nature. The presence of strong radio emission during outburst indicates that the compact object could be a black hole.

  19. Highly efficient functional GexPb1-xTe based thermoelectric alloys.

    PubMed

    Gelbstein, Yaniv; Davidow, Joseph

    2014-10-07

    Methods for enhancement of the direct thermal to electrical energy conversion efficiency, upon development of advanced thermoelectric materials, are constantly investigated mainly for efficient implementation of thermoelectric devices in automotive vehicles, for converting the waste heat generated in such engines into useful electrical power and thereby reduction of the fuel consumption and CO2 emission levels. It was recently shown that GeTe based compounds and specifically GeTe-PbTe rich alloys are efficient p-type thermoelectric compositions. In the current research, Bi2Te3 doping and PbTe alloying effects in GexPb1-xTe alloys, subjected to phase separation reactions, were investigated for identifying the phase separation potential for enhancement of the thermoelectric properties beyond a pure alloying effect. All of the investigated compositions exhibit maximal dimensionless figure of merit, ZT, values beyond 1, with the extraordinary value of 2.1 found for the 5% Bi2Te3 doped-Ge0.87Pb0.13Te composition, considered as among the highest ever reported.

  20. XTE J1550-564: INTEGRAL Observations of a Failed Outburst

    NASA Technical Reports Server (NTRS)

    Sturner, S. J.; Shrader, C. R.

    2004-01-01

    The well known black-hole X-ray binary transient XTE J1550-564 underwent an outburst during the spring of 2003 which was substantially underluminous in comparison to previous periods of peak activity in that source. In addition, our analysis shows that it apparently remained in the hard spectral state over the duration of that outburst. This is again in sharp contrast to major out-bursts of that source in 1998/1999 during which it exhibited an irregular light curve, multiple state changes and collimated outflows. This leads us to classify it as a failed outburst. We present the results of our study of the spring 2003 event including light curves based on observations from both INTEGRAL and RXTE. In addition, we studied the evolution of the high-energy 3-300 keV continuum spectrum using data obtained with three main instruments on INTEGRAL. These spectra are consistent with typical low-hard-state thermal Comptonization emission. We also consider the 2003 event in the context of a multi-source, multi-event period-peak luminosity diagram in which it is a clear outlyer. We then consider the possibility that the 2003 event was due to a discrete accretion event rather than a limit-cycle instability. In that context, apply model fitting to derive the timescale for viscous propagation in the disk, and infer some physical characteristics.

  1. PULSAR BINARY BIRTHRATES WITH SPIN-OPENING ANGLE CORRELATIONS

    SciTech Connect

    O'Shaughnessy, Richard; Kim, Chunglee E-mail: ckim@astro.lu.s

    2010-05-20

    One ingredient in an empirical birthrate estimate for pulsar binaries is the fraction of sky subtended by the pulsar beam: the pulsar beaming fraction. This fraction depends on both the pulsar's opening angle and the misalignment angle between its spin and magnetic axes. The current estimates for pulsar binary birthrates are based on an average value of beaming fractions for only two pulsars, i.e., PSRs B1913+16 and B1534+12. In this paper, we revisit the observed pulsar binaries to examine the sensitivity of birthrate predictions to different assumptions regarding opening angle and alignment. Based on empirical estimates for the relative likelihood of different beam half-opening angles and misalignment angles between the pulsar rotation and magnetic axes, we calculate an effective beaming correction factor, f{sub b,eff}, whose reciprocal is equivalent to the average fraction of all randomly selected pulsars that point toward us. For those pulsars without any direct beam geometry constraints, we find that f{sub b,eff} is likely to be smaller than 6, a canonically adopted value when calculating birthrates of Galactic pulsar binaries. We calculate f{sub b,eff} for PSRs J0737-3039A and J1141-6545, applying the currently available constraints for their beam geometry. As in previous estimates of the posterior probability density function P(R) for pulsar binary birthrates R, PSRs J0737-3039A and J1141-6545 still significantly contribute to, if not dominate, the Galactic birthrate of tight pulsar-neutron star (NS) and pulsar-white dwarf (WD) binaries, respectively. Our median posterior present-day birthrate predictions for tight PSR-NS binaries, wide PSR-NS binaries, and tight PSR-WD binaries given a preferred pulsar population model and beaming geometry are 89 Myr{sup -1}, 0.5 Myr{sup -1}, and 34 Myr{sup -1}, respectively. For long-lived PSR-NS binaries, these estimates include a weak (x1.6) correction for slowly decaying star formation in the galactic disk. For pulsars

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

    NASA Technical Reports Server (NTRS)

    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

  3. Chandra Examines a Quadrillion-Volt Pulsar

    NASA Astrophysics Data System (ADS)

    2001-09-01

    The high-voltage environment of one of the most energetic and strongly magnetized pulsars known has been surveyed by NASA's Chandra X-ray Observatory. A team of astronomers found a powerful jet of high-energy particles extending over a distance of 20 light years and bright arcs believed to be due to particles of matter and anti-matter generated by the pulsar. The team of US, Canadian, and Japanese scientists pointed Chandra at the rapidly spinning neutron star B1509-58, located 19,000 light years away in the constellation of Circinus, for over five hours. These results were announced at the "Two Years of Science with Chandra" symposium in Washington, DC. "Jets and arcs on this vast scale have never been seen in any other pulsar," said Bryan Gaensler of the Smithsonian Astrophysical Observatory. "The spectacular images we have obtained of this source are letting us test theories as to how pulsars unleash so much energy." The features seen with Chandra give the scientists insight into the process by which voltages of more than 7000 trillion volts are created around rotating neutron stars (the dense remnants of supernova explosions) and how these extreme voltages affect their environment. B1509-58 is of particular interest because it has a much stronger magnetic field than the Crab Nebula pulsar, which exhibits similar features on a much smaller scale. The general picture emerging from these results is that high-energy particles of matter and antimatter are streaming away from the neutron star along its poles and near its equator. The particles leaving the poles produce the jets; astronomers speculate that only one side of the jet is apparent in B1509-58, indicating that this one side is beamed in our direction, while the other is rushing away. "Until this observation, no one knew for sure whether such tremendous voltages and energy outputs were a trademark of all pulsars, or if the Crab was an oddball," said Vicky Kaspi of McGill University in Montreal. "Now thanks

  4. Growth and characterization of CdTe, Mn(x)Cd(1-x)Te, Zn(x)Cd(1-x)Te, and CdSe(y)Te(1-y) crystals

    NASA Astrophysics Data System (ADS)

    Lay, K. Y.; Giles-Taylor, N. C.; Schetzina, J. F.; Bachmann, K. J.

    1986-05-01

    Structures and growth characteristics of crystals based on the Cd-Te lattice, which are potentially useful in infrared radiation detectors, are described. Single crystals of CdTe, Mn(x)Cd(1-x)Te, and CdSe(y)Te(1-y) have been grown by the vertical Bridgman method and those of Zn(x)Cd(1-l)Te by zone leveling. Photoluminescence (PL) spectra were used to determine the quality and uniformity of composition. From the probing of small areas, allowed by this PL characterization technique, the uniform incorporation of Mn, Zn, and Se into the CdTe lattice was determined.

  5. Growth and characterization of CdTe, Mn(x)Cd(1-x)Te, Zn(x)Cd(1-x)Te, and CdSe(y)Te(1-y) crystals

    SciTech Connect

    Lay, K.Y.; Giles-Taylor, N.C.; Schetzina, J.F.; Bachmann, K.J.

    1986-05-01

    Structures and growth characteristics of crystals based on the Cd-Te lattice, which are potentially useful in infrared radiation detectors, are described. Single crystals of CdTe, Mn(x)Cd(1-x)Te, and CdSe(y)Te(1-y) have been grown by the vertical Bridgman method and those of Zn(x)Cd(1-l)Te by zone leveling. Photoluminescence (PL) spectra were used to determine the quality and uniformity of composition. From the probing of small areas, allowed by this PL characterization technique, the uniform incorporation of Mn, Zn, and Se into the CdTe lattice was determined. 15 references.

  6. A High Braking Index for a Pulsar

    NASA Astrophysics Data System (ADS)

    Archibald, R. F.; Gotthelf, E. V.; Ferdman, R. D.; Kaspi, V. M.; Guillot, S.; Harrison, F. A.; Keane, E. F.; Pivovaroff, M. J.; Stern, D.; Tendulkar, S. P.; Tomsick, J. A.

    2016-03-01

    We present a phase-coherent timing solution for PSR J1640-4631, a young 206 ms pulsar using X-ray timing observations taken with NuSTAR. Over this timing campaign, we have measured the braking index of PSR J1640-4631 to be n = 3.15 ± 0.03. Using a series of simulations, we argue that this unusually high braking index is not due to timing noise, but is intrinsic to the pulsar's spin-down. We cannot, however, rule out contamination due to an unseen glitch recovery, although the recovery timescale would have to be longer than most yet observed. If this braking index is eventually proven to be stable, it demonstrates that pulsar braking indices greater than three are allowed in nature; hence, other physical mechanisms such as mass or magnetic quadrupoles are important in pulsar spin-down. We also present a 3σ upper limit on the pulsed flux at 1.4 GHz of 0.018 mJy.

  7. Pulsars at the Center of the Galaxy

    NASA Astrophysics Data System (ADS)

    Majid, Walid

    2016-07-01

    Over the past few years, a number of groups using data from NASA's space-borne Fermi LAT instrument have identified excess gamma-ray flux toward the inner 1º of the Galactic Center (GC), with an even larger significant excess within 0.2º degrees. At present there are two leading candidates for this excess: dark matter annihilation and a population of unresolved millisecond pulsars (MSPs). We are currently developing dedicated instrumentation to carry out a sensitive search for the pulsars in this region of the galaxy using a newly developed front end and receiver on a Deep Space Network large diameter antenna in Australia. In this presentation, we will provide an overview of the challenges encountered with pulsar searches at the GC region and a summary of previous and ongoing efforts to survey this region with radio telescopes. We will also provide preliminary results from our recent observations of the GC region at 2 and 8 GHz and will conclude with prospects for detection of perhaps hundreds of pulsars in this region with new generations of radio telescopes now under construction.

  8. Pulsars at the Center of the Galaxy

    NASA Astrophysics Data System (ADS)

    Majid, Walid A.; Prince, Thomas A.

    2016-06-01

    Over the past few years, a number of groups using data from NASA’s space-borne Fermi LAT instrument have identified excess gamma-ray flux toward the inner degree of the Galactic Center (GC), with an even larger significant excess within 0.2 degrees. At present there are two leading candidates for this excess: dark matter annihilation and a population of unresolved millisecond pulsars (MSPs). We are currently developing dedicated instrumentation to carry out a sensitive search for the pulsars in this region of the galaxy using a newly developed front end and receiver on a Deep Space Network large diameter antenna in Australia. In this presentation, we will provide an overview of the challenges encountered with pulsar searches at the GC region and a summary of previous and ongoing efforts to survey this region with radio telescopes. We will also provide preliminary results from our recent observations of the GC region at 2 and 8 GHz and will conclude with prospects for detection of perhaps hundreds of pulsars in this region with new generations of radio telescopes now under construction.

  9. Pulsars at the Center of the Galaxy

    NASA Astrophysics Data System (ADS)

    Majid, Walid A.

    2016-04-01

    Over the past few years, a number of groups using data from NASA’s space-borne Fermi LAT instrument have identified excess gamma-ray flux toward the inner few degrees of the Galactic Center (GC), with an even larger significant excess within 1 degree of this region. At present there are two leading candidates for this excess: dark matter annihilation and a population of unresolved millisecond pulsars (MSPs). We are currently developing dedicated instrumentation to carry out a sensitive search for the pulsars in this region of the galaxy using a newly developed front end and receiver on a Deep Space Network large diameter antenna in Australia. In this presentation, we will provide an overview of the challenges encountered with pulsar searches at the GC region and a summary of previous and ongoing efforts to survey this region with radio telescopes. We will also provide preliminary results from our recent observations of the GC region at 2 and 8 GHz and will conclude with prospects for detection of perhaps hundreds of pulsars in this region with new generations of radio telescopes now under construction.

  10. On some electrodynamic properties of binary pulsars

    NASA Astrophysics Data System (ADS)

    Sironi, Lorenzo

    2006-07-01

    The main purpose of my thesis is to examine some electrodynamic properties of binary pulsars, trying to understand the peculiar physical processes that can happen in their magnetospheres; the ultimate aim is to discuss if such systems can be the source of the observed flux of cosmic rays between the knee and the ankle, since the mechanisms of acceleration for the cosmic rays in this range of energies are still unknown. Attention around binary pulsars has arisen after the recent discovery (December 2003) of the first double neutron star system in which both the stars are visible as pulsars (PSR J0737-3039); the inspection of the physical features of this binary pulsar has led to some intriguing possibilities up to now unexplored. In this thesis I will first of all review what is already known about the main properties of this binary system. I will describe in particular the possibility to go further in the verification of the predictions of general relativity with the so-called post-Keplerian parameters; I will discuss the possibility of studying the optical properties of the magnetospheres, since the inclination angle of the orbit is nearly 90° and some orbital phases show an eclipse of the light from one pulsar due to absorption by the magnetosphere of the companion; I will rapidly summarize how the discovery of that binary pulsar can enlarge our knowledge about the origin and evolution of double neutron star systems; lastly, I will examine the increase in the estimate of the Galactic double neutron star merger rate due to the discovery of PSR J0737-3039. I will then summarize the current knowledge about the magnetosphere of a single pulsar. After describing the Gold-Pacini model for the energy loss of the oblique rotator (in which the magnetic and rotational axes are not parallel), I will discuss the Goldreich-Julian model for the aligned axisymmetric rotator in the force-free approximation in which the inertial and gravitational forces are neglected with

  11. Multiwavelength Studies of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Slane, Patrick O.

    2010-03-01

    The extended nebulae formed as pulsar winds expand into their surroundings provide information about the composition of the winds, the injection history from the host pulsar, and the material into which the nebulae are expanding. Observations from across the electromagnetic spectrum provide constraints on the evolution of the nebulae, the density and composition of the surrounding ejecta, the geometry of the central engines, and the long-term fate of the energetic particles produced in these systems. High-energy observations, in particular, reveal the presence of jets and wind termination shocks, time-varying compact emission structures, shocked supernova ejecta, and emission from late-phase nebulae that are extremely faint in other bands. Here I provide a broad overview of the structure of pulsar wind nebulae, with specific examples from observations extending from the radio band to very high energy gamma-rays that demonstrate our ability to constrain the history and ultimate fate of the energy released in the spin-down of young pulsars.

  12. Recently Discovered Pulsars and Unidentified Egret Sources

    NASA Astrophysics Data System (ADS)

    Torres, Diego F.; Butt, Yousaf M.; Camilo, Fernando

    2001-10-01

    We present a correlative study between all unidentified EGRET sources at low Galactic latitudes and the newly discovered pulsars in the released portion of the Parkes multibeam radio survey. We note 14 positional coincidences: eight of these are ``Vela-like'' pulsars with relatively small periods, small characteristic ages, and high spin-down luminosities. Three of these coincidences have been investigated by D'Amico et al. and Camilo et al. Among the others, we argue that PSR J1015-5719 may plausibly generate part of the high-energy radiation observed from 3EG J1014-5705. Three additional interesting cases are 3EG J1410-6147, either of PSRs J1412-6145 or J1413-6141 if the pulsars are at the estimated distance of the coincident SNR G312.4-0.4, and 3EG J1639-4702/PSR J1637-4642. The remaining positional coincidences between the EGRET sources and the newly discovered pulsars are almost certainly spurious.

  13. Observations of the Eclipsing Millisecond Pulsar

    NASA Astrophysics Data System (ADS)

    Bookbinder, Jay

    1990-12-01

    FRUCHTER et al. (1988a) HAVE RECENTLY DISCOVERED a 1.6 MSEC PULSAR (PSR 1957+20) IN A 9.2 HOUR ECLIPSING BINARY SYSTEM. THE UNUSUAL BEHAVIOR OF THE DISPERSION MEASURE AS A FUNCTION OF ORBITAL PHASE, AND THE DISAPPEARANCE OF THE PULSAR SIGNAL FOR 50 MINUTES DURING EACH ORBIT, IMPLIES THAT THE ECLIPSES ARE DUE TO A PULSAR-INDUCED WIND FLOWING OFF OF THE COMPANION. THE OPTICAL COUNTERPART IS A 21ST MAGNITUDE OBJECT WHICH VARIES IN INTENSITY OVER THE BINARY PERIOD; ACCURATE GROUND-BASED OBSERVATIONS ARE PREVENTED BY THE PROXIMITY (0.7") OF A 20TH MAGNITUDE K DWARF. WE PROPOSE TO OBSERVE THE OPTICAL COUNTERPART IN A TWO-PART STUDY. FIRST, THE WF/PC WILL PROVIDE ACCURATE MULTICOLOR PHOTOMETRY, ENABLING US TO DETERMINE UNCONTAMINATED MAGNITUDES AND COLORS BOTH AT MAXIMUM (ANTI-ECLIPSE) AS WELL AS AT MINIMUM (ECLIPSE). SECOND, WE PROPOSE TO OBSERVE THE EXPECTED UV LINE EMISSION WITH FOS, ALLOWING FOR AN INTIAL DETERMINATION OF THE TEMPERATURE AND DENSITY STRUCTURE AND ABUNDANCES OF THE WIND THAT IS BEING ABLATED FROM THE COMPANION. STUDY OF THIS UNIQUE SYSTEM HOLDS ENORMOUS POTENTIAL FOR THE UNDERSTANDING OF THE RADIATION FIELD OF A MILLISECOND PULSAR AND THE EVOLUTION OF LMXRBs AND MSPs IN GENERAL. WE EXPECT THESE OBSERVATIONS TO PLACE VERY SIGNIFICANT CONTRAINTS ON MODELS OF THIS UNIQUE OBJECT.

  14. A HIGH BRAKING INDEX FOR A PULSAR

    SciTech Connect

    Archibald, R. F.; Ferdman, R. D.; Kaspi, V. M.; Tendulkar, S. P.; Gotthelf, E. V.; Guillot, S.; Harrison, F. A.; Keane, E. F.; Pivovaroff, M. J.; Stern, D.; Tomsick, J. A.

    2016-03-01

    We present a phase-coherent timing solution for PSR J1640–4631, a young 206 ms pulsar using X-ray timing observations taken with NuSTAR. Over this timing campaign, we have measured the braking index of PSR J1640–4631 to be n = 3.15 ± 0.03. Using a series of simulations, we argue that this unusually high braking index is not due to timing noise, but is intrinsic to the pulsar's spin-down. We cannot, however, rule out contamination due to an unseen glitch recovery, although the recovery timescale would have to be longer than most yet observed. If this braking index is eventually proven to be stable, it demonstrates that pulsar braking indices greater than three are allowed in nature; hence, other physical mechanisms such as mass or magnetic quadrupoles are important in pulsar spin-down. We also present a 3σ upper limit on the pulsed flux at 1.4 GHz of 0.018 mJy.

  15. Pulsar J1823-3021A

    NASA Video Gallery

    This video shows the on and off state of gamma rays from pulsar J1823-3021A as seen by Fermi's Large Area Telescope (LAT). The object pulses 183.8 times a second and has a spin period of 5.44 milli...

  16. Generation of radio waves in pulsars.

    PubMed

    Smith, F G

    1970-12-05

    Pulsars generate radio waves by an unknown process which gives the highest volume emissivity known in astrophysics. The radiation forms a beam the width and polarization of which are independent of frequency. This article assembles the observational facts which any theory of emission must explain.

  17. Chandra Results on Pulsars and Plerions

    NASA Astrophysics Data System (ADS)

    Pavlov, G. G.

    2000-10-01

    I will overview the results of imaging, spectral and timing analysis of isolated neutron stars observed in Chandra Cycle 1, including the young Vela pulsar and its X-ray plerion, the middle-aged pulsar B1055--52, the millisecond pulsar J0437--4715, the radio-silent isolated neutron stars in the PKS 1209--51/52, Puppis A and Cas A supernova remnants. Among the results are the fine spatial structure and spectrum of the Vela compact nebula, the multicomponent light curve and spectrum of the Vela pulsar, discovery of the 424 ms period of 1E 1207--52, the phase-dependent spectrum and energy-dependent pulse profile of PSR B1055-52, the lack of X-ray emission from the bow-shock nebula of PSR J0437--4715. The work was partially supported by SAO grants GO0-1012X, GO0-1126X and GO0-1131A.

  18. Thermal analysis of specific heat measurements in glassy Se80-xTe20Sbx alloys in glass transition region

    NASA Astrophysics Data System (ADS)

    Saraswat, S.; Mehta, N.; Sharma, S. D.

    2016-01-01

    In the present report, we have done specific heat measurements in glassy Se80-xTe20Sbx (0 ≤ x ≤ 15) alloys in glass transition region. Differential scanning calorimetry (DSC) technique is used for this purpose. We have observed a tremendously huge increase in the specific heat (Cp) values at the glass transition temperature. The thermal analysis shows that the values of Cp below glass transition temperature and the difference of Cp values before and after glass transition (∆Cp) are highly composition-dependent.

  19. DETECTING MASSIVE GRAVITONS USING PULSAR TIMING ARRAYS

    SciTech Connect

    Lee, Kejia; Kramer, Michael; Jenet, Fredrick A.; Price, Richard H.; Wex, Norbert

    2010-10-20

    At the limit of weak static fields, general relativity becomes Newtonian gravity with a potential field that falls off as inverse distance rather than a theory of Yukawa-type fields with a finite range. General relativity also predicts that the speed of disturbances of its waves is c, the vacuum light speed, and is non-dispersive. For these reasons, the graviton, the boson for general relativity, can be considered to be massless. Massive gravitons, however, are features of some alternatives to general relativity. This has motivated experiments and observations that, so far, have been consistent with the zero-mass graviton of general relativity, but further tests will be valuable. A basis for new tests may be the high sensitivity gravitational wave (GW) experiments that are now being performed and the higher sensitivity experiments that are being planned. In these experiments, it should be feasible to detect low levels of dispersion due to non-zero graviton mass. One of the most promising techniques for such a detection may be the pulsar timing program that is sensitive to nano-Hertz GWs. Here, we present some details of such a detection scheme. The pulsar timing response to a GW background with the massive graviton is calculated, and the algorithm to detect the massive graviton is presented. We conclude that, with 90% probability, massless gravitons can be distinguished from gravitons heavier than 3 x 10{sup -22} eV (Compton wavelength {lambda}{sub g} = 4.1 x 10{sup 12} km), if bi-weekly observation of 60 pulsars is performed for 5 years with a pulsar rms timing accuracy of 100 ns. If 60 pulsars are observed for 10 years with the same accuracy, the detectable graviton mass is reduced to 5 x 10{sup -23} eV ({lambda}{sub g} = 2.5 x 10{sup 13} km); for 5 year observations of 100 or 300 pulsars, the sensitivity is respectively 2.5 x 10{sup -22} ({lambda}{sub g} = 5.0 x 10{sup 12} km) and 10{sup -22} eV ({lambda}{sub g} = 1.2 x 10{sup 13} km). Finally, a 10 year

  20. High-Energy Emission From Millisecond Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Usov, Vladimir V.; Muslimov, Alex G.

    2004-01-01

    The X-ray and gamma-ray spectrum of rotation-powered millisecond pulsars is investigated in a model for acceleration and pair cascades on open field lines above the polar caps. Although these pulsars have low surface magnetic fields, their short periods allow them to have large magnetospheric potential drops, but the majority do not produce sufficient pairs to completely screen the accelerating electric field. In these sources, the primary and secondary electrons continue to accelerate to high altitude and their Lorentz factors are limited by curvature and synchrotron radiation reaction. The accelerating particles maintain high Lorentz factors and undergo cyclotron resonant absorption of radio emission, that produces and maintains a large pitch angle, resulting in a strong synchrotron component. The resulting spectra consist of several distinct components: curvature radiation from primary electrons dominating from 1 - 100 GeV, synchrotron radiation from primary and secondary electrons dominating up to about 100 MeV, and much weaker inverse-Compton radiation from primary electrons a t 0.1 - 1 TeV. We find that the relative size of these components depends on pulsar period, period derivative, and neutron star mass and radius with the level of the synchrotron component also depending sensitively on the radio emission properties. This model is successful in describing the observed X-ray and gamma-ray spectrum of PSR J0218+4232 as synchrotron radiation, peaking around 100 MeV and extending up to a turnover around several GeV. The predicted curvature radiation components from a number of millisecond pulsars, as well as the collective emission from the millisecond pulsars in globular clusters, should be detectable with AGILE and GLAST. We also discuss a hidden population of X-ray-quiet and radio-quiet millisecond pulsars which have evolved below the pair death line, some of which may be detectable by telescopes sensitive above 1 GeV. Subject headings: pulsars: general

  1. CHANDRA PULSAR SURVEY (ChaPS)

    SciTech Connect

    Kargaltsev, Oleg; Durant, Martin; Pavlov, George G.; Garmire, Gordon

    2012-08-01

    Taking advantage of the high sensitivity of the Chandra X-ray Observatory's (CXO) Advanced CCD Imaging Spectrometer, we have conducted a snapshot survey of pulsars previously undetected in X-rays. We detected 12 pulsars and established deep flux limits for 11 pulsars. Using these new results, we revisit the relationship between the X-ray luminosity, L{sup psr}{sub X}, and spin-down power, E-dot . We find that the obtained limits further increase the extremely large spread in the non-thermal X-ray efficiencies, {eta}{sup psr}{sub X} = L{sup psr}{sub X}/ E-dot , with some of them being now below 10{sup -5}. Such a spread cannot be explained by poorly known distances or by beaming of pulsar radiation. We also find evidence of a break in the dependence of L{sup psr}{sub X} on E-dot , such that pulsars become more X-ray efficient at E-dot {approx}<10{sup 34}-10{sup 35} erg s{sup -1}. We examine the relationship between the {gamma}-ray luminosity, L{sup psr}{sub {gamma}}, and E-dot , which exhibits a smaller scatter compared to that in X-rays. This confirms that the very large spread in the X-ray efficiencies cannot be explained just by the beaming because the {gamma}-ray emission is generally expected to be beamed stronger than the X-ray emission. Intriguingly, there is also an indication of a break in the L{sup psr}{sub {gamma}} ( E-dot ) dependence at E-dot {approx}10{sup 35} erg s{sup -1}, with lower- E-dot pulsars becoming less {gamma}-ray efficient. We also examine the distance-independent L{sup psr}{sub {gamma}}/L{sup psr}{sub X} ratio as a function of E-dot for a sample of {gamma}-ray pulsars observed by CXO and find that it peaks at E-dot {approx}10{sup 35} erg s{sup -1}, showing that the breaks cannot originate from poorly measured distances. We discuss the implications of our findings for existing models of magnetospheric emission and venues for further exploration.

  2. Multi-wavelength analysis of young pulsars: an overview.

    NASA Astrophysics Data System (ADS)

    Maritz, J. M.; Meintjes, P. J.; Buchner, S. J.

    Young pulsars emit a broad spectrum of radiation that range from radio to gamma ray energies. These pulsars are considered as rotation powered pulsars that spin rapidly and are strongly magnetized. Following the discovery of pulsars nearly four decades ago, the population of known pulsars already reached a number of roughly two thousand. This known population of pulsars includes both millisecond and normal pulsars that were discovered by several telescopes. We analyze both HartRAO radio data and Fermi gamma ray data of the Vela pulsar. We also explore a proposed method of probing the electron column density of the instellar gas through analyzing the gamma ray diffuse data associated with the Fermi two-year observation. This paper serves as an overview of gamma ray and radio timing analysis of bright young pulsars with respect to the use of open source timing analysis tools (Tempo2, Psrchive, Enrico and the Fermi tools). We reason that the multi-wavelength picture of pulsars can help clarify questions regarding the origin of pulsed radiation emission mechanisms in several energy bands, but that radio observations will prove adequate for timing noise analysis, given the accurate and long radio data sets. The process of identifying gravitational waves in timing data, rests on gaining a deeper insight into the timing noise phenomena.

  3. Properties and geometry of radio pulsar emission

    NASA Astrophysics Data System (ADS)

    Smits, Johannes Martinus

    2006-10-01

    This thesis consists of a number of studies on the radio emission of pulsars. The central topics are polarisation and multi frequency observations, which both lead to important information on the geometry of the emission. The first chapter introduces different aspects of pulsars that are related to the research that has been done in this thesis. In particular it deals with different aspects concerning the geometry of pulsar emission. Chapter 2 is about the nature of the radio emission. It shows the result of an attempt to confirm and expand on work that has been published by Jenet et al. (2001) on the detection of coherence in pulsar radiation. From an analysis of high time resolution observations, we found that the detection of coherence is consistent with the effects of interstellar scintillation. In chapter 3 a study is carried out on the orthogonal polarisation mode behaviour as a function of frequency of 18 pulsars. By making the assumption that the radiation consists of two 100% polarised completely orthogonal superposed modes, both modes could be separated In chapter 4 PSR B0031-07 is studied at two frequencies using two observations that were carried out simultaneously. It is shown that from the three known drift modes, only one drift mode is seen at high frequency. Based on this result we suggest a geometrical model in which different modes are emitted in concentric rings around the magnetic axis, with each mode having a different radius. The fifth chapter follows the suggestions made in chapter 4 to create a geometrical model of PSR B0031-07 for two of the drift modes. The results can be used to limit the possible geometries of PSR B0031-07. The final chapter consists of documentation of software that was written in C and utilised for this thesis for handling and analysing data files in the EPN format

  4. OSCILLATION-DRIVEN MAGNETOSPHERIC ACTIVITY IN PULSARS

    SciTech Connect

    Lin, Meng-Xiang; Xu, Ren-Xin; Zhang, Bing E-mail: r.x.xu@pku.edu.cn

    2015-02-01

    We study the magnetospheric activity in the polar cap region of pulsars under stellar oscillations. The toroidal oscillation of the star propagates into the magnetosphere, which provides additional voltage due to unipolar induction, changes Goldreich-Julian charge density from the traditional value due to rotation, and hence influences particle acceleration. We present a general solution of the effect of oscillations within the framework of the inner vacuum gap model and consider three different inner gap modes controlled by curvature radiation, inverse Compton scattering, and two-photon annihilation, respectively. With different pulsar parameters and oscillation amplitudes, one of three modes would play a dominant role in defining the gap properties. When the amplitude of oscillation exceeds a critical value, mode changing occurs. Oscillations also lead to a change of the size of the polar cap. As applications, we show the inner gap properties under oscillations in both normal pulsars and anomalous X-ray pulsars/soft gamma-ray repeaters (AXPs/SGRs). We interpret the onset of radio emission after glitches/flares in AXPs/SGRs as due to oscillation-driven magnetic activities in these objects, within the framework of both the magnetar model and the solid quark star model. Within the magnetar model, radio activation may be caused by the enlargement of the effective polar cap angle and the radio emission beam due to oscillation, whereas within the solid quark star angle, it may be caused by activation of the pulsar inner gap from below the radio emission death line due to an oscillation-induced voltage enhancement. The model can also explain the glitch-induced radio profile change observed in PSR J1119–6127.

  5. Implication of the Observable Spectral Cutoff Energy Evolution in XTE J1550-564

    NASA Technical Reports Server (NTRS)

    Titarchuk, Lev; Shaposhnikov, Nikolai

    2010-01-01

    The physical mechanisms responsible for production of the non-thermal emission in accreting black holes should be imprinted in the observational appearances of the power law tails in the X-ray spectra from these objects. Variety of spectral states observed from galactic black hole binaries by it Rossi X-ray Timing Explorer (RXTE) allow examination of the photon upscattering under different accretion regimes. We revisit of RXTE data collected from the black hole X-ray binary XTE J1550-564 during two periods of X-ray activity in 1998 and 2000 focusing on the behavior of the high energy cutoff of the power law part of the spectrum. For the 1998 outburst the Iran- sition from the low-hard state to the intermediate state was accompanied by a gradual decrease in the cutoff energy which then showed a sharp reversal to a clear increasing trend during the further evolution towards the very high and high-soft states. However, the 2000 outburst showed only the decreasing part of this pattern. Notably, the photon indexes corresponding to the cutoff increase for the 1998 event are much higher than the index values reached during the 2000 rise transition. We attribute this difference in the cutoff' energy behav- for to the different partial contributions of the thermal and non-thermal (bulk motion) Comptonization in photon upscattering. Namely, during the 1998 event the higher accretion rate presumably provided more cooling to the Comptonizing media and thus reducing the effectiveness of the thermal upscattering process. Under these conditions the bulk motion takes a leading role in boosting the input soft photons. Monte Carlo simulations of the The physical mechanisms responsible for production of the non-thermal emission in accreting black holes should be imprinted in the observational apperances of the power law tails in the X-ray spectra from these objects. Variety of spectral states observed from galactic black hole binaries by it Rossi X-ray Timing Explorer (RXTE) allow

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

    NASA Astrophysics Data System (ADS)

    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.

  7. Application of the Gaussian mixture model in pulsar astronomy - pulsar classification and candidates ranking for the Fermi 2FGL catalogue

    NASA Astrophysics Data System (ADS)

    Lee, K. J.; Guillemot, L.; Yue, Y. L.; Kramer, M.; Champion, D. J.

    2012-08-01

    Machine learning, algorithms designed to extract empirical knowledge from data, can be used to classify data, which is one of the most common tasks in observational astronomy. In this paper, we focus on Bayesian data classification algorithms using the Gaussian mixture model and show two applications in pulsar astronomy. After reviewing the Gaussian mixture model and the related expectation-maximization algorithm, we present a data classification method using the Neyman-Pearson test. To demonstrate the method, we apply the algorithm to two classification problems. First, it is applied to the well-known period-period derivative diagram, where we find that the pulsar distribution can be modelled with six Gaussian clusters, with two clusters for millisecond pulsars (recycled pulsars) and the rest for normal pulsars. From this distribution, we derive an empirical definition for millisecond pulsars as {P\\dot;}/{10-17}≤3.23({P}/{100ms})-2.34. The two millisecond pulsar clusters may have different evolutionary origins, since the companion stars to these pulsars in the two clusters show different chemical compositions. Four clusters are found for normal pulsars. Possible implications for these clusters are also discussed. Our second example is to calculate the likelihood of unidentified Fermi point sources being pulsars and rank them accordingly. In the ranked point-source list, the top 5 per cent sources contain 50 per cent known pulsars, the top 50 per cent contain 99 per cent known pulsars and no known active galaxy (the other major population) appears in the top 6 per cent. Such a ranked list can be used to help the future follow-up observations for finding pulsars in unidentified Fermi point sources.

  8. High-energy pulsar models: Developments and new questions

    NASA Astrophysics Data System (ADS)

    Venter, C.; Harding, A. K.

    2014-03-01

    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 γ-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 γ-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 our

  9. High-Energy Pulsar Models: Developments and New Questions

    NASA Technical Reports Server (NTRS)

    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

  10. IMPLICATION OF THE OBSERVED SPECTRAL CUTOFF ENERGY EVOLUTION IN XTE J1550-564

    SciTech Connect

    Titarchuk, Lev; Shaposhnikov, Nikolai E-mail: lev.titarchuk@nrl.navy.mi

    2010-12-01

    The physical mechanisms responsible for the production of non-thermal emission in accreting black holes (BHs) should be imprinted in the observational appearances of the power-law tails in the X-ray spectra from these objects. Phenomenology of different spectral states exhibited by galactic BH binaries allows us to establish the physics of the photon upscattering under different accretion regimes. We revisit the data collected by the Rossi X-ray Timing Explorer from the BH X-ray binary XTE J1550-564 during two periods of X-ray activity in 1998 and 2000 focusing on the behavior of the high-energy cutoff of the power-law part of the spectrum. For the 1998 outburst, the transition from the low-hard state to the intermediate state was accompanied by a gradual decrease in the cutoff energy. This was followed by an extended minimum which then showed an abrupt reversal to a clear increasing trend as the source evolved to the very high and high-soft states. The 2000 outburst showed only the decreasing and extended minimum portions of this pattern. We attribute this difference in the cutoff energy behavior to the different partial contributions of the thermal and non-thermal (bulk motion) Comptonization. Namely, during the 1998 event the higher accretion rate presumably provided more cooling to the Comptonizing media and thus reducing the effectiveness of the thermal upscattering process. Under these conditions, the bulk motion takes a leading role in boosting the input soft photons. Recent Monte Carlo simulations by Laurent and Titarchuk strongly support this scenario.

  11. Einstein@Home Finds an Elusive Pulsar

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    Since the release of the second Fermi-LAT catalog in 2012, astronomers have been hunting for 3FGL J1906.6+0720, a gamma-ray source whose association couldn't be identified. Now, personal-computer time volunteered through the Einstein@Home project has resulted in the discovery of a pulsar that has been hiding from observers for years. A Blind Search: Identifying sources detected by Fermi-LAT can be tricky: the instrument's sky resolution is limited, so the position of the source can be hard to pinpoint. The gamma-ray source 3FGL J1906.6+0720 appeared in both the second and third Fermi-LAT source catalogs, but even after years of searching, no associated radio or X-ray source had been found. A team of researchers, led by Colin Clark of the Max Planck Institute for Gravitational Physics, suspected that the source might be a gamma-ray pulsar. To confirm this, however, they needed to detect pulsed emission — something inherently difficult given the low photon count and the uncertain position of the source. The team conducted a blind search for pulsations coming from the general direction of the gamma-ray source. Two things were needed for this search: clever data analysis and a lot of computing power. The data analysis algorithm was designed to be adaptive: it searched a 4-dimensional parameter space that included a safety margin, allowing the algorithm to wander if the source was at the edge of the parameter space. The computing power was contributed by tens of thousands of personal computers volunteered by participants in the Einstein@Home project, making much shorter work out of a search that would have required dozens of years on a single laptop. The sky region around the newly discovered pulsar. The dotted ellipse shows the 3FGL catalog 95% confidence region for the source. The data analysis algorithm was designed to search an area 50% larger (given by the dashed ellipse), but it was allowed to “walk away” within the gray shaded region if the source seemed to

  12. Long-Term Timing of Globular Cluster Pulsars

    NASA Astrophysics Data System (ADS)

    Roi Smith, Sergio; Lynch, Ryan S.

    2017-01-01

    Pulsar timing is a powerful astrophysical tool that allows us to study both pulsars and their environment. Timing models provide information about the pulsar itself, including mass, position, and orbital parameters for pulsars in binary systems. Timing models also provide information about the pulsar’s neighborhood and about the interstellar medium (ISM) between the pulsar and the Earth. We present the results of timing two millisecond globular cluster pulsars over five years, as well as steps involved in preparing the data for use in the timing model. Data was obtained using the Robert C. Byrd Green Bank Telescope (GBT) observing at 1.5 GHz between 2011 and 2015. Here, a description of the data processing procedure is given, and timing results including dispersion measure and higher order rotational period derivatives are discussed.

  13. Candidates for Pulsars with Gigahertz-Peaked Spectra

    NASA Astrophysics Data System (ADS)

    Tarczewski, L.; Kijak, J.; Lewandowski, W.

    2012-12-01

    Kijak et al. (2011) provided a definite evidence for a new type of pulsar radio spectra. These spectra show the maximum flux above 1 GHz and their energy decreases below 1 GHz, producing a positive spectral index at lower frequencies. They called these objects the gigahertz-peaked spectra (GPS) pulsars. We study a spectrum of radio pulsars and try to find pulsars with the turn-over effect at high frequencies. We created a database of candidates for pulsars with GPS effect using Maron et al. (2000) and ATNF database (Manchester et al. 2005), and also using recent papers where flux measurements were published (for example Bates et al. 2011). As a result a set of 22 candidates for pulsars with GPS was found.

  14. A periodically active pulsar giving insight into magnetospheric physics.

    PubMed

    Kramer, M; Lyne, A G; O'Brien, J T; Jordan, C A; Lorimer, D R

    2006-04-28

    PSR B1931+24 (J1933+2421) behaves as an ordinary isolated radio pulsar during active phases that are 5 to 10 days long. However, when the radio emission ceases, it switches off in less than 10 seconds and remains undetectable for the next 25 to 35 days, then switches on again. This pattern repeats quasi-periodically. The origin of this behavior is unclear. Even more remarkably, the pulsar rotation slows down 50% faster when it is on than when it is off. This indicates a massive increase in magnetospheric currents when the pulsar switches on, proving that pulsar wind plays a substantial role in pulsar spin-down. This allows us, for the first time, to estimate the magnetospheric currents in a pulsar magnetosphere during the occurrence of radio emission.

  15. Switched magnetospheric regulation of pulsar spin-down.

    PubMed

    Lyne, Andrew; Hobbs, George; Kramer, Michael; Stairs, Ingrid; Stappers, Ben

    2010-07-23

    Pulsars are famed for their rotational clocklike stability and their highly repeatable pulse shapes. However, it has long been known that there are unexplained deviations (often termed timing noise) from the rate at which we predict these clocks should run. We show that timing behavior often results from two different spin-down rates. Pulsars switch abruptly between these states, often quasi-periodically, leading to the observed spin-down patterns. We show that for six pulsars the timing noise is correlated with changes in the pulse shape. Many pulsar phenomena, including mode changing, nulling, intermittency, pulse-shape variability, and timing noise, are therefore linked and are caused by changes in the pulsar's magnetosphere. We consider the possibility that high-precision monitoring of pulse profiles could lead to the formation of highly stable pulsar clocks.

  16. High Magnetic Field Pulsars and Magnetars: A Unified Picture.

    PubMed

    Zhang; Harding

    2000-05-20

    We propose a unified picture of high magnetic field radio pulsars and magnetars by arguing that they are all rotating high-field neutron stars but that their magnetic axes have different orientations with respect to their rotation axes. In strong magnetic fields where photon splitting suppresses pair creation near the surface, the high-field pulsars can have active inner accelerators while the anomalous X-ray pulsars cannot. This can account for the very different observed emission characteristics of the anomalous X-ray pulsar 1E 2259+586 and the high-field radio pulsar PSR J1814-1744. A predicted consequence of this picture is that radio pulsars having surface magnetic fields greater than about 2x1014 G should not exist.

  17. The Multipupil Fiber Spectroscopy of the Crab-pulsar Neighbourhood

    NASA Astrophysics Data System (ADS)

    Zharikov, S.; Shibanov, Y.; Koptsevich, A.; Afanas'ev, V.; Dodonov, S.

    2001-03-01

    We present the spatially resolved optical spectroscopy of the 12 arcsec × 24 arcsec Crab pulsar neighbourhood in the range λ λ 4600 - 5700 Å made with the Multipupil Fiber Spectrograph at the 6 m telescope of the SAO RAS. The spectra exhibit blue- and red-shifted strong [O III] and weaker Hβ and He II emission lines with the shifts and intensities varying with the position in the field. They hint the presence of a cone-like rotating structure centered at the pulsar position and oriented along the symmetry axis of the compact, torus-like pulsar nebula seen in optical continuum and soft X-rays. The kinematic structure is most likely associated with the pulsar nebula. If so, the compact nebular rotates counter-clockwise with respect to its symmetry axis, or the pulsar spin axis, and the estimated rotational velocity within cylindrical radii of several thousand AU from the pulsar is ~ 2000-3000 km/s.

  18. Vela-like Pulsars: A Bridge Between Young and Old

    NASA Technical Reports Server (NTRS)

    Finley, John P.

    1997-01-01

    This grant was in support of a guest observation using the ASCA satellite of the young, spin-powered pulsar PSR B1706-44. The pulsar is interesting for several reasons: 1) it is young and shares many similar characteristics with the Vela pulsar, 2) it is one of a few pulsars which has been detected by the EGRET detector aboard the CGRO satellite, and 3) it is one of the confirmed sources of TeV gamma-rays discovered with ground based telescopes. The goals of the observation were to search for pulsations in the X-ray domain and to study the near stellar environment to determine if the pulsar is embedded within a compact nebula as in the case of the Vela pulsar.

  19. Cd{sub 1−x}Mn{sub x}Te ultrasmall quantum dots growth in a silicate glass matrix by the fusion method

    SciTech Connect

    Dantas, Noelio Oliveira; Lima Fernandes, Guilherme de; Almeida Silva, Anielle Christine; Baffa, Oswaldo; Gómez, Jorge Antônio

    2014-09-29

    In this study, we synthesized Cd{sub 1−x}Mn{sub x}Te ultrasmall quantum dots (USQDs) in SiO{sub 2}-Na{sub 2}CO{sub 3}-Al{sub 2}O{sub 3}-B{sub 2}O{sub 3} glass system using the fusion method. Growth of these Cd{sub 1−x}Mn{sub x}Te USQDs was confirmed by optical absorption, atomic force microscopy (AFM), magnetic force microscopy (MFM), scanning transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR) measurements. The blueshift of absorption transition with increasing manganese concentration gives evidence of incorporation of manganese ions (Mn{sup 2+}) in CdTe USQDs. AFM, TEM, and MFM confirmed, respectively, the formation of high quality Cd{sub 1−x}Mn{sub x}Te USQDs with uniformly distributed size and magnetic phases. Furthermore, EPR spectra showed six lines associated to the S = 5/2 spin half-filled d-state, characteristic of Mn{sup 2+}, and confirmed that Mn{sup 2+} are located in the sites core and surface of the CdTe USQD. Therefore, synthesis of high quality Cd{sub 1−x}Mn{sub x}Te USQDs may allow the control of optical and magnetic properties.

  20. In-Flight Observations of Long-Term Single-Event Effect (SEE) Performance on X-ray Timing Explorer (XTE) Solid-state Recorders (SSRs)

    NASA Technical Reports Server (NTRS)

    Poivey, Christian; Gee, George; LaBel, Kenneth A.; Barth, Janet L.

    2004-01-01

    We present multi-year Single Event Upset (SEU) flight data on Solid State Recorder (SSR) memories for the X-ray Timing Explorer (XTE) NASA mission. Actual SEU rates are compared to the predicted rates based on ground test data and environment models.

  1. Application of the Nonballistic Model to the Black Hole Candidate XTE J1752-223 and the Quasar NRAO 150

    NASA Astrophysics Data System (ADS)

    Zheng, T. Y.; Gong, B. P.

    2017-02-01

    Optical and radio observations of the black hole candidate XTE J1752-223 have exhibited a slightly curved motion of the jet components, which is associated with its radio light curve. In addition, observations of the quasar NRAO 150 have revealed a core–jet structure wobbling with a high angular speed. In this paper, the phenomena displayed in these two different sources are interpreted as the precession of a bent jet. In such a scenario, hot spots reproduced at different separations from the core precess on the same precession cone, in which different components correspond to different propagation times to the observer. By fitting the kinematics of the components of XTE J1752-223 and its light curve with a curved pattern of precession period 314 days, we find that the propagation time can make an earlier event appear later, and the jet axis can oscillate during its precession. Simulating the quasar NRAO 150 with the same scenario reveals that the knots at larger separation from the core precess at a slower speed than those closer in. A possible mechanism relating to the cooling time of a component is proposed. These three new results are of importance in understanding the physics underlying the curved jet as well as the activity of the central engine of different black hole systems.

  2. High-Frequency Quasi-Periodic Oscillations in the 2000 Outburst of the Galactic Microquasar XTE J1550-564

    NASA Technical Reports Server (NTRS)

    Miller, J. M.; Wijnands, R.; Homan, J.; Belloni, T.; Pooley, D.; Kouveliotou, C.; vanderKlis, M.; Lewin, W. H. G.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    We present an analysis of the high-frequency timing properties of the April-May 2000 outburst of the black hole candidate and Galactic microquasar XTE J1550-564, measured with the Rossi X-ray Timing Explorer, The rapid X-ray variability we measure is consistent with the source being in either the "very high" or "intermediate" canonical black hole state. A strong (5-8% RMS) quasi-periodic oscillation (QPO) is found between 249-278 Hz; this may represent the first recurrence of the same high-frequency QPO in subsequent outbursts of a transient black hole candidate. We also present possible evidence for a lower-frequency QPO at approximately 187 Hz, also reported previously and likely present simultaneously with the higher-frequency QPO. We discuss these findings within the context of the 1998 outburst of XTE J1550-564, and comment on implications for models of QPOs, accretion flows, and black hole spin.

  3. Prediction of an arc-tunable Weyl Fermion metallic state in Mo(x)W(1-x)Te2.

    PubMed

    Chang, Tay-Rong; Xu, Su-Yang; Chang, Guoqing; Lee, Chi-Cheng; Huang, Shin-Ming; Wang, BaoKai; Bian, Guang; Zheng, Hao; Sanchez, Daniel S; Belopolski, Ilya; Alidoust, Nasser; Neupane, Madhab; Bansil, Arun; Jeng, Horng-Tay; Lin, Hsin; Zahid Hasan, M

    2016-02-15

    A Weyl semimetal is a new state of matter that hosts Weyl fermions as emergent quasiparticles. The Weyl fermions correspond to isolated points of bulk band degeneracy, Weyl nodes, which are connected only through the crystal's boundary by exotic Fermi arcs. The length of the Fermi arc gives a measure of the topological strength, because the only way to destroy the Weyl nodes is to annihilate them in pairs in the reciprocal space. To date, Weyl semimetals are only realized in the TaAs class. Here, we propose a tunable Weyl state in Mo(x)W(1-x)Te2 where Weyl nodes are formed by touching points between metallic pockets. We show that the Fermi arc length can be changed as a function of Mo concentration, thus tuning the topological strength. Our results provide an experimentally feasible route to realizing Weyl physics in the layered compound Mo(x)W(1-x)Te2, where non-saturating magneto-resistance and pressure-driven superconductivity have been observed.

  4. Limits on neutron Lorentz violation from pulsar timing

    SciTech Connect

    Altschul, Brett

    2007-01-15

    Pulsars are the most accurate naturally occurring clocks, and data about them can be used to set bounds on neutron-sector Lorentz violations. If SO(3) rotation symmetry is completely broken for neutrons, then pulsars' rotation speeds will vary periodically. Pulsar timing data limits the relevant Lorentz-violating coefficients to be smaller than 1.7x10{sup -8} at at least 90% confidence.

  5. On magnetic pair production above fast pulsar polar caps

    NASA Technical Reports Server (NTRS)

    An, S.

    1985-01-01

    Magnetic pair production is one of high-energy electromagnetic conversion processes important to the development of pair-photon cascades in pulsars. On the basis of current polar cap models, the properties of magnetic pair production in fast pulsars are discussed. Suppose there is a roughly dipole magnetic field at the stellar surface, the author estimate the effects on non-zero curvature of magnetic field lines upon curvature radiation from primary particles and pair production rate near the surface of pulsars.

  6. Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2012-01-01

    Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. I will review acceleration and gamma-ray emission from the pulsar polar cap and slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting and population synthesis.

  7. Binary and Millisecond Pulsars at the New Millennium.

    PubMed

    Lorimer, Duncan R

    2001-01-01

    We review the properties and applications of binary and millisecond 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 1300. There are now 56 binary and millisecond pulsars in the Galactic disk and a further 47 in globular clusters. This review is concerned primarily with the results and spin-offs from these surveys which are of particular interest to the relativity community.

  8. Timing analysis for 20 millisecond pulsars in the Parkes Pulsar Timing Array

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    We present timing models for 20 millisecond pulsars in the Parkes Pulsar Timing Array. The precision of the parameter measurements in these models has been improved over earlier results by using longer data sets and modelling the non-stationary noise. We describe a new noise modelling procedure and demonstrate its effectiveness using simulated data. Our methodology includes the addition of annual dispersion measure (DM) variations to the timing models of some pulsars. We present the first significant parallax measurements for PSRs J1024-0719, J1045-4509, J1600-3053, J1603-7202, and J1730-2304, as well as the first significant measurements of some post-Keplerian orbital parameters in six binary pulsars, caused by kinematic effects. Improved Shapiro delay measurements have resulted in much improved pulsar mass measurements, particularly for PSRs J0437-4715 and J1909-3744 with Mp = 1.44 ± 0.07 and 1.47 ± 0.03 M⊙, respectively. The improved orbital period-derivative measurement for PSR J0437-4715 results in a derived distance measurement at the 0.16 per cent level of precision, D = 156.79 ± 0.25 pc, one of the most fractionally precise distance measurements of any star to date.

  9. Pulsar gamma-rays: Spectra luminosities and efficiencies

    NASA Technical Reports Server (NTRS)

    Harding, A. K.

    1980-01-01

    The general characteristics of pulsar gamma ray spectra are presented for a model where the gamma rays are produced by curvature radiation from energetic particles above the polar cap and attenuated by pair production. The shape of the spectrum is found to depend on pulsar period, magnetic field strength, and primary particle energy. By a comparison of numerically calculated spectra with the observed spectra of the Crab and Vela pulsars, it is determined that primary particles must be accelerated to energies of about 3 x 10 to the 7th power mc sq. A genaral formula for pulsar gamma ray luminosity is determined and is found to depend on period and field strength.

  10. Acoustooptical pulsar processor: application of frequency scale calibration

    NASA Astrophysics Data System (ADS)

    Esepkina, Nelli A.; Lavrov, Aleksandr P.; Molodyakov, Sergey A.; Oreshko, Vasiliy V.

    2007-02-01

    The acoustooptical processor (AOP) is based on an acoustooptical spectrum analyzer with a CCD photodetector operating in a special pipeline operational mode (shift-and-add mode), which allows spectral components of the input signal to be added with a controlled time delay immediately in the CCD photodetector. The proposed AOP was successfully used on an RT-64 radio telescope (Kalyazin Radio Astronomy Observatory FIAN) for the observation of pulsars at 1.4 GHz in a bandwidth of 45 MHz. The frequency scale calibration allows increasing accuracy measurement of time of arrival radioemission pulsar. Experimental results of frequency scale calibration and pulsars profiles for a pulsar PSR 1937+21 are submitted.

  11. Observing peculiar γ-ray pulsars with AGILE

    NASA Astrophysics Data System (ADS)

    Pilia, M.; Pellizzoni, A.

    2011-08-01

    The AGILE γ-ray satellite provides large sky exposure levels (>=109 cm2 s per year on the Galactic Plane) with sensitivity peaking at E ~100 MeV where the bulk of pulsar energy output is typically released. Its ~1 μs absolute time tagging capability makes it perfectly suited for the study of γ-ray pulsars. AGILE collected a large number of γ-ray photons from EGRET pulsars (>=40,000 pulsed counts for Vela) in two years of observations unveiling new interesting features at sub-millisecond level in the pulsars' high-energy light-curves, γ-ray emission from pulsar glitches and Pulsar Wind Nebulae. AGILE detected about 20 nearby and energetic pulsars with good confidence through timing and/or spatial analysis. Among the newcomers we find pulsars with very high rotational energy losses, such as the remarkable PSR B1509-58 with a magnetic field in excess of 1013 Gauss, and PSR J2229+6114 providing a reliable identification for the previously unidentified EGRET source 3EG2227+6122. Moreover, the powerful millisecond pulsar B1821-24, in the globular cluster M28, is detected during a fraction of the observations.

  12. MULTIWAVELENGTH CONSTRAINTS ON PULSAR POPULATIONS IN THE GALACTIC CENTER

    SciTech Connect

    Wharton, R. S.; Chatterjee, S.; Cordes, J. M.; Deneva, J. S.; Lazio, T. J. W.

    2012-07-10

    The detection of radio pulsars within the central few parsecs of the Galaxy would provide a unique probe of the gravitational and magneto-ionic environments in the Galactic center (GC) and, if close enough to Sgr A*, precise tests of general relativity in the strong-field regime. While it is difficult to find pulsars at radio wavelengths because of interstellar scattering, the payoff from detailed timing of pulsars in the GC warrants a concerted effort. To motivate pulsar surveys and help define search parameters for them, we constrain the pulsar number and spatial distribution using a wide range of multiwavelength measurements. These include the five known radio pulsars within 15' of Sgr A*, non-detections in high-frequency pulsar surveys of the central parsec, radio and gamma-ray measurements of diffuse emission, a catalog of radio point sources from an imaging survey, infrared observations of massive star populations in the central few parsecs, candidate pulsar wind nebulae in the inner 20 pc, and estimates of the core-collapse supernova rate based on X-ray measurements. We find that under current observational constraints, the inner parsec of the Galaxy could harbor as many as {approx}10{sup 3} active radio pulsars that are beamed toward Earth. Such a large population would distort the low-frequency measurements of both the intrinsic spectrum of Sgr A* and the free-free absorption along the line of sight of Sgr A*.

  13. Characterization of a Precision Pulsar Timing Gravitational Wave Detector

    NASA Astrophysics Data System (ADS)

    Lam, Michael T.

    2017-01-01

    We aim to construct a Galactic-scale detector comprised of an array of pulsars distributed across the sky in an effort to detect low-frequency (nanohertz) gravitational waves. Even without a detection, observations of pulsar timing arrays have allowed us to begin to place impactful astrophysical constraints on dynamical processes occurring during galaxy mergers. Understanding the detector is necessary for improving our sensitivity to gravitational waves and making a detection. Therefore, our goal is to characterize the entire propagation path through the pulsar timing array detector. To do so, we must understand: what intrinsic noise processes occur at the pulsar, what effects the interstellar medium has on pulsed radio emission, and what errors we introduce when measuring the incident electromagnetic radiation at our observatories.In this work, we observed of one of the most spin-stable objects known for 24 hours to understand the fundamental limits of precision pulsar timing. We investigated the effect of non-simultaneous, multi-frequency sampling of pulsar dispersion measures on timing and analyzed the cause of deterministic and stochastic temporal variations seen in dispersion measure time series. We analyzed errors in pulse arrival times and determined the white noise budget for pulsars on the timescale of a single observation. Finally, we measured the excess noise beyond the white noise model in pulsar timing residuals and incorporated our results into a global model over all pulsar populations to improve excess noise scaling relations.

  14. Pulsar searches in nearby dwarf spheroidal galaxies

    NASA Astrophysics Data System (ADS)

    Rubio-Herrera, Eduardo; Maccarone, Thomas

    2013-03-01

    We have been undertaking a comprehensive survey for pulsars and fast radio transients in the dwarf spheroidal satellite galaxies of the Milky Way using the Green Bank Radio Telescope operating at a central frequency of 350 MHz. Our search pipeline allows the detection of periodical signals and single dispersed pulses and it is optimized to search for millisecond radio pulsars. Here we present preliminary results of the searches we have conducted in the Ursa Minoris, Draco and Leo I dwarf spheroidal satellite galaxies. Our searches have revealed no periodic signals but a few unconfirmed millisecond single pulses at various dispersion measures, possibly related to neutron stars. Detecting neutron stars in these systems can potentially help to test the existence of haloes of dark matter surrounding these systems as predicted by Dehnen & King (2006).

  15. Crab pulsar timing 1982-87

    NASA Astrophysics Data System (ADS)

    Lyne, A. G.; Pritchard, R. S.; Smith, F. G.

    1988-08-01

    Observations of the arrival times of pulses from the pulsar in the Crab Nebula over a six-year interval are presented. The data are intended to permit the investigation of the interior of the neutron star through the study of glitches and timing noise and to provide an ephemeris for high-energy observations. The first and second frequency derivatives provide a value for the braking index of n = 2.509 + or - 0.001, which is consistent with previous observations. The third frequency derivative can now be determined over an 18-yr span and is as expected for this braking index. The predominant deviations from a simple slow-down model form a sinusoid with a period of 20 months, attributable to an oscillation of the bulk of the neutron superfluid in the pulsar. One conspicuous glitch occurred in August, 1986 and the subsequent recovery was studied from only one hour after the event.

  16. Mildly Recycled Pulsars at High-Energies

    NASA Astrophysics Data System (ADS)

    Pellizzoni, A.

    2011-08-01

    Mildly recyled pulsars (MRP), conventionally defined as neutron star having spin period in the 20-100 ms range and surface magnetic field <1011 Gauss, probably rise from binary systems (disrupted or not) with an intermediate or an high mass companion. Despite their relatively low spin-down energies compared to the ``fully'' recycled millisecond pulsars (arising from common low mass X-ray binaries), nearby MRPs can be detected by deep X-ray observations and by timing analysis of the very long data span provided by gamma-ray space detectors. The discovery of peculiar timing and spectral properties, possibly transitional, of the MRPs can be of the utmost importance to link different classes of neutron stars and study their evolution.

  17. Gravitational wave emission from oscillating millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Alford, Mark G.; Schwenzer, Kai

    2015-02-01

    Neutron stars undergoing r-mode oscillation emit gravitational radiation that might be detected on the Earth. For known millisecond pulsars the observed spin-down rate imposes an upper limit on the possible gravitational wave signal of these sources. Taking into account the physics of r-mode evolution, we show that only sources spinning at frequencies above a few hundred Hertz can be unstable to r-modes, and we derive a more stringent universal r-mode spin-down limit on their gravitational wave signal. We find that this refined bound limits the gravitational wave strain from millisecond pulsars to values below the detection sensitivity of next generation detectors. Young sources are therefore a more promising option for the detection of gravitational waves emitted by r-modes and to probe the interior composition of compact stars in the near future.

  18. PuMa, a digital Pulsar Machine

    NASA Astrophysics Data System (ADS)

    Voûte, J. L. L.; Kouwenhoven, M. L. A.; van Haren, P. C.; Langerak, J. J.; Stappers, B. W.; Driesens, D.; Ramachandran, R.; Beijaard, Th. D.

    2002-04-01

    We have designed and constructed PuMa, a pulsar machine that has both a baseband recording and a digital filterbank mode. Its design is based on the use of digital signal processors (DSPs). Their operation is controlled by software, which makes PuMa reconfigurable, flexible and easy to operate. The maximum number of channels in the digital filterbank mode is 32 768 over a bandwidth of 80 MHz. This makes PuMa suitable for pulsar observations at low sky frequencies. The maximum bandwidth in baseband recording mode is two times 10 MHz. The machine was installed at the Westerbork Synthesis Radio Telescope in The Netherlands in 1998. We discuss in some detail PuMa's technical properties and capabilities. Recent observations, a sample of which are presented here, demonstrate its capabilities and that it is performing up to its specifications.

  19. Sustained magnetic fields in binary millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Chanmugam, G.; Brecher, K.

    1987-10-01

    It is proposed here that the magnetic fields of neutron stars do not decay either in binary millisecond pulsars (BMPs) or in general. This eliminates the severe discrepancy between the hypothesis that neutron stars in BMPs formed from the accretion-induced collapse of white dwarfs with shorter orbital periods and the observation that the fraction of pulsars which are BMPs is too large by a factor of over 100. It is also shown that, if such neutron stars are formed from the accretion-induced magnetic flux and an angular momentum-conserving collapse of white dwarfs, most of them are likely to have been born, and remain, spinning rapidly and to have weak magnetic fields, in agreement with observations of BMPs and low-mass X-ray binaries.

  20. Tackling radio polarization of energetic pulsars

    SciTech Connect

    Craig, H. A.

    2014-08-01

    The traditional, geometrical rotating vector model (RVM) has proved particularly poor at capturing the polarization sweeps of the young energetic and millisecond pulsars detected by Fermi. We augment this model by including finite altitude effects using a swept back vacuum dipole geometry. By further including the effects of orthogonal mode jumps, multiple emission altitudes, open zone growth via y-point lowering, and interstellar scattering, we show that a wide range of departures from RVM can be modeled well while retaining a geometrical picture. We illustrate these effects by fitting six Fermi-detected pulsars (J0023+0923, J1024–0719, J1744–1134, J1057–5226, J1420–6048, and J2124–3358) and we describe how such modeling can improve our understanding of their emission geometry.

  1. PARTICLE TRANSPORT IN YOUNG PULSAR WIND NEBULAE

    SciTech Connect

    Tang Xiaping; Chevalier, Roger A. E-mail: rac5x@virginia.edu

    2012-06-20

    The model for pulsar wind nebulae (PWNe) as a result of the magnetohydrodynamic (MHD) downstream flow from a shocked, relativistic pulsar wind has been successful in reproducing many features of the nebulae observed close to central pulsars. However, observations of well-studied young nebulae like the Crab Nebula, 3C 58, and G21.5-0.9 do not show the toroidal magnetic field on a larger scale that might be expected in the MHD flow model; in addition, the radial variation of spectral index due to synchrotron losses is smoother than expected in the MHD flow model. We find that pure diffusion models can reproduce the basic data on nebular size and spectral index variation for the Crab, 3C 58, and G21.5-0.9. Most of our models use an energy-independent diffusion coefficient; power-law variations of the coefficient with energy are degenerate with variation in the input particle energy distribution index in the steady state, transmitting boundary case. Energy-dependent diffusion is a possible reason for the smaller diffusion coefficient inferred for the Crab. Monte Carlo simulations of the particle transport allowing for advection and diffusion of particles suggest that diffusion dominates over much of the total nebular volume of the Crab. Advection dominates close to the pulsar and is likely to play a role in the X-ray half-light radius. The source of diffusion and mixing of particles is uncertain, but may be related to the Rayleigh-Taylor instability at the outer boundary of a young PWN or to instabilities in the toroidal magnetic field structure.

  2. Tests of general relativity using pulsars

    NASA Technical Reports Server (NTRS)

    Reichley, P. E.

    1971-01-01

    The arrival times of the pulses from each pulsar are measured by a cesium clock. The observations are all made at a frequency of 2388 MHz (12.5 cm wavelength) on a 26 m dish antenna. The effect of interstellar charged particles is a random one that increases the noise level on the arrival time measurements. The variation in clock rate is shown consisting of two effects: the time dilation effect of special relativity and the red shift effect of general relativity.

  3. Geminga’s Puzzling Pulsar Wind Nebula

    NASA Astrophysics Data System (ADS)

    Posselt, B.; Pavlov, G. G.; Slane, P. O.; Romani, R.; Bucciantini, N.; Bykov, A. M.; Kargaltsev, O.; Weisskopf, M. C.; Ng, C.-Y.

    2017-01-01

    We report on six new Chandra observations of the Geminga pulsar wind nebula (PWN). The PWN consists of three distinct elongated structures—two ≈ 0.2{d}250 pc long lateral tails and a segmented axial tail of ≈ 0.05{d}250 pc length, where {d}250=d/(250 {pc}). The photon indices of the power-law spectra of the lateral tails, {{Γ }}≈ 1, are significantly harder than those of the pulsar ({{Γ }}≈ 1.5) and the axial tail ({{Γ }}≈ 1.6). There is no significant diffuse X-ray emission between the lateral tails—the ratio of the X-ray surface brightness between the south tail and this sky area is at least 12. The lateral tails apparently connect directly to the pulsar and show indications of moving footpoints. The axial tail comprises time-variable emission blobs. However, there is no evidence for constant or decelerated outward motion of these blobs. Different physical models are consistent with the observed morphology and spectra of the Geminga PWN. In one scenario, the lateral tails could represent an azimuthally asymmetric shell whose hard emission is caused by the Fermi acceleration mechanism of colliding winds. In another scenario, the lateral tails could be luminous, bent polar outflows, while the blobs in the axial tail could represent a crushed torus. In a resemblance to planetary magnetotails, the blobs of the axial tail might also represent short-lived plasmoids, which are formed by magnetic field reconnection in the relativistic plasma of the pulsar wind tail.

  4. FERMI-LAT SEARCH FOR PULSAR WIND NEBULAE AROUND GAMMA-RAY PULSARS

    SciTech Connect

    Ackermann, M.; Ajello, M.; Bechtol, K.; Berenji, B.; Bloom, E. D.; Borgland, A. W.; Bouvier, A.; Buehler, R.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Brez, A.; Ballet, J.; Bastieri, D.; Buson, S.; Bonamente, E.; Brigida, M.; Bruel, P.

    2011-01-01

    The high sensitivity of the Fermi-LAT (Large Area Telescope) offers the first opportunity to study faint and extended GeV sources such as pulsar wind nebulae (PWNe). After one year of observation the LAT detected and identified three PWNe: the Crab Nebula, Vela-X, and the PWN inside MSH 15-52. In the meantime, the list of LAT detected pulsars increased steadily. These pulsars are characterized by high energy loss rates ( E-dot ) from {approx}3 x 10{sup 33} erg s{sup -1} to 5 x 10{sup 38} erg s{sup -1} and are therefore likely to power a PWN. This paper summarizes the search for PWNe in the off-pulse windows of 54 LAT-detected pulsars using 16 months of survey observations. Ten sources show significant emission, seven of these likely being of magnetospheric origin. The detection of significant emission in the off-pulse interval offers new constraints on the {gamma}-ray emitting regions in pulsar magnetospheres. The three other sources with significant emission are the Crab Nebula, Vela-X, and a new PWN candidate associated with the LAT pulsar PSR J1023-5746, coincident with the TeV source HESS J1023-575. We further explore the association between the HESS and the Fermi source by modeling its spectral energy distribution. Flux upper limits derived for the 44 remaining sources are used to provide new constraints on famous PWNe that have been detected at keV and/or TeV energies.

  5. Braking index of isolated pulsars. II. A novel two-dipole model of pulsar magnetism

    NASA Astrophysics Data System (ADS)

    Hamil, O.; Stone, N. J.; Stone, J. R.

    2016-09-01

    The magnetic dipole radiation model is currently the best approach we have to explain pulsar radiation. However, a most characteristic parameter of the observed radiation, the braking index nobs , shows deviations for all the eight best studied isolated pulsars, from the simple model prediction ndip=3 . The index depends upon the rotational frequency and its first and second time derivatives but also on the assumption that the magnetic dipole moment and inclination angle and the moment of inertia of the pulsar are constant in time. In a recent paper [Phys. Rev. D 91, 063007 (2015)], we showed conclusively that changes in the moment of inertia with frequency alone cannot explain the observed braking indices. Possible observational evidence for the magnetic dipole moment migrating away from the rotational axis at a rate α ˙ ˜0.6 ° per 100 years over the lifetime of the Crab pulsar has been recently suggested by Lyne et al. In this paper, we explore the magnetic dipole radiation model with constant moment of inertia and magnetic dipole moment but variable inclination angle α . We first discuss the effect of the variation of α on the observed braking indices and show they all can be understood. However, no explanation for the origin of the change in α is provided. After discussion of the possible source(s) of magnetism in pulsars, we propose a simple mechanism for the change in α based on a toy model in which the magnetic structure in pulsars consists of two interacting dipoles. We show that such a system can explain the Crab observation and the measured braking indices.

  6. Particle acceleration in axisymmetric pulsar current sheets

    NASA Astrophysics Data System (ADS)

    Cerutti, Benoît; Philippov, Alexander; Parfrey, Kyle; Spitkovsky, Anatoly

    2015-03-01

    The equatorial current sheet in pulsar magnetospheres is often regarded as an ideal site for particle acceleration via relativistic reconnection. Using 2D spherical particle-in-cell simulations, we investigate particle acceleration in the axisymmetric pulsar magnetosphere as a function of the injected plasma multiplicity and magnetization. We observe a clear transition from a highly charge-separated magnetosphere for low plasma injection with little current and spin-down power, to a nearly force-free solution for high plasma multiplicity characterized by a prominent equatorial current sheet and high spin-down power. We find significant magnetic dissipation in the current sheet, up to 30 per cent within 5 light-cylinder radii in the high-multiplicity regime. The simulations unambiguously demonstrate that the dissipated Poynting flux is efficiently channelled to the particles in the sheet, close to the Y-point within about 1-2 light-cylinder radii from the star. The mean particle energy in the sheet is given by the upstream plasma magnetization at the light cylinder. The study of particle orbits shows that all energetic particles originate from the boundary layer between the open and the closed field lines. Energetic positrons always stream outwards, while high-energy electrons precipitate back towards the star through the sheet and along the separatrices, which may result in auroral-like emission. Our results suggest that the current sheet and the separatrices may be the main source of high-energy radiation in young pulsars.

  7. Pulsar Magnetospheres: Beyond the Flat Spacetime Dipole

    NASA Astrophysics Data System (ADS)

    Gralla, Samuel E.; Lupsasca, Alexandru; Philippov, Alexander

    2016-12-01

    Most studies of the pulsar magnetosphere have assumed a pure magnetic dipole in flat spacetime. However, recent work suggests that the effects of general relativity are in fact of vital importance and that realistic pulsar magnetic fields will have a significant nondipolar component. We introduce a general analytical method for studying the axisymmetric force-free magnetosphere of a slowly rotating star of arbitrary magnetic field, mass, radius, and moment of inertia, including all the effects of general relativity. We confirm that spacelike current is generically present in the polar caps (suggesting a pair production region), irrespective of the stellar magnetic field. We show that general relativity introduces a ∼ 60 % correction to the formula for the dipolar component of the surface magnetic field inferred from spindown. Finally, we show that the location and shape of the polar caps can be modified dramatically by even modestly strong higher moments. This can affect emission processes occurring near the star and may help explain the modified beam characteristics of millisecond pulsars.

  8. Multiwavelength analysis of four millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Guillemot, L.; Cognard, I.; Johnson, T. J.; Venter, C.; Harding, A. K.

    2011-08-01

    Radio timing observations of millisecond pulsars (MSPs) in support of Fermi LAT observations of the gamma-ray sky enhance the sensitivity of high-energy pulsation searches. With contemporaneous ephemerides we have detected gamma-ray pulsations from PSR B1937+21, the first MSP ever discovered, and B1957+20, the first known black-widow system. The two MSPs share a number of properties: they are energetic and distant compared to other gamma-ray MSPs, and both of them exhibit aligned radio and gamma-ray emission peaks, indicating co-located emission regions in the outer magnetosphere of the pulsars. However, radio observations are also crucial for revealing MSPs in Fermi unassociated sources. In a search for radio pulsations at the position of such unassociated sources, the Nançay Radio Telescope discovered two MSPs, PSRs J2017+0603 and J2302+4442, increasing the sample of known Galactic disk MSPs. Subsequent radio timing observations led to the detection of gamma-ray pulsations from these two MSPs as well. We describe multiwavelength timing and spectral analysis of these four pulsars, and the modeling of their gamma-ray light curves in the context of theoretical models.

  9. Partial accretion regime of accreting millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Eksi, Kazim

    2016-07-01

    The inner parts of the disks around neutron stars in low mass X-ray binaries may become geometrically thick due to inhibition of accretion at the disk mid-plane when the central object is rotating rapidly. In such a case matter inflowing through the disk may keep accreting onto the poles of the neutron star from the parts of the disk away from the disk mid-plane while the matter is propelled at the disk mid-plane. An important ingredient of the evolution of millisecond pulsars is then the fraction of the inflowing matter that can accrete onto the poles in the fast rotation regime depending on the fastness parameter. This ``soft'' propeller regime may be associated with the rapid decay stage observed in the light curves of several accreting millisecond pulsars. To date only a few studies considered the partial accretion regime. By using geometrical arguments we improve the existing studies and test the model by reproducing the lightcurves of millisecond X-ray pulsars via time dependent simulations of disk evolution. We also present analytical solutions that represent disks with partial accretion.

  10. Genesis stories for the millisecond pulsar

    NASA Astrophysics Data System (ADS)

    Ruderman, M. A.; Shaham, J.

    1983-09-01

    Theoretical models proposed to explain the origin of the millisecond pulsar (MP) PSR 1937+214 are reviewed, examining their ability to explain its low surface dipole magnetic field (B), its low birth temperature (less than 10 to the 8th K), the absence of a companion or remnant, and its low velocity perpendicular to the Galactic plane. The models discussed are a single isolated explosion forming a rapidly spinning neutron star, spin-up of a dead pulsar by accretion from a companion, collapse of an accreting spinning white dwarf, and fusion of a tight binary composed of two old neutron stars. Although all of the models have difficulties in explaining one or more of the MP characteristics, the second model is found to be most probable in the light of present knowledge. The lack of a companion is explained by its tidal disruption after it had fed the accreting pre-pulsar for 1 Gyr or more and its mass had decreased to about 0.01 solar mass. Neutron stars accreting in this way have been observed in Galactic-bulge X-ray sources.

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

    SciTech Connect

    Lobato, Ronaldo V.; Malheiro, M.; Coelho, J. G.

    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.

  12. AB INITIO PULSAR MAGNETOSPHERE: THREE-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS OF AXISYMMETRIC PULSARS

    SciTech Connect

    Philippov, Alexander A.; Spitkovsky, Anatoly

    2014-04-20

    We perform ''first-principles'' relativistic particle-in-cell simulations of aligned pulsar magnetosphere. We allow free escape of particles from the surface of a neutron star and continuously populate the magnetosphere with neutral pair plasma to imitate pair production. As pair plasma supply increases, we observe the transition from a charge-separated ''electrosphere'' solution with trapped plasma and no spin-down to a solution close to the ideal force-free magnetosphere with electromagnetically dominated pulsar wind. We calculate the magnetospheric structure, current distribution, and spin-down power of the neutron star. We also discuss particle acceleration in the equatorial current sheet.

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

    NASA Astrophysics Data System (ADS)

    Lobato, Ronaldo V.; Coelho, J. G.; Malheiro, M.

    2015-12-01

    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 ˜ 107 - 1010 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.

  14. XTE J2123-058: A New Neutron Star X-Ray Transient

    NASA Astrophysics Data System (ADS)

    Tomsick, John A.; Halpern, Jules P.; Kemp, Jonathan; Kaaret, Philip

    1999-08-01

    We report on optical and RXTE observations of a new high-latitude bursting X-ray transient, XTE J2123-058. We identified the optical counterpart and discovered a 5.9573+/-0.0016 hr periodic optical modulation, which was subsequently shown to be the same as the spectroscopic orbital period. From the absence of orbital X-ray modulation and the presence of partial optical eclipses we conclude that the binary inclination is between 55° and 73°. From the optical magnitude in quiescence and from the X-ray flux of type I X-ray bursts, we estimate that the source distance is between 4.5 and 15 kpc, which implies that the source is unusually far from the Galactic plane, since b=-36.2d. Optical bursts with properties consistent with being reprocessed X-ray bursts occurred. We detected a pair of high-frequency quasi-periodic oscillations (QPOs) at 847.1+/-5.5 Hz and 1102+/-13 Hz simultaneously. According to the beat-frequency model, this QPO separation implies a neutron star spin period of 3.92+/-0.22 ms. A change in the energy spectrum occurred during the decay of the outburst, which may have been due to the onset of the propeller mechanism. If so, then the neutron star magnetic field strength is between 2 and 8×108 G for an assumed distance of 10 kpc. However, the changes in the timing and spectral properties observed during the decay are typical of atoll sources, which may indicate that the changes are due solely to the dynamics of the accretion disk. As the phase-averaged V-band magnitude declined from 17.26 at the peak of the outburst to 19.24, and the X-ray flux decreased from 9.6×10-10 to 7.3×10-11 ergs cm-2 s-1, the peak-to-peak amplitude of the V-band modulation increased from 0.75 to 1.49 mag. This behavior can be explained if the size of the accretion disk decreases during the decay of the outburst.

  15. High-School Teams Joining Massive Pulsar Search

    NASA Astrophysics Data System (ADS)

    2008-09-01

    High school students and teachers will join astronomers on the cutting edge of science under a program to be operated by the National Radio Astronomy Observatory (NRAO) and West Virginia University (WVU), and funded by the National Science Foundation (NSF). The program, called the Pulsar Search Collaboratory, will engage West Virginia students and teachers in a massive search for new pulsars using data from the Robert C. Byrd Green Bank Telescope (GBT). Sue Ann Heatherly Sue Ann Heatherly, NRAO Education Officer CREDIT: Bill Saxton, NRAO/AUI/NSF (Click on image for larger version) The NSF announced a $892,838 grant to NRAO and WVU to conduct the three-year program. The project will involve 60 teachers and some 600 students in helping astronomers analyze data from 1500 hours of observing time on the GBT. The 120 terabytes of data produced by some 70,000 individual pointings of the giant, 17-million-pound telescope is expected to reveal dozens of previously-unknown pulsars. "The students in this program will be partners in frontier research, discovering new pulsars and measuring changes in pulsars already known," said Sue Ann Heatherly, the NRAO Education Officer in Green Bank and Principal Investigator in the project. Pulsars are superdense neutron stars, the corpses of massive stars that have exploded as supernovae. As the neutron star spins, lighthouse-like beams of radio waves, streaming from the poles of its powerful magnetic field, sweep through space. When one of these beams sweeps across the Earth, radio telescopes can capture the pulse of radio waves. Pulsars serve as exotic laboratories for studying the physics of extreme conditions. Scientists can learn valuable new information about the physics of subatomic particles, electromagnetics, and General Relativity by observing pulsars and the changes they undergo over time. The Pulsar Search Collaboratory (PSC) combines the capabilities of NRAO and WVU to provide a unique opportunity for teachers and students

  16. Detecting dark matter with imploding pulsars in the galactic center.

    PubMed

    Bramante, Joseph; Linden, Tim

    2014-11-07

    The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent.

  17. X-ray studies of three binary millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Webb, N. A.; Olive, J.-F.; Barret, D.

    2005-10-01

    It is thought that millisecond pulsars with white dwarf companions are born from X-ray binaries. The majority of known systems have been studied uniquely in the radio domain, which limits our understanding of such systems. We present here the X-ray observations of the millisecond pulsar PSR J0218+4232 and the two faint millisecond pulsars PSR J0751+1807 and PSR J1012+5307, which we discuss in conjunction with radio observations. We confirm the previously detected X-ray pulsations of PSR J0218+4232 and we show that its folded lightcurve is strongly dependent on energy. We present evidence to suggest that the broad band X-ray spectrum for this pulsar may not be a simple power law, but that there is some evidence for an excess of soft thermal emission over the power law spectrum, in particular from the strongest pulse, in support of a heated polar cap model for this pulsar. We also present the X-ray spectra of the two faint millisecond pulsars as well as some evidence to suggest that both of these millisecond pulsars show pulsations in the X-ray band. We then discuss the implied nature of the magnetic field configuration as a means of discriminating between competing magnetic field evolution theories in millisecond pulsars.

  18. Prospects for Pulsar Studies with the GLAST Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2007-01-01

    The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST), due to launch in November 2007, will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered pulsars. As the only presently known galactic GeV source class; pulsars will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma-ray pulsars, including millisecond pulsars, giving much better statistics for elucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric particle acceleration and radiation mechanisms, by comparing data with theoretical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all unidentified EGRET sources, to possibly uncover more radio-quiet Geminga-like pulsars.

  19. Prospects for Pulsar Studies with the GLAST Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2006-01-01

    The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST) will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered pulsars. As the only presently known galactic GeV source class, pulsars will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma ray pulsars, including millisecond pulsars, giving much better statistics for elucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric particle acceleration and radiation mechanisms, by comparing data with theoretical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all unidentified EGRET sources, to possibly uncover more radio-quiet Geminga-like pulsars.

  20. Electromagnetic tornado in the vacuum gap of a pulsar

    SciTech Connect

    Kontorovich, V. M.

    2010-06-15

    The solution for an electromagnetic tornado that describes the motion in the discharge filament of breakdown in the vacuum gap of a pulsar has been obtained. This solution can serve as an explanation of the observed circular polarization of giant radiation pulses from pulsars.

  1. THE PECULIAR PULSAR POPULATION OF THE CENTRAL PARSEC

    SciTech Connect

    Dexter, Jason; O'Leary, Ryan M. E-mail: oleary@berkeley.edu

    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.

  2. Construction and Identification of Profiles of Curvature Radiation of Pulsars

    NASA Astrophysics Data System (ADS)

    Avdyushev, V. A.; Bordovitsyn, V. A.; Grokhovskaya, A. A.

    2017-03-01

    Parameters of the observed radiation of pulsars are identified with the help of numerical simulation within the framework of the nonlinear least squares problem. With the help of the obtained parameter values, we have constructed profiles of radiation and indicatrices of the angular distribution of the instantaneous radiated power for experimentally observed pulsars.

  3. Parameters of radio pulsars in binary systems and globular clusters

    NASA Astrophysics Data System (ADS)

    Loginov, A. A.; Malov, I. F.

    2017-02-01

    The parameters of radio pulsars in binary systems and globular clusters are investigated. It is shown that such pulsars tend to have short periods (of the order of several milliseconds). Themagnetic fields of most of the pulsars considered are weak (surface fields of the order of 108-109 G). This corresponds to the generally accepted view that short-period neutron stars are spun up by angular momentum associated with the stellar wind from a companion. However, the fields at the light cylinders in these objects are two to three orders of magnitude higher than for the main population of single neutron stars. The dependence of the pulse width on the period does not differ from the corresponding dependences for single pulsars, assuming the emission is generated inside the polar cap, at moderate distances from the surface or near the light cylinder. The radio luminosities of pulsars in binary systems do not show the correlation with the rate of loss of rotational energy that is characteristic for single pulsars, probably due to the influence of accreting matter from a companion. Moreover, accretion apparently decreases the power of the emergent radiation, and can explain the observed systematic excess of the radio luminosity of single pulsars compared to pulsars in binary systems. The distributions and dependences presented in the article support generally accepted concepts concerning the processes occurring in binary systems containing neutron stars.

  4. Rapidly rotating pulsar radiation in vacuum nonlinear electrodynamics

    NASA Astrophysics Data System (ADS)

    Denisov, V. I.; Denisova, I. P.; Pimenov, A. B.; Sokolov, V. A.

    2016-11-01

    In this paper we investigate the corrections of vacuum nonlinear electrodynamics on rapidly rotating pulsar radiation and spin-down in the perturbative QED approach (post-Maxwellian approximation). An analytical expression for the pulsar's radiation intensity has been obtained and analyzed.

  5. The Use of X-Ray Pulsars for Aiding GPS Satellite Orbit Determination

    DTIC Science & Technology

    2005-03-01

    pulsar used was PSR B0531+21 (Crab Pulsar) which is a very well known bright pulsar in the Crab Nebula [28]. Feasibly, if GPS x-ray detectors were 4...Variations Within the Pulse Profile Peaks of the Crab Nebula Pulsar,” The Astrophysical Journal , 467 (1996). 18. Halsell, Charles A. Orbit

  6. Pulsars, X-ray synchrotron nebulae, and guest stars

    NASA Technical Reports Server (NTRS)

    Seward, Frederick D.; Wang, Zhen-Ru

    1988-01-01

    X-ray observations of supernova remnants and radio pulsars are used to derive luminosities of neutron stars and synchrotron nebulae. Observations of known isolated pulsars are used to develop an empirical relationship between the X-ray luminosity and the rate of loss of rotational energy. This is used to derive the characteristics of pulsars hidden in remnants which show evidence for a central compact object or associated nebular emission, but no clear pulsed signal from the neutron star itself. Possible periods and period derivatives for the hidden pulsars are discussed. Some might have periods as long as 0.5 s, and period derivatives considerably higher than that of PSR 1509 - 58, currently the pulsar with the highest known period derivative.

  7. Do the enigmatic ``Infrared-Faint Radio Sources'' include pulsars?

    NASA Astrophysics Data System (ADS)

    Hobbs, George; Middelberg, Enno; Norris, Ray; Keith, Michael; Mao, Minnie; Champion, David

    2009-04-01

    The Australia Telescope Large Area Survey (ATLAS) team have surveyed seven square degrees of sky at 1.4GHz. During processing some unexpected infrared-faint radio sources (IFRS sources) were discovered. The nature of these sources is not understood, but it is possible that some of these sources may be pulsars within our own galaxy. We propose to observe the IFRS sources with steep spectral indices using standard search techniques to determine whether or not they are pulsars. A pulsar detection would 1) remove a subset of the IFRS sources from the ATLAS sample so they would not need to be observed with large optical/IR telescopes to find their hosts and 2) be intrinsically interesting as the pulsar would be a millisecond pulsar and/or have an extreme spatial velocity.

  8. On the search for coherent radiation from radio pulsars

    NASA Astrophysics Data System (ADS)

    Smits, J. M.; Stappers, B. W.; Macquart, J.-P.; Ramachandran, R.; Kuijpers, J.

    2003-07-01

    We have examined data from pulsars B0950+08 and B0329+54 for evidence of temporally coherent radiation using the modified coherence function (MCF) technique of \\citet{Jenet}. We consider the influence of both instrumental bandpass and interstellar propagation effects. Even after removal of the effects due to the instrumental bandpass, we detect a signature in the MCF of our PSR B0329+54 data which is consistent with the definition of a coherent signal. However, we model the effects due to interstellar scintillation for this pulsar and show that it reproduces the observed signature. In particular, the temporal coherence time is close to the reciprocal of the decorrelation bandwidth due to diffractive scintillation. Furthermore, comparison of the coherence times of three pulsars reported by \\citet{Jenet} with their expected diffractive decorrelation bandwidths suggests that the detection of coherence in these pulsars is also likely a result of interstellar scintillation, and is not intrinsic to the pulsars.

  9. Pulsar Search Results from the Arecibo Remote Command Center

    NASA Astrophysics Data System (ADS)

    Rodriguez, Miguel; Stovall, Kevin; Banaszak, Shawn A.; Becker, Alison; Biwer, Christopher M.; Boehler, Keith; Caballero, Keeisi; Christy, Brian; Cohen, Stephanie; Crawford, Fronefield; Cuellar, Andres; Danford, Andrew; Percy Dartez, Louis; Day, David; Flanigan, Joseph D.; Fonrouge, Aldo; Gonzalez, Adolfo; Gustavson, Kathy; Handzo, Emma; Hinojosa, Jesus; Jenet, Fredrick A.; Kaplan, David L. A.; Lommen, Andrea N.; Longoria, Chasity; Lopez, Janine; Lunsford, Grady; Mahany, Nicolas; Martinez, Jose; Mata, Alberto; Miller, Andy; Murray, James; Pankow, Chris; Ramirez, Ivan; Reser, Jackie; Rojas, Pablo; Rohr, Matthew; Rolph, Kristina; Rose, Caitlin; Rudnik, Philip; Siemens, Xavier; Tellez, Andrea; Tillman, Nicholas; Walker, Arielle; Wells, Bradley L.; Zaldivar, Jonathan; Zermeno, Adrienne; Gbncc Consortium, Palfa Consortium, Gbtdrift Consortium, Ao327 Consortium

    2015-01-01

    This poster presents the pulsar discoveries made by students in the Arecibo Remote Command Center (ARCC) program. The ARCC program was started at the University of Texas - Brownsville (UTB) within the Center for Advanced Radio Astronomy (CARA) as a group of scientists, faculty, graduate, undergraduate, and high school students interested in astrophysics. It has since expanded to form other ARCC programs at the University of Wisconsin-Milwaukee (UWM) and Franklin and Marshall College (F&M). The students in the ARCC group control the world's largest radio telescopes to search and discover pulsars. Pulsars are exotic neutron stars that emit beams of electromagnetic radiation. ARCC students use a web application to view and rate the images of radio pulsar candidates based on their signal characteristics. To date, ARCC students have searched through thousands of candidates and have discovered 61 pulsars to date.

  10. PROPAGATION AND STABILITY OF SUPERLUMINAL WAVES IN PULSAR WINDS

    SciTech Connect

    Mochol, Iwona; Kirk, John G. E-mail: john.kirk@mpi-hd.mpg.de

    2013-07-01

    Nonlinear electromagnetic waves with superluminal phase velocity can propagate in the winds around isolated pulsars, and around some pulsars in binary systems. Using a short-wavelength approximation, we find and analyze an integrable system of equations that govern their evolution in spherical geometry. A confined mode is identified that stagnates to finite pressure at large radius and can form a precursor to the termination shock. Using a simplified criterion, we find this mode is stable for most isolated pulsars, but may be unstable if the external pressure is high, such as in the pulsar wind nebulae in starburst galaxies and in W44. Pulsar winds in eccentric binary systems, such as PSR 1259-63, may go through phases with stable and unstable electromagnetic precursors, as well as phases in which the density is too high for these modes to propagate.

  11. Binary millisecond pulsar discovery via gamma-ray pulsations.

    PubMed

    Pletsch, H J; Guillemot, L; Fehrmann, H; Allen, B; Kramer, M; Aulbert, C; Ackermann, M; Ajello, M; de Angelis, A; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Borgland, A W; Bottacini, E; Brandt, T J; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cecchi, C; Çelik, Ö; Charles, E; Chaves, R C G; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cutini, S; D'Ammando, F; Dermer, C D; Digel, S W; Drell, P S; Drlica-Wagner, A; Dubois, R; Dumora, D; Favuzzi, C; Ferrara, E C; Franckowiak, A; Fukazawa, Y; Fusco, P; Gargano, F; Gehrels, N; Germani, S; Giglietto, N; Giordano, F; Giroletti, M; Godfrey, G; Grenier, I A; Grondin, M-H; Grove, J E; Guiriec, S; Hadasch, D; Hanabata, Y; Harding, A K; den Hartog, P R; Hayashida, M; Hays, E; Hill, A B; Hou, X; Hughes, R E; Jóhannesson, G; Jackson, M S; Jogler, T; Johnson, A S; Johnson, W N; Kataoka, J; Kerr, M; Knödlseder, J; Kuss, M; Lande, J; Larsson, S; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Massaro, F; Mayer, M; Mazziotta, M N; McEnery, J E; Mehault, J; Michelson, P F; Mitthumsiri, W; Mizuno, T; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nakamori, T; Nemmen, R; Nuss, E; Ohno, M; Ohsugi, T; Omodei, N; Orienti, M; Orlando, E; de Palma, F; Paneque, D; Perkins, J S; Piron, F; Pivato, G; Porter, T A; Rainò, S; Rando, R; Ray, P S; Razzano, M; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Romani, R W; Romoli, C; Sanchez, D A; Saz Parkinson, P M; Schulz, A; Sgrò, C; do Couto e Silva, E; Siskind, E J; Smith, D A; Spandre, G; Spinelli, P; Suson, D J; Takahashi, H; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Tinivella, M; Troja, E; Usher, T L; Vandenbroucke, J; Vasileiou, V; Vianello, G; Vitale, V; Waite, A P; Winer, B L; Wood, K S; Wood, M; Yang, Z; Zimmer, S

    2012-12-07

    Millisecond pulsars, old neutron stars spun up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such "recycled" rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311-3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. The pulsar is in a circular orbit with an orbital period of only 93 minutes, the shortest of any spin-powered pulsar binary ever found.

  12. Study of CdTe/MgxCd1-xTe Double Heterostructures and Their Application in High Efficiency Solar Cells and in Luminescence Refrigeration

    NASA Astrophysics Data System (ADS)

    Zhao, Xinhao

    CdTe/MgxCd1-xTe double heterostructures (DHs) have been grown on lattice matched InSb (001) substrates using Molecular Beam Epitaxy. The MgxCd1-xTe layers, which have a wider bandgap and type-I band edge alignment with CdTe, provide sufficient carrier confinement to CdTe, so that the optical properties of CdTe can be studied. The DH samples show very strong Photoluminescence (PL) intensity, long carrier lifetimes (up to 3.6 micros) and low effective interface recombination velocity at the CdTe/MgxCd1-xTe heterointerface ( 1 cm/s), indicating the high material quality. Indium has been attempted as an n-type dopant in CdTe and it is found that the carriers are 100% ionized in the doping range of 1x1016 cm-3 to 1x1018 cm-3. With decent doping levels, long minority carrier lifetime, and almost perfect surface passivation by the MgxCd 1-xTe layer, the CdTe/MgxCd1-xTe DHs are applied to high efficiency CdTe solar cells. Monocrystalline CdTe solar cells with efficiency of 17.0% and a record breaking open circuit voltage of 1.096 V have been demonstrated in our group. Mg0.13Cd0.87Te (1.7 eV), also with high material quality, has been proposed as a current matching cell to Si (1.1 eV) solar cells, which could potentially enable a tandem solar cell with high efficiency and thus lower the electricity cost. The properties of Mg0.13Cd 0.87Te/Mg0.5Cd0.5Te DHs and solar cells have been investigated. Carrier lifetime as long as 0.56 ?s is observed and a solar cell with 11.2% efficiency and open circuit voltage of 1.176 V is demonstrated. The CdTe/MgxCd1-xTe DHs could also be potentially applied to luminescence refrigeration, which could be used in vibration-free space applications. Both external luminescence quantum efficiency and excitation-dependent PL measurement show that the best quality samples are almost 100% dominated by radiative recombination, and calculation shows that the internal quantum efficiency can be as high as 99.7% at the optimal injection level (10 17 cm-3

  13. FREQUENCY DEPENDENCE OF PULSE WIDTH FOR 150 RADIO NORMAL PULSARS

    SciTech Connect

    Chen, J. L.; Wang, H. G.

    2014-11-01

    The frequency dependence of the pulse width is studied for 150 normal pulsars, mostly selected from the European Pulsar Network, for which the 10% multifrequency pulse widths can be well fit with the Thorsett relationship W {sub 10} = Aν{sup μ} + W {sub 10,} {sub min}. The relative fraction of pulse width change between 0.4 GHz and 4.85 GHz, η = (W {sub 4.85} – W {sub 0.4})/W {sub 0.4}, is calculated in terms of the best-fit relationship for each pulsar. It is found that 81 pulsars (54%) have η < –10% (group A), showing considerable profile narrowing at high frequencies, 40 pulsars (27%) have –10% ≤η ≤ 10% (group B), meaning a marginal change in pulse width, and 29 pulsars (19%) have η > 10% (group C), showing a remarkable profile broadening at high frequencies. The fractions of the group-A and group-C pulsars suggest that the profile narrowing phenomenon at high frequencies is more common than the profile broadening phenomenon, but a large fraction of the group-B and group-C pulsars (a total of 46%) is also revealed. The group-C pulsars, together with a portion of group-B pulsars with slight pulse broadening, can hardly be explained using the conventional radius-to-frequency mapping, which only applies to the profile narrowing phenomenon. Based on a recent version of the fan beam model, a type of broadband emission model, we propose that the diverse frequency dependence of pulse width is a consequence of different types of distribution of emission spectra across the emission region. The geometrical effect predicting a link between the emission beam shrinkage and spectrum steepening is tested but disfavored.

  14. Spin-down of Pulsars, and Their Electromagnetic and Gravitational Wave Radiations

    NASA Astrophysics Data System (ADS)

    Yue-zhu, Zhang; Yan-yan, Fu; Yi-huan, Wei; Cheng-min, Zhang; Shao-hua, Yu; Yuan-yue, Pan; Yuan-qi, Guo; De-hua, Wang

    2016-04-01

    Pulsars posses extremely strong magnetic fields, and their magnetic axis does not coincide with their rotation axis, this causes the pulsars to emit electromagnetic radiations. Pulsars rely on their rotational energy to compensate for the energy loss caused by the electromagnetic radiation, which leads to the gradually decelerated spin of pulsars. According to the theoretical deduction, we have calculated the initial period of the Crab Nebula pulsar, and derived the period evolution of the pulsar at any time in the future under the effect of the electromagnetic radiation. Considered the possible existence of quadrupole moment in the mass distribution of a pulsar, the gravitational wave radiation will also make the pulsar spin down, hence the variation of spin period of the Crab pulsar under the effect of gravitational wave radiation is further analyzed. Finally, combining the two kinds of radiation mechanisms, the evolution of spin period of the Crab pulsar under the joint action of these two kinds of radiation mechanisms is analyzed.

  15. The thermal diffusivity of Mn_xCd_1-xTe using the interferometric Mirage effect

    NASA Astrophysics Data System (ADS)

    Corona-Organiche, Edgar; Munoz-Aguirre, Narcizo; Morales-Toro, Juan Eduardo; Vazquez-Lopez, Carlos; Zelaya-Angel, Orlando; Lopez-Cruz, Elias

    2001-03-01

    Recently, N. Munoz-Aguirre et. al (N. Munoz-Aguirre, G. Gonzalez de la Cruz, Yu. G. Gurevich, G.N. Logvinov, and M.N. Kasyanchuk, Phys. Stat. Sol. (b), vol. 220, p. 781 (2000))reported a theoretical treatment of the heat diffusion in two-layer structures for application to photoacoustic experiments. They showed that the influence of the interface thermal contact between the layers plays an important role on the effective thermal parameters. In this work, the theory has been extended to the case of the Mirage effect detected by means of a Michelson-Morley interferometer, and applied to the system air-Mn_xCd_1-xTe, with x in the range 0.05 - 0.60.

  16. X-ray diffuse scattering study of local distortions in Fe1+xTe induced by excess Fe

    NASA Astrophysics Data System (ADS)

    Liu, X.; Lee, C.-C.; Xu, Z. J.; Wen, J. S.; Gu, G.; Ku, W.; Tranquada, J. M.; Hill, J. P.

    2011-05-01

    We report x-ray diffuse scattering studies of the iron chalcogenide Fe1+xTe as a function of doping and temperature for x=0.03, 0.08, and 0.12. In all cases, remarkably strong, characteristic diffuse scattering is observed. This scattering extends throughout the Brillouin zone and exhibits a nonmonotonic decay away from the fundamental Bragg peaks, with a peaklike structure at a reduced q≈(0.3,0,0.6). We interpret this scattering as Huang diffuse scattering resulting from distortions induced by the interaction between the excess Fe and the FeTe layers. The form of the scattering indicates that this interaction is strong and extends a number of unit cells away from the interstitial Fe site. Further, the diffuse scattering shows a sudden decrease on cooling through the structural and magnetic phase transition, reflecting the first-order change of the electronic structure of FeTe.

  17. USA Observation of Spectral and Timing Evolution During the 2000 Outburst of XTE J1550--564

    SciTech Connect

    Reilly, Kaice T

    2002-12-06

    We report on timing and spectral observations of the 2000 outburst of XTE J1550--564 made by the Unconventional Stellar Aspect (USA) Experiment on board the Advanced Research and Global Observation Satellite (ARGOS). We observe a low-frequency quasi-periodic oscillation (LFQPO) with a centroid frequency that tends to increase with increasing flux and a fractional rms amplitude which is correlated with the hardness ratio. Several high-frequency quasi-periodic oscillations (HFQPO) were detected by RXTE, during periods where the LFQPO is seen to be weakening or not detectable at all. The evolution of the hardness ratio (4-16 keV/1-4 keV) with time and source flux is examined. The hardness-intensity diagram (HID) shows a cyclical movement in the counterclockwise direction and possibly indicates the presence of two independent accretion flows: a thin disk and a hot sub-Keplerian flow.

  18. High-Frequency Quasi-Periodic Oscillations in the Black Hole X-Ray Transient XTE J1650-500

    NASA Technical Reports Server (NTRS)

    Holman, Jeroen; Klein-Wolt, Marc; Rossi, Sabrina; Miller, Jon M.; Wijnands, Rudy; Belloni, Tomaso; VanDerKlis, Michiel; Lewin, Walter H. G.

    2003-01-01

    We report the detection of high-frequency variability in the black hole X-ray transient XTE 51650-500. A quasi-periodic oscillation (QPO) was found at 250 Hz during a transition from the hard to the soft state. We also detected less coherent variability around 50 Hz that disappeared when the 250 Hz QPO showed up. There are indications that when the energy spectrum hardened the QPO frequency increased from approx. 110 to approx. 270 Hz, although the observed frequencies are also consistent with being 1 : 2 : 3 harmonics of each other. Interpreting the 250 Hz as the orbital frequency at the innermost stable orbit around a Schwarzschild black hole leads to a mass estimate of 8.2 solar mass. The spectral results by Miller et al., which suggest considerable black hole spin, would imply a higher mass.

  19. THE FAST SPIRAL-IN OF THE COMPANION STAR TO THE BLACK HOLE XTE J1118+480

    SciTech Connect

    Gonzalez Hernandez, Jonay I.; Rebolo, Rafael; Casares, Jorge E-mail: rrl@iac.es

    2012-01-10

    We report the detection of an orbital period decay of P-dot =-1.83{+-}0.66 ms yr{sup -1} in the black hole X-ray binary XTE J1118+480. This corresponds to a period change of -0.85 {+-} 0.30 {mu}s per orbital cycle, which is {approx}150 times larger than expected from the emission of gravitational waves. These observations cannot be reproduced by conventional models of magnetic braking even when including significant mass loss from the system. The spiral-in of the star is either driven by magnetic braking under extremely high magnetic fields in the secondary star or by a currently unknown process, which will have an impact on the evolution and lifetime of black hole X-ray binaries.

  20. Phase Lag and Coherence Function of X-Ray Emission from Black Hole Candidate XTE J1550-564

    NASA Technical Reports Server (NTRS)

    Cui, Wei; Zhang, Shuang Nan; Chen, Wan

    2000-01-01

    We report the results from measuring the phase lag and coherence function of X-ray emission from black hole candidate XTE J1550-564. These temporal X-ray properties have been recognized to be increasingly important in providing important diagnostics of the dynamics of accretion flows around black holes. For XTE J1550-564, we found significant hard lag-the X-ray variability in high-energy bands lags behind that in low-energy bands-associated both with broadband variability and quasi-periodic oscillation (QPO) . However, the situation is more complicated for the QPO: while hard lag was measured for the first harmonic of the signal, the fundamental component showed significant soft lag. Such behavior is remarkably similar to what was observed of microquasar GRS 1915+105. The phase lag evolved during the initial rising phase of the 1998 outburst. The magnitude of both the soft and hard lags of the QPO increases with X-ray flux, while the Fourier spectrum of the broadband lag varies significantly in shape. The coherence function is relatively high and roughly constant at low frequencies and begins to drop almost right after the first harmonic of the QPO. It is near unity at the beginning and decreases rapidly during the rising phase. Also observed is that the more widely separated the two energy bands are, the less the coherence function between the two. It is interesting that the coherence function increases significantly at the frequencies of the QPO and its harmonics. We discuss the implications of the results on the models proposed for black hole candidates.

  1. XTE J1752-223 in outburst: a persistent radio jet, dramatic flaring, multiple ejections and linear polarization

    NASA Astrophysics Data System (ADS)

    Brocksopp, C.; Corbel, S.; Tzioumis, A.; Broderick, J. W.; Rodriguez, J.; Yang, J.; Fender, R. P.; Paragi, Z.

    2013-06-01

    The black hole candidate, XTE J1752-223, was discovered in 2009 October when it entered an outburst. We obtained radio data from the Australia Telescope Compact Array for the duration of the ˜9 month event. The light curves show that the radio emission from the compact jet persisted for the duration of an extended hard state and through the transition to the intermediate state. The flux then rose rapidly by a factor of 10 and the radio source entered a series of at least seven maxima, the first of which was likely to be emission associated with the compact jet. The subsequent six flares were accompanied by variable behaviour in terms of radio spectrum, degree of linear polarization, morphology and associated X-ray behaviour. They were, however, remarkably similar in terms of the estimated minimum power required to launch such an ejection event. We compare the timing of radio peaks with the location of the ejecta, imaged by contemporaneous Very Long Baseline Interferometry experiments. We then discuss the mechanism behind the events, in terms of whether discrete ejections are the most likely description of the behaviour. One ejection, at least, appears to be travelling with apparent superluminal motion. The range of properties, however, suggests that multiple mechanisms may be relevant and that at least some of the emission is coming from shocked interactions amongst the ejecta and between the ejecta and the interstellar medium. We also compare the radio flux density with the X-ray source during the hard state and conclude that XTE J1752-223 is a radio-weak/X-ray-bright outlier on the universal correlation for black hole transient sources.

  2. MAXI GSC Observations of a Spectral State Transition in the Black Hole Candidate XTE J1752-223

    NASA Astrophysics Data System (ADS)

    Nakahira, Satoshi; Yamaoka, Kazutaka; Sugizaki, Mutsumi; Ueda, Yoshihiro; Negoro, Hitoshi; Ebisawa, Ken; Kawai, Nobuyuki; Matsuoka, Masaru; Tsunemi, Hiroshi; Daikyuji, Arata; Eguchi, Satoshi; Hiroi, Kazuo; Ishikawa, Masaki; Ishiwata, Ryoji; Isobe, Naoki; Kawasaki, Kazuyoshi; Kimura, Masashi; Kohama, Mitsuhiro; Mihara, Tatehiro; Miyoshi, Sho; Morii, Mikio; Nakagawa, Yujin E.; Nakajima, Motoki; Ozawa, Hiroshi; Sootome, Tetsuya; Sugimori, Kousuke; Suzuki, Motoko; Tomida, Hiroshi; Ueno, Shiro; Yamamoto, Takayuki; Yoshida, Atsumasa; Maxi Team

    2010-10-01

    We present the first results on the black-hole candidate XTE J1752-223 from the Gas Slit Camera (GSC) aboard the Monitor of All-sky X-ray Image (MAXI) on the International Space Station. Including the onset of an outburst reported by the Proportional Counter Array aboard the Rossi X-ray Timing Explorer on 2009 October 23, MAXI / GSC has been monitoring this source approximately 10 times per day with high sensitivity in the 2-20 keV band. XTE J1752-223 was initially in a low / hard state during the first 3 months. An anti-correlated behavior between the 2-4 keV and 4-20 keV bands was observed around 2010 January 20, indicating that the source exhibited a spectral transition to the high / soft state. A transient radio jet may have been ejected when the source was in the intermediate state where the spectrum was roughly explained by a power-law with a photon index of 2.5-3.0. The unusually long period in the initial low / hard state implies a slow variation in the mass-accretion rate, and a dramatic soft X-ray increase may be explained by a sudden appearance of the accretion disk component with a relatively low innermost temperature (0.4-0.7 keV). Such a low temperature might suggest that the maximum accretion rate was just above the critical gas-evaporation rate required for the state transition.

  3. CHARACTERIZING INTERMITTENCY OF 4-Hz QUASI-PERIODIC OSCILLATION IN XTE J1550–564 USING HILBERT–HUANG TRANSFORM

    SciTech Connect

    Su, Yi-Hao; Chou, Yi; Hu, Chin-Ping; Yang, Ting-Chang E-mail: yichou@astro.ncu.edu.tw

    2015-12-10

    We present time-frequency analysis results based on the Hilbert–Huang transform (HHT) for the evolution of a 4-Hz low-frequency quasi-periodic oscillation (LFQPO) around the black hole X-ray binary XTE J1550–564. The origin of LFQPOs is still debated. To understand the cause of the peak broadening, we utilized a recently developed time-frequency analysis, HHT, for tracking the evolution of the 4-Hz LFQPO from XTE J1550–564. By adaptively decomposing the ∼4-Hz oscillatory component from the light curve and acquiring its instantaneous frequency, the Hilbert spectrum illustrates that the LFQPO is composed of a series of intermittent oscillations appearing occasionally between 3 and 5 Hz. We further characterized this intermittency by computing the confidence limits of the instantaneous amplitudes of the intermittent oscillations, and constructed both the distributions of the QPO’s high- and low-amplitude durations, which are the time intervals with and without significant ∼4-Hz oscillations, respectively. The mean high-amplitude duration is 1.45 s and 90% of the oscillation segments have lifetimes below 3.1 s. The mean low-amplitude duration is 0.42 s and 90% of these segments are shorter than 0.73 s. In addition, these intermittent oscillations exhibit a correlation between the oscillation’s rms amplitude and mean count rate. This correlation could be analogous to the linear rms-flux relation found in the 4-Hz LFQPO through Fourier analysis. We conclude that the LFQPO peak in the power spectrum is broadened owing to intermittent oscillations with varying frequencies, which could be explained by using the Lense–Thirring precession model.

  4. Characterizing Intermittency of 4-Hz Quasi-periodic Oscillation in XTE J1550-564 Using Hilbert-Huang Transform

    NASA Astrophysics Data System (ADS)

    Su, Yi-Hao; Chou, Yi; Hu, Chin-Ping; Yang, Ting-Chang

    2015-12-01

    We present time-frequency analysis results based on the Hilbert-Huang transform (HHT) for the evolution of a 4-Hz low-frequency quasi-periodic oscillation (LFQPO) around the black hole X-ray binary XTE J1550-564. The origin of LFQPOs is still debated. To understand the cause of the peak broadening, we utilized a recently developed time-frequency analysis, HHT, for tracking the evolution of the 4-Hz LFQPO from XTE J1550-564. By adaptively decomposing the ˜4-Hz oscillatory component from the light curve and acquiring its instantaneous frequency, the Hilbert spectrum illustrates that the LFQPO is composed of a series of intermittent oscillations appearing occasionally between 3 and 5 Hz. We further characterized this intermittency by computing the confidence limits of the instantaneous amplitudes of the intermittent oscillations, and constructed both the distributions of the QPO’s high- and low-amplitude durations, which are the time intervals with and without significant ˜4-Hz oscillations, respectively. The mean high-amplitude duration is 1.45 s and 90% of the oscillation segments have lifetimes below 3.1 s. The mean low-amplitude duration is 0.42 s and 90% of these segments are shorter than 0.73 s. In addition, these intermittent oscillations exhibit a correlation between the oscillation’s rms amplitude and mean count rate. This correlation could be analogous to the linear rms-flux relation found in the 4-Hz LFQPO through Fourier analysis. We conclude that the LFQPO peak in the power spectrum is broadened owing to intermittent oscillations with varying frequencies, which could be explained by using the Lense-Thirring precession model.

  5. Arecibo Pulsar Survey Using ALFA. IV. Mock Spectrometer Data Analysis, Survey Sensitivity, and the Discovery of 40 Pulsars

    NASA Astrophysics Data System (ADS)

    Lazarus, P.; Brazier, A.; Hessels, J. W. T.; Karako-Argaman, C.; Kaspi, V. M.; Lynch, R.; Madsen, E.; Patel, C.; Ransom, S. M.; Scholz, P.; Swiggum, J.; Zhu, W. W.; Allen, B.; Bogdanov, S.; Camilo, F.; Cardoso, F.; Chatterjee, S.; Cordes, J. M.; Crawford, F.; Deneva, J. S.; Ferdman, R.; Freire, P. C. C.; Jenet, F. A.; Knispel, B.; Lee, K. J.; van Leeuwen, J.; Lorimer, D. R.; Lyne, A. G.; McLaughlin, M. A.; Siemens, X.; Spitler, L. G.; Stairs, I. H.; Stovall, K.; Venkataraman, A.

    2015-10-01

    The on-going Arecibo Pulsar-ALFA (PALFA) survey began in 2004 and is searching for radio pulsars in the Galactic plane at 1.4 GHz. Here we present a comprehensive description of one of its main data reduction pipelines that is based on the PRESTO software and includes new interference-excision algorithms and candidate selection heuristics. This pipeline has been used to discover 40 pulsars, bringing the survey’s discovery total to 144 pulsars. Of the new discoveries, eight are millisecond pulsars (MSPs; P\\lt 10 ms) and one is a Fast Radio Burst (FRB). This pipeline has also re-detected 188 previously known pulsars, 60 of them previously discovered by the other PALFA pipelines. We present a novel method for determining the survey sensitivity that accurately takes into account the effects of interference and red noise: we inject synthetic pulsar signals with various parameters into real survey observations and then attempt to recover them with our pipeline. We find that the PALFA survey achieves the sensitivity to MSPs predicted by theoretical models but suffers a degradation for P≳ 100 ms that gradually becomes up to ˜10 times worse for P\\gt 4 {{s}} at {DM}\\lt 150 pc cm-3. We estimate 33 ± 3% of the slower pulsars are missed, largely due to red noise. A population synthesis analysis using the sensitivity limits we measured suggests the PALFA survey should have found 224 ± 16 un-recycled pulsars in the data set analyzed, in agreement with the 241 actually detected. The reduced sensitivity could have implications on estimates of the number of long-period pulsars in the Galaxy.

  6. Cosmic-ray Positrons from Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Venter, C.; Kopp, A.; Harding, A. K.; Gonthier, P. L.; Büsching, I.

    2015-07-01

    Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 GeV. Fermi has also uncovered many new MSPs, impacting Galactic stellar population models. We investigate the contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters.

  7. Strange Stars, Neutron Stars and Pulsar Emission

    NASA Astrophysics Data System (ADS)

    Benvenuto, O. G.; Horvath, J. E.

    1990-11-01

    RESUMEN. Se ha conjeturado que una partlecula de dieciocho quarks, sin Carga, sin espi'n y sin colar (quark-alfa) podri'a ser estable a ba5as tern peraturas y presiones aiTh COfl respecto a materia extrafla. Presentamos en este trabajo la estmctura de estrellas extraflas incluyendo los efectos y apariencia de parti'culas uark-alfa en las capas exteriores. La estruc tura interna ya no es hoinogenea del centro a la superficie, sino que muestra un centro de materia extrafla, capas s6lidas y una costra delgada de materia normal en la superficie. La superficie de materia nonnal permite la fornaci6n de una magnetosfera, la que se piensa sea el sitlo en donde ocurre la emisi6n del pulsar. La superficie de superflui'do ayuda a explicar el fen6rneno de `glitch', el cual ba sido observado en muchos pulsares. Se discute la ecuaci6n de estado para rnateria quark-alfa relevante en este regimen. ABSTIZACT:It has been conjectured that an quark, uncharged, spinless and colorless particle Cquark-alpha) could be stable at low pressures and temperatures even with respect to strange matter. We present in work tlie structure of stars including the effects of the appearance of quark-alpi' particles ii their outer layers. The internal structure is no longer from tlie center to the surface, but show a strange matter core, a solid and superfluid layers and a thin crust of normal matter at the surface. The normal matter surface allows tlie fon tion of a magnetosphere, whicl is to be tl place where pulsar emission occurs. A superfluid layer helps to explain tlie glitch , wlflch has been observed in . equation of state for quark-alpha matter relevant in regime is also discussed. Keq LA)OtL : ARY S - OF STATF - ?.ACT

  8. DA 495: An Aging Pulsar Wind Nebula

    NASA Astrophysics Data System (ADS)

    Kothes, R.; Landecker, T. L.; Reich, W.; Safi-Harb, S.; Arzoumanian, Z.

    2008-11-01

    We present a radio continuum study of the pulsar wind nebula (PWN) DA 495 (G65.7+1.2), including images of total intensity and linear polarization from 408 to 10550 MHz based on the Canadian Galactic Plane Survey and observations with the Effelsberg 100 m Radio Telescope. Removal of flux density contributions from a superimposed H II region and from compact extragalactic sources reveals a break in the spectrum of DA 495 at 1.3 GHz, with a spectral index α = - 0.45 +/- 0.20 below the break and α = - 0.87 +/- 0.10 above it (Sν propto να). The spectral break is more than 3 times lower in frequency than the lowest break detected in any other PWN. The break in the spectrum is likely the result of synchrotron cooling, and DA 495, at an age of ~20,000 yr, may have evolved from an object similar to the Vela X nebula, with a similarly energetic pulsar. We find a magnetic field of ~1.3 mG inside the nebula. After correcting for the resulting high internal rotation measure, the magnetic field structure is quite simple, resembling the inner part of a dipole field projected onto the plane of the sky, although a toroidal component is likely also present. The dipole field axis, which should be parallel to the spin axis of the putative pulsar, lies at an angle of ~50° east of the north celestial pole and is pointing away from us toward the southwest. The upper limit for the radio surface brightness of any shell-type supernova remnant emission around DA 495 is Σ1GHz ~ 5.4 × 10-23 W m-2 Hz-1 sr-1 (assuming a radio spectral index of α = - 0.5), lower than the faintest shell-type remnant known to date.

  9. Particle Acceleration in Dissipative Pulsar Magnetospheres

    NASA Technical Reports Server (NTRS)

    Kazanas, Z.; Kalapotharakos, C.; Harding, A.; Contopoulos, I.

    2012-01-01

    Pulsar magnetospheres represent unipolar inductor-type electrical circuits at which an EM potential across the polar cap (due to the rotation of their magnetic field) drives currents that run in and out of the polar cap and close at infinity. An estimate ofthe magnitude of this current can be obtained by dividing the potential induced across the polar cap V approx = B(sub O) R(sub O)(Omega R(sub O)/c)(exp 2) by the impedance of free space Z approx eq 4 pi/c; the resulting polar cap current density is close to $n {GJ} c$ where $n_{GJ}$ is the Goldreich-Julian (GJ) charge density. This argument suggests that even at current densities close to the GJ one, pulsar magnetospheres have a significant component of electric field $E_{parallel}$, parallel to the magnetic field, a condition necessary for particle acceleration and the production of radiation. We present the magnetic and electric field structures as well as the currents, charge densities, spin down rates and potential drops along the magnetic field lines of pulsar magnetospheres which do not obey the ideal MHD condition $E cdot B = 0$. By relating the current density along the poloidal field lines to the parallel electric field via a kind of Ohm's law $J = sigma E_{parallel}$ we study the structure of these magnetospheres as a function of the conductivity $sigma$. We find that for $sigma gg OmegaS the solution tends to the (ideal) Force-Free one and to the Vacuum one for $sigma 11 OmegaS. Finally, we present dissipative magnetospheric solutions with spatially variable $sigma$ that supports various microphysical properties and are compatible with the observations.

  10. Elementary wideband timing of radio pulsars

    SciTech Connect

    Pennucci, Timothy T.; Demorest, Paul B.; Ransom, Scott M. E-mail: pdemores@nrao.edu

    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.

  11. COSMIC-RAY POSITRONS FROM MILLISECOND PULSARS

    SciTech Connect

    Venter, C.; Kopp, A.; Büsching, I.; Harding, A. K.; Gonthier, P. L.

    2015-07-10

    Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 GeV. Fermi has also uncovered many new MSPs, impacting Galactic stellar population models. We investigate the contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters.

  12. Accretion onto Fast X-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Rappaport, S. A.; Fregeau, J. M.; Spruit, H.

    2004-01-01

    The recent emergence of a new class of accretion-powered, transient, millisecond X-ray pulsars presents some difficulties for the conventional picture of accretion onto rapidly rotating magnetized neutron stars and their spin behavior during outbursts. In particular, it is not clear that the standard paradigm can accommodate the wide range in M(i.e., approx. greater than a factor of 50) over which these systems manage to accrete and the high rate of spindown that the neutron stars exhibit in at least a number of cases. When the accretion rate drops sufficiently, the X-ray pulsar is said to become a "fast rotator," and in the conventional view, this is accompanied by a transition from accretion to "propellering," in which accretion ceases and the matter is ejected from the system. On the theoretical side, we note that this scenario for the onset of propellering cannot be entirely correct because it is not energetically self-consistent. We show that, instead, the transition is likely to take place through disks that combine accretion with spindown and terminate at the corotation radius. We demonstrate the existence of such disk solutions by modifying the Shakura-Sunyaev equations with a simple magnetic torque prescription. The solutions are completely analytic and have the same dependence on M and a (the viscosity parameter) as the original Shakura-Sunyaev solutions, but the radial profiles can be considerably modified, depending on the degree of fastness. We apply these results to compute the torques expected during the outbursts of the transient millisecond pulsars and find that we can explain the large spin-down rates that are observed for quite plausible surface magnetic fields of approx. 10(exp 90 G.

  13. Theory of pulsar magnetosphere and wind

    NASA Astrophysics Data System (ADS)

    Pétri, Jérôme

    2016-10-01

    > leptons or does it contain a non-negligible fraction of protons and/or ions? Is it almost entirely filled or mostly empty except for some small anecdotal plasma filled regions? Answers to these questions will strongly direct the description of the magnetosphere to seemingly contradictory results leading sometimes to inconsistencies. Nevertheless, accounts are given as to the latest developments in the theory of pulsar magnetospheres and winds, the existence of a possible electrosphere and physical insight obtained from related observational signatures of multi-wavelength pulsed emission.

  14. [Pulsar perimetry. A review and new results].

    PubMed

    Gonzalez de la Rosa, M; Gonzalez-Hernandez, M

    2013-02-01

    We present a review and update on Pulsar perimetry, which combines temporal frequency, contrast and spatial frequency stimuli. The effects of age, visual acuity, and learning on results are described. Data on threshold fluctuation, signal-to-noise ratio, and the possibility of reducing noise with filtering techniques are provided. We describe its dynamic range and the possibility of compensating for profound defects. Finally, we show the results obtained in normal patients and in those with ocular hypertension or initial glaucoma, as well as an analysis of glaucoma progression.

  15. Accretion powered X-ray pulsars

    NASA Technical Reports Server (NTRS)

    White, N. E.; Swank, J. H.; Holt, S. S.

    1982-01-01

    A unified description of the properties of 14 X-ray pulsars is presented and compared with the current theoretical understanding of these systems. The sample extends over six orders of magnitude in luminosity, with the only trend in the phase averaged spectra being that the lower luminosity systems appear to have less abrupt high energy cutoffs. There is no correlation of luminosity with power law index, high energy cutoff energy or iron line EW. Detailed pulse phase spectroscopy is given for five systems.

  16. Magnetospheric structure of rotation powered pulsars

    SciTech Connect

    Arons, J. California Univ., Livermore, CA . Inst. of Geophysics and Planetary Physics)

    1991-01-07

    I survey recent theoretical work on the structure of the magnetospheres of rotation powered pulsars, within the observational constraints set by their observed spindown, their ability to power synchrotron nebulae and their ability to produce beamed collective radio emission, while putting only a small fraction of their energy into incoherent X- and gamma radiation. I find no single theory has yet given a consistent description of the magnetosphere, but I conclude that models based on a dense outflow of pairs from the polar caps, permeated by a lower density flow of heavy ions, are the most promising avenue for future research. 106 refs., 4 figs., 2 tabs.

  17. Neutron star binaries, pulsars and burst sources

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.

    1981-01-01

    Unresolved issues involving neutron star binaries, pulsars, and burst sources are described. Attention is drawn to the types of observations most likely to resolve them. Many of these observations are likely to be carried out during the next decade by one or more missions that have been approved or proposed. Flux measurements with an imaging detector and broad-band spectroscopic studies in the energy range 30-150 keV are discussed. The need for soft X-ray and X-ray observations with an instrument which has arcminute angular resolution and an effective area substantially greater than of ROSAT or EXOSAT is also discussed.

  18. Pulsar population synthesis using palfa detections and pulsar search collaboratory discoveries including a wide DNS system and a nearby MSP

    NASA Astrophysics Data System (ADS)

    Swiggum, Joseph Karl

    Using the ensemble of detections from pulsar surveys, we can learn about the sizes and characteristics of underlying populations. In this thesis, I analyze results from the Pulsar Arecibo L-band Feed Array (PALFA) precursor and Green Bank Telescope 350 MHz Drift Scan surveys; I examine survey sensitivity to see how detections can inform pulsar population models, I look at new ways of including young scientists -- high school students -- in the discovery process and I present timing solutions for students' discoveries (including a nearby millisecond pulsar and a pulsar in a wide-orbit double neutron star system). The PALFA survey is on-going and uses the ALFA 7-beam receiver at 1400 MHz to search both inner and outer Galactic sectors visible from Arecibo (32° ?£? 77° and 168° ?£? 214°) close to the Galactic plane (|b| ? 5°) for pulsars. The PALFA precursor survey observed a subset of this region, (|b| ? 1°) and detected 45 pulsars, including one known millisecond pulsar (MSP) and 11 previously unknown, long-period (normal) pulsars. I assess the sensitivity of the PALFA precursor survey and use the number of normal pulsar and MSP detections to infer the size of each underlying Galactic population. Based on 44 normal pulsar detections and one MSP, we constrain each population size to 107,000+36,000-25,000 and 15,000 +85,000-6,000 respectively with 95% confidence. Based on these constraints, we predict yields for the full PALFA survey and find a deficiency in normal pulsar detections, possibly due to radio frequency interference and/or scintillation, neither of which are currently accounted for in population simulations. The GBT 350 MHz Drift Scan survey collected data in the summer of 2007 while the GBT was stationary, undergoing track replacement. Results discussed here come from ~20% of the survey data, which were processed and donated to the Pulsar Search Collaboratory (PSC). The PSC is a joint outreach program between WVU and NRAO, involving high school

  19. Properties of pulsars with short and long periods

    NASA Astrophysics Data System (ADS)

    Loginov, A. A.; Malov, I. F.

    2015-11-01

    A comparative analysis has been conducted for the timescale on which the observed radio emission of pulsars is switched off (nulling fraction), the polarization parameters, and the residual deviations in the pulse arrival times for pulsars with periods P >0.1 s and P <0.1 s. For the former group of pulsars, the greater the energy injected into the magnetosphere from internal layers of the neutron star, the smaller the nulling fraction; in the latter group, nullings are not observed at all. Mode switches are also observed only in pulsarswith long pulse-to-pulse intervals ( P >1 s), and in many objects they are correlatedwith the presence of nullings. The degree of polarization grows with decreasing period, and is systematically higher in objects with P <0.1 s than in long-period pulsars. The relative deviations of the pulse arrival times are, on average, appreciably smaller for pulsars with P >0.1 s. The observed differences in the parameters of pulsars with short and long periods can be understood if the radiation of pulsars with P <0.1 s is generated near the light cylinder.

  20. On Detecting Millisecond Pulsars at the Galactic Center

    NASA Astrophysics Data System (ADS)

    Macquart, Jean-Pierre; Kanekar, Nissim

    2015-06-01

    The lack of detected pulsars at the Galactic Center (GC) region is a long-standing mystery. We argue that the high stellar density in the central parsec around the GC is likely to result in a pulsar population dominated by millisecond pulsars (MSPs), similar to the situation in globular cluster environments. Earlier GC pulsar searches have been largely insensitive to such an MSP population, accounting for the lack of pulsar detections. We estimate the best search frequency for such an MSP population with present and upcoming broad-band radio telescopes for two possible scattering scenarios, the “weak-scattering” case suggested by the recent detection of a magnetar close to the GC, and the “strong-scattering” case, with the scattering screen located close to the GC. The optimal search frequencies are ≈8 GHz (weak-scattering) and ≈25 GHz (strong-scattering), for pulsars with periods 1-20 ms, assuming that GC pulsars have a luminosity distribution similar to that those in the rest of the Milky Way. We find that 10-30 hr integrations with the Very Large Array and the Green Bank Telescope would be sufficient to detect MSPs at the GC distance in the weak-scattering case. However, if the strong-scattering case is indeed applicable to the GC, observations with the full Square Kilometre Array would be needed to detect the putative MSP population.

  1. PRESTO: PulsaR Exploration and Search TOolkit

    NASA Astrophysics Data System (ADS)

    Ransom, Scott

    2011-07-01

    PRESTO is a large suite of pulsar search and analysis software. It was primarily designed to efficiently search for binary millisecond pulsars from long observations of globular clusters (although it has since been used in several surveys with short integrations and to process a lot of X-ray data as well). To date, PRESTO has discovered well over a hundred and fifty pulsars, including approximately 100 recycled pulsars, about 80 of which are in binaries. It is written primarily in ANSI C, with many of the recent routines in Python. Written with portability, ease-of-use, and memory efficiency in mind, it can currently handle raw data from the following pulsar machines or formats: PSRFITS search-format data (as from GUPPI at the GBT and the Mock Spectrometers at Arecibo)SPIGOT at the GBTMost Wideband Arecibo Pulsar Processor (WAPP) at AreciboThe Parkes and Jodrell Bank 1-bit filterbank formatsBerkeley-Caltech Pulsar Machine (BCPM) at the GBT (may it RIP...)8-bit filterbank format from SIGPROC (other formats will be added if required)A time series composed of single precision (i.e. 4-byte) floating point dataPhoton arrival times (or events) in ASCII or double-precision binary formats

  2. Prospects for Pulsar Studies with the GLAST Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2007-01-01

    The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST), due to launch in November 2007, will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered p ulsars. As the only presently known galactic GeV source class, pulsar s will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma-ray pulsar s, including millisecond pulsars, giving much better statistics for e lucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric partic le acceleration and radiation mechanisms, by comparing data with theo retical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all un identified EGRET sources, to possibly uncover more radio-quiet Geming a-like pulsars.

  3. Timing of 29 Pulsars Discovered in the PALFA Survey

    NASA Astrophysics Data System (ADS)

    Lyne, A. G.; Stappers, B. W.; Bogdanov, S.; Ferdman, R. D.; Freire, P. C. C.; Kaspi, V. M.; Knispel, B.; Lynch, R.; Allen, B.; Brazier, A.; Camilo, F.; Cardoso, F.; Chatterjee, S.; Cordes, J. M.; Crawford, F.; Deneva, J. S.; Hessels, J. W. T.; Jenet, F. A.; Lazarus, P.; van Leeuwen, J.; Lorimer, D. R.; Madsen, E.; McKee, J.; McLaughlin, M. A.; Parent, E.; Patel, C.; Ransom, S. M.; Scholz, P.; Seymour, A.; Siemens, X.; Spitler, L. G.; Stairs, I. H.; Stovall, K.; Swiggum, J.; Wharton, R. S.; Zhu, W. W.; Aulbert, C.; Bock, O.; Eggenstein, H.-B.; Fehrmann, H.; Machenschalk, B.

    2017-01-01

    We report on the discovery and timing observations of 29 distant long-period pulsars found in the ongoing Arecibo L-band Feed Array pulsar survey. Following discovery with the Arecibo Telescope, confirmation and timing observations of these pulsars over several years at Jodrell Bank Observatory have yielded high-precision positions and measurements of rotation and radiation properties. We have used multi-frequency data to measure the interstellar scattering properties of some of these pulsars. Most of the pulsars have properties that mirror those of the previously known pulsar population, although four show some notable characteristics. PSRs J1907+0631 and J1925+1720 are young and are associated with supernova remnants or plerionic nebulae: J1907+0631 lies close to the center of SNR G40.5‑0.5, while J1925+1720 is coincident with a high-energy Fermi γ-ray source. One pulsar, J1932+1500, is in a surprisingly eccentric, 199 day binary orbit with a companion having a minimum mass of 0.33 M⊙. Several of the sources exhibit timing noise, and two, PSRs J0611+1436 and J1907+0631, have both suffered large glitches, but with very different post-glitch rotation properties. In particular, the rotational period of PSR J0611+1436 will not recover to its pre-glitch value for about 12 years, a far greater recovery timescale than seen following any other large glitches.

  4. Imprints of relic gravitational waves on pulsar timing

    NASA Astrophysics Data System (ADS)

    Tong, Ming-Lei; Ding, Yong-Heng; Zhao, Cheng-Shi; Gao, Feng; Yan, Bao-Rong; Yang, Ting-Gao; Gao, Yu-Ping

    2016-03-01

    Relic gravitational waves (RGWs), a background originating during inflation, would leave imprints on pulsar timing residuals. This makes RGWs an important source for detection of RGWs using the method of pulsar timing. In this paper, we discuss the effects of RGWs on single pulsar timing, and quantitatively analyze the timing residuals caused by RGWs with different model parameters. In principle, if the RGWs are strong enough today, they can be detected by timing a single millisecond pulsar with high precision after the intrinsic red noises in pulsar timing residuals are understood, even though simultaneously observing multiple millisecond pulsars is a more powerful technique for extracting gravitational wave signals. We correct the normalization of RGWs using observations of the cosmic microwave background (CMB), which leads to the amplitudes of RGWs being reduced by two orders of magnitude or so compared to our previous works. We obtained new constraints on RGWs using recent observations from the Parkes Pulsar Timing Array, employing the tensor-to-scalar ratio r = 0.2 due to the tensor-type polarization observations of CMB by BICEP2 as a reference value, even though its reliability has been brought into question. Moreover, the constraints on RGWs from CMB and Big Bang nucleosynthesis will also be discussed for comparison.

  5. Binary Pulsar PSR 1913 + 16: Model for Its Origin.

    PubMed

    Van Horn, H M; Sofia, S; Savedoff, M P; Duthie, J G; Berg, R A

    1975-05-30

    The existing observational data for the binary pulsar PSR 1913 + 16 are sufficient to give a rather well-defined model for the system. On the basis of evolutionary considerations, the pulsar must be a neutron star near the upper mass limit of 1.2 solar masses (M.). The orbital inclination is probably high, i>/= 700, and the mass of the unseen companion probably lies close to the upper limit of the range 0.25 M. to 1.0 M.. The secondary cannot be a main sequence star and is probably a degenerate helium dwarf. At the 5.6-kiloparsec distance indicated by the dispersion measure, the magnetic dipole model gives an age of approximately 4 x 104 years, a rate of change of the pulsar period of P approximately 2 nanoseconds per day, and a surface magnetic field strength approximately (1/3) that of the Crab pulsar. The pulsar is fainter than an apparent magnitude V approximately + 26.5 and is at least approximately 80 times fainter than the Crab pulsar in the x-ray band. The companion star should be fainter than V approximately + 30, and a radio supernova remnant may be detectable near the position of the pulsar at a flux level of

  6. The Pulsar Quartet: Listening to a Galactic Symphony

    NASA Astrophysics Data System (ADS)

    Kiziltan, Bülent

    2014-06-01

    Pulsars are exotic dead stars that emit very regular radio pulses. These pulses are attributed to their regular rotation. Some pulsars are spinning fast enough that the audio equivalent waveform of their pulses fall within our hearing range. If human ears were tuned to radio waves it would have been possible to ‘hear’ these very compact stars. We produced the audio waveform of these pulsar signals and mapped them onto a frequency chart to find the corresponding musical notes. We use these ‘audible' pulsars like musical instruments in a symphony orchestra to play a full quartet. At the same time, an accompanying visual interface shows the realistic distribution of all pulsars in our own Galaxy. Pulsars shine as they play each note in the quartet with realistic brightening and subsequent dimming proportional to their rotational energies. This can serve as an educational tool at all levels to demonstrate many interesting aspects of stellar evolution and articulate an aesthetic connection of us with the cosmos. Interested in watching the light show while the Milky Way Pulsar Orchestra plays a quartet?

  7. Arecibo 1418 MHz Polarimetry and Morphological Classification of 95 Pulsars

    NASA Astrophysics Data System (ADS)

    Weitz, K. A.; Weisberg, J. M.; Dawson, B. R.; Despotes, J. T.; Morgan, J. J.; Zink, E. C.; Cordes, J. M.; Lundgren, S. C.; Backer, D. C.

    1995-12-01

    The classification of pulsars allows for the organization of groups of objects which share common features. These classes can then be studied for further correlations, providing insight into a variety of emission and evolutionary questions. Most classification systems are based on the analysis of polarized profiles over a wide frequency range. We gathered polarization data on over one hundred pulsars at 1418 MHz in fifteen observing sessions from 1989 to 1993, using the 305 meter Arecibo telescope. A 20 MHz digital multichannel correlation polarimeter was employed on-line. The multifrequency channels were then dedispersed before summing. All data for each individual pulsar were then calibrated and combined into one full Stokes parameter profile. This process led to polarized average pulse profiles for ninety-five of the pulsars. We used the Rankin (1983) system as the basis for our morphological classifications of the 95 pulsars. In Rankin's model, the frequency evolution of the polarized characteristics of each pulse component is assessed in order to distinguish core from hollow cone emission beams. We studied our 1418 MHz data and all other published polarimetry on each pulsar in order to determine the morphological classifications. We present the polarized profiles and discuss the morphological classifications for these 95 pulsars.

  8. ON DETECTING MILLISECOND PULSARS AT THE GALACTIC CENTER

    SciTech Connect

    Macquart, Jean-Pierre

    2015-06-01

    The lack of detected pulsars at the Galactic Center (GC) region is a long-standing mystery. We argue that the high stellar density in the central parsec around the GC is likely to result in a pulsar population dominated by millisecond pulsars (MSPs), similar to the situation in globular cluster environments. Earlier GC pulsar searches have been largely insensitive to such an MSP population, accounting for the lack of pulsar detections. We estimate the best search frequency for such an MSP population with present and upcoming broad-band radio telescopes for two possible scattering scenarios, the “weak-scattering” case suggested by the recent detection of a magnetar close to the GC, and the “strong-scattering” case, with the scattering screen located close to the GC. The optimal search frequencies are ≈8 GHz (weak-scattering) and ≈25 GHz (strong-scattering), for pulsars with periods 1–20 ms, assuming that GC pulsars have a luminosity distribution similar to that those in the rest of the Milky Way. We find that 10–30 hr integrations with the Very Large Array and the Green Bank Telescope would be sufficient to detect MSPs at the GC distance in the weak-scattering case. However, if the strong-scattering case is indeed applicable to the GC, observations with the full Square Kilometre Array would be needed to detect the putative MSP population.

  9. Towards robust detection of gravitational waves by pulsar timing

    NASA Astrophysics Data System (ADS)

    Cornish, Neil J.; Sampson, Laura

    2016-01-01

    Precision timing of highly stable milli-second pulsars is a promising technique for detecting very low frequency sources of gravitational waves. In any one pulsar, the gravitational wave signal appears as an additional source of timing noise, and it is only by considering the coherent response across a network of pulsars that the signal can be distinguished from other sources of noise. In the limit where there are many gravitational wave sources, or in the limit where there are many pulsars in the array, the waves produce a unique tensor correlation pattern that depends only on the angular separation of each pulsar pair. It is this distinct fingerprint that is used to search for gravitational waves using pulsar timing arrays. Here we consider how the prospects for detection are diminished when there are a finite number of signals and pulsars, which breaks the statistical isotropy of the timing array and of the gravitational wave sky. We also study the use of "sky-scrambles'' to break the signal correlations in the data as a way to increase confidence in a detection.

  10. Pulsar Wind Nebulae, Space Velocities and Supernova Remnant

    NASA Technical Reports Server (NTRS)

    2005-01-01

    The original proposal for this LTSA grant was for X-ray studies of pulsars, and especially pulsar wind nebulae and what they could tell us about pulsar properties, especially their space velocities. By any metric, this program has been very successful. No fewer than 14 papers on directly related topics (and several dozen more on related topics) have been published in refereed journals with the PI as lead or co-author, all observational results that have had significant impact on the field. These include the first X-ray detection of the "Duck" pulsar, a clear demonstration that estimated pulsar ages can be off by over an order of magnitude (via observations of the young supernova remnant G11.2-0.3) and the detection of the first pulsar wind nebula around a millisecond pulsar. These publications have also resulted in 4 press releases. Moreover, they also represent the thesis work of two PhD students at MIT (Froney Crawford and Mike Pivovaroff) and one postdoctoral fellow, Bryan Gaensler, now Assistant Professor at Harvard.

  11. Photovoltaic performances of Cu2-xTe sensitizer based on undoped and indium(3+)-doped TiO2 photoelectrodes and assembled counter electrodes.

    PubMed

    Srathongluan, Pornpimol; Kuhamaneechot, Rattanakorn; Sukthao, Prapatsawan; Vailikhit, Veeramol; Choopun, Supab; Tubtimtae, Auttasit

    2016-02-01

    Novel binary Cu2-xTe nanoparticles based on undoped and indium-doped TiO2 photoelectrodes were synthesized using a successive ionic layer adsorption and reaction (SILAR) technique as a sensitizer for liquid-junction solar cells. A larger diameter of TiO2 promoted a narrower energy band gap after indium doping, attributing to yield a broader absorption range of nanoparticle sensitizer due to the increasing amount of Cu2-xTe NPs on TiO2 surface. The atomic percentages showed the stoichiometric formation of Cu2Te incorporated in a Cu2-xTe structure. The best photovoltaic performance with the lower SILAR cycle, i.e., n=13 was performed after indium doping in both of carbon and Cu2S CEs and revealed that the efficiency of 0.73% under the radiant 100mW/cm(2) (AM 1.5G). The electrochemical impedance spectroscopy (EIS) was used to investigate the electrical properties via effect of material doping and counter electrodes with a lower charge-transfer resistance (Rct) and it was also found that the electron lifetime was improved after the sample doped with indium and assembled with carbon CE.

  12. MODELING THE JET KINEMATICS OF THE BLACK HOLE MICROQUASAR XTE J1550-564: A CONSTRAINT ON SPIN-ORBIT ALIGNMENT

    SciTech Connect

    Steiner, James F.; McClintock, Jeffrey E.

    2012-02-01

    Measurements of black hole spin made using the continuum-fitting method rely on the assumption that the inclination of the black hole's spin axis to our line of sight is the same as the orbital inclination angle i of the host binary system. The X-ray and radio jet data available for the microquasar XTE J1550-564 offer a rare opportunity to test this assumption. Following the work of others, we have modeled these data and thereby determined the inclination angle {theta} of the jet axis, which is presumed to be aligned with the black hole's spin axis. We find {theta} Almost-Equal-To 71 Degree-Sign and place an upper limit on the difference between the spin and orbital inclinations of |{theta} - i| < 12 Degree-Sign (90% confidence). Our measurement tests for misalignment along the line of sight while providing no constraint perpendicular to this plane. Our constraint on the misalignment angle supports the prediction that the spinning black hole in XTE J1550-564 has aligned itself with the orbital plane and provides support for the measurement of its spin via the continuum-fitting method. Our conclusions are based on a simple and reasonable model of a pair of symmetric jets propagating into a low-density cavity whose western wall is Almost-Equal-To 20% closer to XTE J1550-564 than its eastern wall.

  13. Electron Acceleration at Pulsar Wind Termination Shocks

    NASA Astrophysics Data System (ADS)

    Giacchè, S.; Kirk, John G.

    2017-02-01

    We study the acceleration of electrons and positrons at an electromagnetically modified, ultrarelativistic shock in the context of pulsar wind nebulae. We simulate the outflow produced by an obliquely rotating pulsar in proximity of its termination shock with a two-fluid code that uses a magnetic shear wave to mimic the properties of the wind. We integrate electron trajectories in the test-particle limit in the resulting background electromagnetic fields to analyze the injection mechanism. We find that the shock-precursor structure energizes and reflects a sizable fraction of particles, which becomes available for further acceleration. We investigate the subsequent first-order Fermi process sustained by small-scale magnetic fluctuations with a Monte Carlo code. We find that the acceleration proceeds in two distinct regimes: when the gyroradius {r}{{g}} exceeds the wavelength of the shear λ, the process is remarkably similar to first-order Fermi acceleration at relativistic, parallel shocks. This regime corresponds to a low-density wind that allows the propagation of superluminal waves. When {r}{{g}}< λ , which corresponds to the scenario of driven reconnection, the spectrum is softer.

  14. Low Frequency Interstellar Scattering and Pulsar Observations

    NASA Technical Reports Server (NTRS)

    Cordes, James M.

    1992-01-01

    Radio astronomy at frequencies from 2 to 30 MHz challenges time tested methods for extracting usable information from observations. One fundamental reason for this is that propagation effects due to the magnetoionic ionosphere, interplanetary medium, and interstellar matter (ISM) increase strongly with wavelength. The problems associated with interstellar scattering off of small scale irregularities in the electron density are addressed. What is known about interstellar scattering is summarized on the basis of high frequency observations, including scintillation and temporal broadening of pulsars and angular broadening of various galactic and extragalactic radio sources. Then those high frequency phenomena are addressed that are important or detectable at low frequencies. The radio sky becomes much simpler at low frequencies, most pulsars will not be seen as time varying sources, intensity variations will be quenched or will occur on time scales much longer than a human lifetime, and many sources will be angularly broadened and/or absorbed into the noise. Angular broadening measurements will help delineate the galactic distribution and power spectrum of small scale electron density irregularities.

  15. PULSAR OBSERVATIONS OF EXTREME SCATTERING EVENTS

    SciTech Connect

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

    2015-08-01

    Extreme scattering events (ESEs) in the interstellar medium (ISM) were first observed in regular flux measurements of compact extragalactic sources. They are characterized by a flux variation over a period of weeks, suggesting the passage of a “diverging plasma lens” across the line of sight (LOS). Modeling the refraction of such a lens indicates that the structure size must be of the order of AU and the electron density of the order of 10s of cm{sup −3}. Similar structures have been observed in measurements of pulsar intensity scintillation and group delay. Here we report observations of two ESEs, showing increases in both intensity scintillation and dispersion made with the Parkes Pulsar Timing Array. These allow us to make more complete models of the ESE, including an estimate of the “outer-scale” of the turbulence in the plasma lens. These observations clearly show that the ESE structure is fully turbulent on an AU scale. They provide some support for the idea that the structures are extended along the LOS, such as would be the case for a scattering shell. The dispersion measurements also show a variety of AU scale structures that would not be called ESEs, yet involve electron density variations typical of ESEs and likely have the same origin.

  16. Pulsar Emission Geometry and Accelerating Field Strength

    NASA Technical Reports Server (NTRS)

    DeCesar, Megan E.; Harding, Alice K.; Miller, M. Coleman; Kalapotharakos, Constantinos; Parent, Damien

    2012-01-01

    The high-quality Fermi LAT observations of gamma-ray pulsars have opened a new window to understanding the generation mechanisms of high-energy emission from these systems, The high statistics allow for careful modeling of the light curve features as well as for phase resolved spectral modeling. We modeled the LAT light curves of the Vela and CTA I pulsars with simulated high-energy light curves generated from geometrical representations of the outer gap and slot gap emission models. within the vacuum retarded dipole and force-free fields. A Markov Chain Monte Carlo maximum likelihood method was used to explore the phase space of the magnetic inclination angle, viewing angle. maximum emission radius, and gap width. We also used the measured spectral cutoff energies to estimate the accelerating parallel electric field dependence on radius. under the assumptions that the high-energy emission is dominated by curvature radiation and the geometry (radius of emission and minimum radius of curvature of the magnetic field lines) is determined by the best fitting light curves for each model. We find that light curves from the vacuum field more closely match the observed light curves and multiwavelength constraints, and that the calculated parallel electric field can place additional constraints on the emission geometry

  17. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Kramer, Michael; Possenti, Andrea; Manchester, Dick; Lyne, Andrew; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Stairs, Ingrid; Faulkner, Andrew; Eatough, Ralph; Lorimer, Duncan Ross

    2008-10-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. This session we have also incorporated P417, timing of a new class of pulsars, into this proposal. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 05:00-19:00 and the project should be scheduled within this interval.

  18. Gravitational waves from pulsars with measured braking index

    NASA Astrophysics Data System (ADS)

    de Araujo, José C. N.; Coelho, Jaziel G.; Costa, Cesar A.

    2016-09-01

    We study the putative emission of gravitational waves (GWs) in particular for pulsars with measured braking index. We show that the appropriate combination of both GW emission and magnetic dipole brakes can naturally explain the measured braking index, when the surface magnetic field and the angle between the magnetic dipole and rotation axes are time dependent. Then we discuss the detectability of these very pulsars by aLIGO and the Einstein Telescope. We call attention to the realistic possibility that aLIGO can detect the GWs generated by at least some of these pulsars, such as Vela, for example.

  19. On the Galactic Distributions of Radio Pulsars and Plasma Density

    NASA Astrophysics Data System (ADS)

    Ankay, A.; Yazgan, E.; Kutukcu, P.

    2016-12-01

    A brief review of distance measurement methods for some astronomical sources is presented. Galactic plasma density distribution as related to the distribution of radio pulsars is discussed and a method for constructing relations between dispersion measure and distance for Galactic radio pulsars in small solid angle intervals is described. Dispersion measure - distance relations for radio pulsars based on this approach in the Galactic longitude and latitude intervals of Δ l = 0°±2° and Δ b = 0°±2° are displayed and comparisons are made with the predictions of the two commonly used models.

  20. Pulsar Search Results from the Arecibo Remote Command Center

    NASA Astrophysics Data System (ADS)

    Garcia, Alejandro; Stovall, K.; Banaszak, S. A.; Becker, A.; Biwer, C. M.; Boehler, K.; Caballero, K.; Christy, B.; Cohen, S.; Crawford, F.; Cuellar, A.; Danford, A.; Dartez, L. P.; Day, D.; Flanigan, J. D.; Gonzalez, A.; Gustavson, K.; Handzo, E.; Hinojosa, J.; Jenet, F.; Kaplan, D. L.; Kayal, K.; Lommen, A. N.; Longoria, C.; Lopez, J.; Lunsford, G.; Mahany, N.; Martinez, J.; Mata, A.; Miller, A.; Murray, J.; Pankow, C.; Ramirez, I.; Reser, J.; Rojas, P.; Rohr, M.; Rolph, K.; Rose, C.; Rudnik, P.; Siemens, X.; Tellez, A.; Tillman, N.; Walker, A.; Wells, B. L.; Zermeno, A.; Consortium, GBNCC; Consortium, PALFA; Consortium, GBTDrift; Consortium, AO327

    2014-01-01

    The Arecibo Remote Command Center (ARCC) at the University of Texas at Brownsville, in collaboration with various Universities, is currently engaged in searching through ongoing radio telescope surveys for radio pulsars. ARCC is an integrated research/education program that allows students at the high school and undergraduate level to be directly involved with the research at the Arecibo and Green Bank radio telescopes. We discuss the progress of our search effort with PRESTO pulsar search pipelines. Web based tools have been developed so that high school, undergraduate, and graduate students could rank the pulsar candidates created by PRESTO pipelines. We describe these tools and present our current discoveries.

  1. Pulsar coherent de-dispersion system of Urumqi Observatory

    NASA Astrophysics Data System (ADS)

    Liyong, Liu; Esamdin, Ali; Jin, Zhang

    Pulsar coherent de-dispersion experiment has been carried by using the 25-m Nanshan radio telescope of Urumqi Observatory It uses a dual polarization receiver operating at 18cm and a VLBI back-end Mark5A The data processing system is based on a C program on Linux and a 4-node Beowulf cluster A high quality data acquisition system and a cluster with more processors are needed to build an on-line pulsar coherent de-dispersion system in future Key words Astronomical instrument Pulsar Coherent de-dispersion Parallel computing Cluster Mark5A

  2. Pulsar Coherent De-dispersion Experiment at Urumqi Observatory

    NASA Astrophysics Data System (ADS)

    Liu, Li-Yong; Ali, Esamdin; Zhang, Jin

    2006-12-01

    A Pulsar coherent de-dispersion experiment has been carried out using the 25-m Nanshan radio telescope at Urumqi Observatory. It uses a dual polarization receiver operating at 18 cm and a VLBI back-end: Mark5A, the minimum sampling time is 5 ns. The data processing system is based on a C program on Linux and a 4-node Beowulf cluster. A high quality data acquisition system and a cluster with more processors are needed to build an on-line pulsar coherent de-dispersion system in future. The main directions for the instrument are studies of pulsar timing, scintillation monitoring, etc.

  3. COHERENT NETWORK ANALYSIS FOR CONTINUOUS GRAVITATIONAL WAVE SIGNALS IN A PULSAR TIMING ARRAY: PULSAR PHASES AS EXTRINSIC PARAMETERS

    SciTech Connect

    Wang, Yan; Mohanty, Soumya D.; Jenet, Fredrick A.

    2015-12-20

    Supermassive black hole binaries are one of the primary targets of gravitational wave (GW) searches using pulsar timing arrays (PTAs). GW signals from such systems are well represented by parameterized models, allowing the standard Generalized Likelihood Ratio Test (GLRT) to be used for their detection and estimation. However, there is a dichotomy in how the GLRT can be implemented for PTAs: there are two possible ways in which one can split the set of signal parameters for semi-analytical and numerical extremization. The straightforward extension of the method used for continuous signals in ground-based GW searches, where the so-called pulsar phase parameters are maximized numerically, was addressed in an earlier paper. In this paper, we report the first study of the performance of the second approach where the pulsar phases are maximized semi-analytically. This approach is scalable since the number of parameters left over for numerical optimization does not depend on the size of the PTA. Our results show that for the same array size (9 pulsars), the new method performs somewhat worse in parameter estimation, but not in detection, than the previous method where the pulsar phases were maximized numerically. The origin of the performance discrepancy is likely to be in the ill-posedness that is intrinsic to any network analysis method. However, the scalability of the new method allows the ill-posedness to be mitigated by simply adding more pulsars to the array. This is shown explicitly by taking a larger array of pulsars.

  4. Application of Millisecond Pulsar Timing to the Long-Term Stability of Clock Ensembles

    NASA Technical Reports Server (NTRS)

    Foster, Roger S.; Matsakis, Demetrios N.

    1996-01-01

    We review the application of millisecond pulsars to define a precise long-term standard and positional reference system in a nearly inertial reference frame. We quantify the current timing precision of the best millisecond pulsars and define the required precise time and time interval (PTTI) accuracy and stability to enable time transfer via pulsars. Pulsars may prove useful as independent standards to examine decade-long timing stability and provide an independent natural system within which to calibrate any new, perhaps vastly improved atomic time scale. Since pulsar stability appears to be related to the lifetime of the pulsar, the new millisecond pulsar J173+0747 is projected to have a 100-day accuracy equivalent to a single HP5071 cesium standard. Over the last five years, dozens of new millisecond pulsars have been discovered. A few of the new millisecond pulsars may have even better timing properties.

  5. High-precision timing of 42 millisecond pulsars with the European Pulsar Timing Array

    NASA Astrophysics Data System (ADS)

    Desvignes, G.; Caballero, R. N.; Lentati, L.; Verbiest, J. P. W.; Champion, D. J.; Stappers, B. W.; Janssen, G. H.; Lazarus, P.; Osłowski, S.; Babak, S.; Bassa, C. G.; Brem, P.; Burgay, M.; Cognard, I.; Gair, J. R.; Graikou, E.; Guillemot, L.; Hessels, J. W. T.; Jessner, A.; Jordan, C.; Karuppusamy, R.; Kramer, M.; Lassus, A.; Lazaridis, K.; Lee, K. J.; Liu, K.; Lyne, A. G.; McKee, J.; Mingarelli, C. M. F.; Perrodin, D.; Petiteau, A.; Possenti, A.; Purver, M. B.; Rosado, P. A.; Sanidas, S.; Sesana, A.; Shaifullah, G.; Smits, R.; Taylor, S. R.; Theureau, G.; Tiburzi, C.; van Haasteren, R.; Vecchio, A.

    2016-05-01

    We report on the high-precision timing of 42 radio millisecond pulsars (MSPs) observed by the European Pulsar Timing Array (EPTA). This EPTA Data Release 1.0 extends up to mid-2014 and baselines range from 7-18 yr. It forms the basis for the stochastic gravitational-wave background, anisotropic background, and continuous-wave limits recently presented by the EPTA elsewhere. The Bayesian timing analysis performed with TEMPONEST yields the detection of several new parameters: seven parallaxes, nine proper motions and, in the case of six binary pulsars, an apparent change of the semimajor axis. We find the NE2001 Galactic electron density model to be a better match to our parallax distances (after correction from the Lutz-Kelker bias) than the M2 and M3 models by Schnitzeler. However, we measure an average uncertainty of 80 per cent (fractional) for NE2001, three times larger than what is typically assumed in the literature. We revisit the transverse velocity distribution for a set of 19 isolated and 57 binary MSPs and find no statistical difference between these two populations. We detect Shapiro delay in the timing residuals of PSRs J1600-3053 and J1918-0642, implying pulsar and companion masses m_p=1.22_{-0.35}^{+0.5} M_{⊙}, m_c = 0.21_{-0.04}^{+0.06} M_{⊙} and m_p=1.25_{-0.4}^{+0.6} M_{⊙}, m_c = 0.23_{-0.05}^{+0.07} M_{⊙}, respectively. Finally, we use the measurement of the orbital period derivative to set a stringent constraint on the distance to PSRs J1012+5307 and J1909-3744, and set limits on the longitude of ascending node through the search of the annual-orbital parallax for PSRs J1600-3053 and J1909-3744.

  6. ARECIBO PULSAR SURVEY USING ALFA: PROBING RADIO PULSAR INTERMITTENCY AND TRANSIENTS

    SciTech Connect

    Deneva, J. S.; Cordes, J. M.; McLaughlin, M. A.; Lorimer, D. R.; Edel, S.; Kondratiev, V. I.; Nice, D. J.; Crawford, F.; Bhat, N. D. R.; Camilo, F.; Champion, D. J.; Freire, P. C. C.; Hessels, J. W. T.; Jenet, F. A.; Kasian, L.; Kaspi, V. M.; Lazarus, P.; Stairs, I. H.; Kramer, M.; Ransom, S. M.

    2009-10-01

    We present radio transient search algorithms, results, and statistics from the ongoing Arecibo Pulsar ALFA (PALFA) survey of the Galactic plane. We have discovered seven objects through a search for isolated dispersed pulses. All of these objects are Galactic and have measured periods between 0.4 and 4.7 s. One of the new discoveries has a duty cycle of 0.01%, smaller than that of any other radio pulsar. We discuss the impact of selection effects on the detectability and classification of intermittent sources, and compare the efficiencies of periodicity and single-pulse (SP) searches for various pulsar classes. For some cases we find that the apparent intermittency is likely to be caused by off-axis detection or a short time window that selects only a few bright pulses and favors detection with our SP algorithm. In other cases, the intermittency appears to be intrinsic to the source. No transients were found with DMs large enough to require that they originate from sources outside our Galaxy. Accounting for the on-axis gain of the ALFA system, as well as the low gain but large solid-angle coverage of far-out sidelobes, we use the results of the survey so far to place limits on the amplitudes and event rates of transients of arbitrary origin.

  7. The Structure and Evolution of Pulsar Wind Nebulae

    NASA Astrophysics Data System (ADS)

    Slane, Patrick O.

    2010-01-01

    The extended nebulae formed as pulsar winds expand into their surroundings provide information about the composition of the winds, the injection history from the host pulsar, and the material into which the nebulae are expanding. Observations from across the electromagnetic spectrum provide constraints on the evolution of the nebulae, the density and composition of the surrounding ejecta, the geometry of the central engines, and the long-term fate of the energetic particles produced in these systems. Such observations reveal the presence of jets and wind termination shocks, time-varying compact emission structures, shocked supernova ejecta, and newly formed dust. Here I provide a broad overview of the structure of pulsar wind nebulae, with specific examples from observations extending from the radio band to very high energy gamma-rays that demonstrate our ability to constrain the history and ultimate fate of the energy released in the spin-down of young pulsars.

  8. AB INITIO PULSAR MAGNETOSPHERE: THE ROLE OF GENERAL RELATIVITY

    SciTech Connect

    Philippov, Alexander A.; Cerutti, Benoit; Spitkovsky, Anatoly; Tchekhovskoy, Alexander

    2015-12-20

    It has recently been demonstrated that self-consistent particle-in-cell simulations of low-obliquity pulsar magnetospheres in flat spacetime show weak particle acceleration and no pair production near the poles. We investigate the validity of this conclusion in a more realistic spacetime geometry via general-relativistic particle-in-cell simulations of the aligned pulsar magnetosphere with pair formation. We find that the addition of the frame-dragging effect makes the local current density along the magnetic field larger than the Goldreich–Julian value, which leads to unscreened parallel electric fields and the ignition of a pair cascade. When pair production is active, we observe field oscillations in the open field bundle, which could be related to pulsar radio emission. We conclude that general-relativistic effects are essential for the existence of the pulsar mechanism in low-obliquity rotators.

  9. JPL pulsar timing observations. IV - Excess phase noise

    NASA Technical Reports Server (NTRS)

    Downs, G. S.; Krause-Polstorff, J.

    1986-01-01

    Previously published tables of geocentric arrival times for 24 pulsars covering a 12 year span are extended here to 14.5 years. The list of pulsars is extended by nine, most of which were observed for about 4 years. Known positins of these new objects are confirmed, and limits on the proper motions are obtained. Large phase excursions in PSR 0525 + 21 are found. The orbital parameters of the binary pulsar 0820 + 02 are tentatively confirmed. Short-term timing noise in excess of that expected from receiver considerations alone is established. Variations in the timing residuals for the original 24 pulsars are analyzed for correlations with other observable parameters. Little significant correlation with changes in pulse shape or energy or with the drift correction is found on time scales of 500 pulses or longer.

  10. Pulsar H(alpha) Bowshocks probe Neutron Star Physics

    NASA Astrophysics Data System (ADS)

    Romani, Roger W.

    2014-08-01

    We propose a KOALA/AAOmega study of southern pulsar bow shocks. These rare, Balmer-dominated, non-radiative shocks provide an ideal laboratory to study the interaction of the relativistic pulsar wind with the ISM. We will cover H(alpha) at high spectral resolution to measure the kinematics of the upstream ISM and the post-shock flow, while the blue channel measures the Balmer decrement and probes for a faint cooling component. These data, with MHD models, allow us to extract the 3D flow geometry and the orientation and asymmetry of the pulsar wind. These data can also measure the pulsar spindown power, thus estimating the neutron star moment of inertia and effecting a fundamental test of dense matter physics.

  11. The Effect of Geometrical Factors on Pulsar Rotation Parameters

    NASA Astrophysics Data System (ADS)

    Li, L.; Wang, G. L.; Guo, L.

    2016-09-01

    This paper presents a detailed investigation of the effects of geometrical factors on pulsar rotation parameters, such as the Earth orientation parameters, precession-nutation model, relative velocity, relative radial acceleration, and planetary ephemeris error. We derive the magnitude of the effect of secular variations in the observed periods and period derivatives, assuming that pulsars have typical values of the parameters. The effects of Earth orientation parameters and precession-nutation model are neglected at the current accuracy level of observation. Furthermore, the planetary ephemeris error has a marginal effect on the pulsar period parameters, and the effect of relative radial velocity is also ignored. However, the transverse velocity and relative radial acceleration stand as the likely sources of period derivative, especially for millisecond pulsars, where they may dominate the observed value of period derivative.

  12. Chandler wobble and free core nutation of single pulsar

    NASA Astrophysics Data System (ADS)

    Gusev, A.

    2011-10-01

    PSR B1828-11 has long-term, highly periodic and correlated variations pulse shape and of the rate of slow-down with period variations approximately 1000, 500 and 250 days (Stairs et al., 2000). There are three potential explanations of pulses time-of-arrival from pulsar concerned with the interior of the neutron star, planetary bodies, free precession and nutation. We use the Hamiltonian canonical method of Getino et al. (1999) for the dynamically symmetrical pulsar consisting of the rigid crust, elliptical liquid outer core and solid inner core of PSR B1828-11. Correctly extending theory of differential rotation of a pulsar, we investigated dependence on Chandler wobble period, Inner Chandler Wobble, retrograde Free Core Nutation and prograde Free Inner Core Nutation from ellipticity of inner crystal core, outer liquid core and total pulsar.

  13. Future Gamma-Ray Observations of Pulsars and their Environments

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2006-01-01

    Pulsars and pulsar wind nebulae seen at gamma-ray energies offer insight into particle acceleration to very high energies under extreme conditions. Pulsed emission provides information about the geometry and interaction processes in the magnetospheres of these rotating neutron stars, while the pulsar wind nebulae yield information about high-energy particles interacting with their surroundings. During the next decade, a number of new and expanded gamma-ray facilities will become available for pulsar studies, including Astro-rivelatore Gamma a Immagini LEggero (AGILE) and Gamma-ray Large Area Space Telescope (GLAST) in space and a number of higher-energy ground-based systems. This review describes the capabilities of such observatories to answer some of the open questions about the highest-energy processes involving neutron stars.

  14. Timing and searching millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew; van Straten, Willem

    2010-04-01

    Timing the dozen pulsars discovered in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the eclipse region and the orbital secular evolution). We also request time for performing observations for a new deeper than ever search for millisecond pulsars in a subset of suitable clusters. This revamped search (as well as the requested timing observations) will exploit the new back-ends (APSR and DFB4) now available at Parkes.

  15. Timing and searching millisecond pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Kramer, Michael; Sarkissian, John; Lyne, Andrew; Burgay, Marta; Corongiu, Alessandro; Camilo, Fernando; Bailes, Matthew

    2009-10-01

    Timing the dozen pulsars discovered in P303 is ensuring high quality results: (a) the peculiarities (in position or projected acceleration) of all the 5 millisecond pulsars in NGC6752 suggested the presence of non thermal dynamics in the core, perhaps due to black-holes of intermediate mass; (b) the eclipsing pulsar in NGC6397 is a stereotype for studying the late evolution of exotic binaries. We propose to continue our timing project focusing mostly on NGC6752 at 20cm (in order to measure additional parameters useful to constrain the existence of a black-hole) and NGC6397 at 10cm (for studying the eclipse region and the orbital secular evolution). We also request time for performing pilot observations for a new deeper than ever search for millisecond pulsars in a subset of suitable clusters. This revamped search (as well as the requested timing observations) will exploit the new back-ends (APSR and DFB4) now available at Parkes.

  16. Binary pulsar evolution: unveiled links and new species

    NASA Astrophysics Data System (ADS)

    Possenti, Andrea

    2013-03-01

    In the last years a series of blind and/or targeted pulsar searches led to almost triple the number of known binary pulsars in the galactic field with respect to a decade ago. The focus will be on few outliers, which are emerging from the average properties of the enlarged binary pulsar population. Some of them may represent the long sought missing links between two kinds of neutron star binaries, while others could represent the stereotype of new groups of binaries, resulting from an evolutionary path which is more exotic than those considered until recently. In particular, a new class of binaries, which can be dubbed Ultra Low Mass Binary Pulsars (ULMBPs), is emerging from recent data.

  17. Is the Enigma of Pulsar Radio Emission Solved?

    NASA Astrophysics Data System (ADS)

    Gil, Janusz A.; Melikidze, George I.

    2011-08-01

    An intriguing paper has recently been published claiming that the long-sought Rosetta Stone needed to decipher the nature of pulsar radio emission has been finally identified as the bifurcated features in averaged pulsar profiles. The authors argued that highly symmetric bifurcated features observed in PSR J1012+5307 and other pulsars are produced by a split-fan beams of extraordinary-mode curvature radiation emitted by thin streams of sources conducted by a very narrow bundles of magnetic field lines. We examined the arguments leading to such a profound conclusion and found at least one fatal flaw. Using an elementary pulsar physics we showed that there is not enough energy to power the bifurcated feature in J1012+5307 within a split-fan beams model. If the source streams are indeed so thin that their emission can reveal the signatures of elementary radiation mechanism, then the energy deficit reaches several orders of magnitude.

  18. An axisymmetric magnetohydrodynamic model for the Crab pulsar wind bubble

    NASA Technical Reports Server (NTRS)

    Begelman, Mitchell C.; Li, Zhi-Yun

    1992-01-01

    We extend Kennel and Coroniti's (1984) spherical magnetohydrodynamic models for the Crab Nebula to include the pinching effect of the toroidal magnetic field. Since the bulk nebular flow is likely to be very submagnetosonic, a quasi-static treatment is possible. We show that the pinching effect can be responsible for the observed elongation of the pulsar wind bubble, as indicated by the surface brightness contours of optical synchrotron radiation. From the observed elongation we estimate a value for sigma, the ratio of Poynting flux to plasma kinetic energy flux in the free pulsar wind, which is consistent with previous results from spherical models. Using the inferred magnetic field configuration inside the pulsar wind bubble, combined with the observed dimensions of the X-ray nebula, we are able to constrain the particle distribution function. We conclude that, for a power-law injection function, the maximum energy has to be much larger in the pulsar equatorial region than in the polar region.

  19. Pulsar timing arrays: the promise of gravitational wave detection.

    PubMed

    Lommen, Andrea N

    2015-12-01

    We describe the history, methods, tools, and challenges of using pulsars to detect gravitational waves. Pulsars act as celestial clocks detecting gravitational perturbations in space-time at wavelengths of light-years. The field is poised to make its first detection of nanohertz gravitational waves in the next 10 years. Controversies remain over how far we can reduce the noise in the pulsars, how many pulsars should be in the array, what kind of source we will detect first, and how we can best accommodate our large bandwidth systems. We conclude by considering the important question of how to plan for a post-detection era, beyond the first detection of gravitational waves.

  20. Nanohertz gravitational wave searches with interferometric pulsar timing experiments.

    PubMed

    Tinto, Massimo

    2011-05-13

    We estimate the sensitivity to nano-Hertz gravitational waves of pulsar timing experiments in which two highly stable millisecond pulsars are tracked simultaneously with two neighboring radio telescopes that are referenced to the same timekeeping subsystem (i.e., "the clock"). By taking the difference of the two time-of-arrival residual data streams we can exactly cancel the clock noise in the combined data set, thereby enhancing the sensitivity to gravitational waves. We estimate that, in the band (10(-9)-10(-8))  Hz, this "interferometric" pulsar timing technique can potentially improve the sensitivity to gravitational radiation by almost 2 orders of magnitude over that of single-telescopes. Interferometric pulsar timing experiments could be performed with neighboring pairs of antennas of the NASA's Deep Space Network and the forthcoming large arraying projects.

  1. Pulsars in the Classroom: Suggested Exercises for Lab or Homework

    ERIC Educational Resources Information Center

    Gordon, Kurtiss J.

    1978-01-01

    Exercises for introductory to intermediate level college students are proposed. Observations of pulsars can be used to illustrate the phenomena of dispersion and Faraday rotation of radio waves, and to illustrate the differential rotation of the galaxy. (BB)

  2. An eccentric binary millisecond pulsar in the galactic plane.

    PubMed

    Champion, David J; Ransom, Scott M; Lazarus, Patrick; Camilo, Fernando; Bassa, Cees; Kaspi, Victoria M; Nice, David J; Freire, Paulo C C; Stairs, Ingrid H; van Leeuwen, Joeri; Stappers, Ben W; Cordes, James M; Hessels, Jason W T; Lorimer, Duncan R; Arzoumanian, Zaven; Backer, Don C; Bhat, N D Ramesh; Chatterjee, Shami; Cognard, Ismaël; Deneva, Julia S; Faucher-Giguère, Claude-André; Gaensler, Bryan M; Han, Jinlin; Jenet, Fredrick A; Kasian, Laura; Kondratiev, Vlad I; Kramer, Michael; Lazio, Joseph; McLaughlin, Maura A; Venkataraman, Arun; Vlemmings, Wouter

    2008-06-06

    Binary pulsar systems are superb probes of stellar and binary evolution and the physics of extreme environments. In a survey with the Arecibo telescope, we have found PSR J1903+0327, a radio pulsar with a rotational period of 2.15 milliseconds in a highly eccentric (e = 0.44) 95-day orbit around a solar mass (M(middle dot in circle)) companion. Infrared observations identify a possible main-sequence companion star. Conventional binary stellar evolution models predict neither large orbital eccentricities nor main-sequence companions around millisecond pulsars. Alternative formation scenarios involve recycling a neutron star in a globular cluster, then ejecting it into the Galactic disk, or membership in a hierarchical triple system. A relativistic analysis of timing observations of the pulsar finds its mass to be 1.74 +/- 0.04 M solar symbol, an unusually high value.

  3. Pulsar Pair Cascades in a Distorted Magnetic Dipole Field

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alex G.

    2010-01-01

    We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap (PC), we derive the accelerating electric field above the PC in space-charge-limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the PC and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P-P-dot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons.

  4. Finding (Or Not) New Gamma-Ray Pulsars with GLAST

    SciTech Connect

    Ransom, Scott M.; /NRAO, Charlottesville

    2011-11-29

    Young energetic pulsars will likely be the largest class of Galactic sources observed by GLAST, with many hundreds detected. Many will be unknown as radio pulsars, making pulsation detection dependent on radio and/or x-ray observations or on blind periodicity searches of the gamma-rays. Estimates for the number of pulsars GLAST will detect in blind searches have ranged from tens to many hundreds. I argue that the number will be near the low end of this range, partly due to observations being made in a scanning as opposed to a pointing mode. This paper briefly reviews how blind pulsar searches will be conducted using GLAST, what limits these searches, and how the computations and statistics scale with various parameters.

  5. An Eccentric Binary Millisecond Pulsar in the Galactic Plane

    NASA Technical Reports Server (NTRS)

    Champion, David J.; Ransom, Scott M.; Lazarus, Patrick; Camilo, Fernando; Bassa, Cess; Kaspi, Victoria M.; Nice, David J.; Freire, Paulo C. C.; Stairs, Ingrid H.; vanLeeuwen, Joeri; Stappers, Ben W.; Cordes, James M.; Hessels, Jason W. T.; Lorimer, Duncan R.; Arzoumanian, Zaven; Backer, Don C.; Bhat, N. D. Ramesh; Chatterjee, Shami; Cognard, Ismael; Deneva, Julia S.; Faucher-Giguere, Claude-Andre; Gaensler, Bryan M.; Han, JinLin; Jenet, Fredrick A.; Kasian, Laura

    2008-01-01

    Binary pulsar systems are superb probes of stellar and binary evolution and the physics of extreme environments. In a survey with the Arecibo telescope, we have found PSR J1903+0327, a radio pulsar with a rotational period of 2.15 milliseconds in a highly eccentric (e = 0.44) 95-day orbit around a solar mass (M.) companion. Infrared observations identify a possible main-sequence companion star. Conventional binary stellar evolution models predict neither large orbital eccentricities nor main-sequence companions around millisecond pulsars. Alternative formation scenarios involve recycling a neutron star in a globular cluster, then ejecting it into the Galactic disk, or membership in a hierarchical triple system. A relativistic analysis of timing observations of the pulsar finds its mass to be 1.74 +/- 0.04 Solar Mass, an unusually high value.

  6. GLAST LAT And Pulsars: What Do We Learn from Simulations?

    SciTech Connect

    Razzano, Massimiliano; Harding, Alice K.; /NASA, Goddard

    2007-10-24

    Gamma-ray pulsars are among the best targets for the Large Area Telescope (LAT) aboard the GLAST mission. The higher sensitivity, time and energy resolution of the LAT will provide data of fundamental importance to understand the physics of these fascinating objects. Powerful tools for studying the LAT capabilities for pulsar science are the simulation programs developed within the GLAST Collaboration. Thanks to these simulations it is possible to produce a detailed distribution of gamma-ray photons in energy and phase that can be folded through the LAT Instrument Response Functions (IRFs). Here we present some of the main interesting results from the simulations developed to study the discovery potential of the LAT. In particular we will focus on the capability of the LAT to discover new radio-loud gamma-ray pulsars, on the discrimination between Polar Cap and Outer Gap models, and on the LAT pulsar sensitivity.

  7. Spin-down of radio millisecond pulsars at genesis.

    PubMed

    Tauris, Thomas M

    2012-02-03

    Millisecond pulsars are old neutron stars that have been spun up to high rotational frequencies via accretion of mass from a binary companion star. An important issue for understanding the physics of the early spin evolution of millisecond pulsars is the impact of the expanding magnetosphere during the terminal stages of the mass-transfer process. Here, I report binary stellar evolution calculations that show that the braking torque acting on a neutron star, when the companion star decouples from its Roche lobe, is able to dissipate >50% of the rotational energy of the pulsar. This effect may explain the apparent difference in observed spin distributions between x-ray and radio millisecond pulsars and help account for the noticeable age discrepancy with their young white dwarf companions.

  8. Pulsar timing sensitivity to very-low-frequency gravitational waves

    SciTech Connect

    Jenet, Fredrick A.; Armstrong, J. W.; Tinto, Massimo

    2011-04-15

    We compute the sensitivity, constrained by instrumental, propagation, and other fundamental noises, of pulsar timing to very-low-frequency gravitational waves (GWs). Reaching predicted GW signal strengths will require suppression of time-of-arrival fluctuations caused by interstellar plasma turbulence and a reduction of white rms timing noise to < or approx. 100 ns. Assuming negligible intrinsic pulsar rotational noise, perfect time transfer from time standard to observatory, and stable pulse profiles, the resulting single-pulsar signal-to-noise ratio=1 sensitivity is limited by terrestrial time standards at h{sub rms}{approx}2x10{sup -16} [f/ (1 cycle/year)]-1/2 for f<3x10{sup -8} Hz, where f is the Fourier frequency and a bandwidth of 1 cycle/(10 years) is assumed. Since this sensitivity is comparable to predicted GW signal levels, a reliable detection will require substantial signal-to-noise ratio improvement via pulsar timing array.

  9. Spin-Down of Radio Millisecond Pulsars at Genesis

    NASA Astrophysics Data System (ADS)

    Tauris, Thomas M.

    2012-02-01

    Millisecond pulsars are old neutron stars that have been spun up to high rotational frequencies via accretion of mass from a binary companion star. An important issue for understanding the physics of the early spin evolution of millisecond pulsars is the impact of the expanding magnetosphere during the terminal stages of the mass-transfer process. Here, I report binary stellar evolution calculations that show that the braking torque acting on a neutron star, when the companion star decouples from its Roche lobe, is able to dissipate >50% of the rotational energy of the pulsar. This effect may explain the apparent difference in observed spin distributions between x-ray and radio millisecond pulsars and help account for the noticeable age discrepancy with their young white dwarf companions.

  10. Magnetic pair creation transparency in gamma-ray pulsars

    SciTech Connect

    Story, Sarah A.; Baring, Matthew G. E-mail: baring@rice.edu

    2014-07-20

    Magnetic pair creation, γ → e {sup +} e {sup –}, has been at the core of radio pulsar paradigms and central to polar cap models of gamma-ray pulsars for over three decades. The Fermi gamma-ray pulsar population now exceeds 140 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 population characteristics well established is the common occurrence of exponential turnovers in their spectra 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. By demanding insignificant photon attenuation precipitated by such single-photon pair creation, the energies of these turnovers for Fermi pulsars can be used to compute lower bounds for the typical altitude of GeV band emission. This paper explores such pair transparency constraints below the turnover energy and updates earlier altitude bound determinations that have been deployed in various Fermi pulsar papers. For low altitude emission locales, general relativistic influences are found to be important, increasing cumulative opacity, shortening the photon attenuation lengths, and also reducing the maximum energy that permits escape of photons from a neutron star magnetosphere. Rotational aberration influences are also explored, and are found to be small at low altitudes, except near the magnetic pole. The analysis presented in this paper clearly demonstrates that including near-threshold physics in the pair creation rate is essential to deriving accurate attenuation lengths and escape energies. The altitude bounds are typically in the range of 2-7 stellar radii for the young Fermi pulsar population, and provide key information on the emission altitude in radio quiet pulsars that do not possess double-peaked pulse profiles. The bound for the Crab pulsar is at a much higher altitude, with the

  11. Characterization of the Crab Pulsar's Timing Noise

    NASA Technical Reports Server (NTRS)

    Scott, D. M.; Finger, M. H.; Wilson, C. A.

    2003-01-01

    We present a power spectral analysis of the Crab pulsar's timing noise, mainly using radio measurements from Jodrell Bank taken over the period 1982-1989, an interval bounded by sparse data sampling and a large glitch. The power spectral analysis is complicated by nonuniform data sampling and the presence of a steep red power spectrum that can distort power spectra measurement by causing severe power 'leakage'. We develop a simple windowing method for computing red noise power spectra of uniformly sampled data sets and test it on Monte Carlo generated sample realizations of red power-law noise. We generalize time-domain methods of generating power-law red noise with even integer spectral indices to the case of noninteger spectral indices. The Jodrell Bank pulse phase residuals are dense and smooth enough that an interpolation onto a uniform time series is possible. A windowed power spectrum is computed revealing a periodic or nearly periodic component with a period of 568 +/- 10 days and a l/f(exp 3) power-law noise component in pulse phase with a noise strength S(sub infinity)=(1.24 +/- 0.067) x 10(exp 16) cycles(exp 2)/sec(exp 2) over the analysis frequency range f=0.003- 0.1 cycles/day. This result deviates from past analyses which characterized the pulse phase timing residuals as either l/f(sub 4) power-law noise or a quasiperiodic process. The analysis was checked using the Deeter polynomial method of power spectrum estimation that was developed for the case of nonuniform sampling, but has lower spectral resolution. The timing noise is consistent with a torque noise spectrum rising with analysis frequency as f implying blue torque noise, a result not predicted by current models of pulsar timing noise. If the periodic or nearly periodic component is due to a binary companion, we find a mass function f(M) = (6.8 +/- 2.4) x 10(exp -16) solar mass and a companion mass, M(sub c) is greater than or equal to 3.2 solar mass assuming a Crab pulsar mass of 1.4 solar

  12. An x-ray nebula associated with the millisecond pulsar B1957+20.

    PubMed

    Stappers, B W; Gaensler, B M; Kaspi, V M; van der Klis, M; Lewin, W H G

    2003-02-28

    We have detected an x-ray nebula around the binary millisecond pulsar B1957+20. A narrow tail, corresponding to the shocked pulsar wind, is seen interior to the known Halpha bow shock and proves the long-held assumption that the rotational energy of millisecond pulsars is dissipated through relativistic winds. Unresolved x-ray emission likely represents the shock where the winds of the pulsar and its companion collide. This emission indicates that the efficiency with which relativistic particles are accelerated in the postshock flow is similar to that for young pulsars, despite the shock proximity and much weaker surface magnetic field of this millisecond pulsar.

  13. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Eatough, Ralph; Possenti, Andrea; Manchester, Dick; Kramer, Michael; Lyne, Andrew; Hobbs, George; Burgay, Marta; Camilo, Fernando; Stairs, Ingrid; Keith, Michael; Lorimer, Duncan Ross; Jaroenjittichai, Phrudth

    2010-04-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 10:00-19:00 and the project should be scheduled within this interval.

  14. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Eatough, Ralph; Possenti, Andrea; Manchester, Dick; Kramer, Michael; Lyne, Andrew; Hobbs, George; Burgay, Marta; Camilo, Fernando; Stairs, Ingrid; Keith, Michael; Lorimer, Duncan Ross; Jaroenjittichai, Phrudth

    2009-10-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 10:00-19:00 and the project should be scheduled within this interval.

  15. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Eatough, Ralph; Possenti, Andrea; Manchester, Dick; Verbiest, Joris P. W.; Kramer, Michael; Lyne, Andrew; Hobbs, George; Burgay, Marta; Camilo, Fernando; Stairs, Ingrid; Keith, Michael; Lorimer, Duncan Ross

    2010-10-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 10:00-19:00 and the project should be scheduled within this interval.

  16. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Kramer, Michael; Possenti, Andrea; Manchester, Dick; Lyne, Andrew; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Camilo, Fernando; Stairs, Ingrid; Faulkner, Andrew; Lorimer, Duncan Ross

    2007-04-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 10:00-19:00 and the project should be scheduled within this interval.

  17. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Kramer, Michael; Possenti, Andrea; Manchester, Dick; Lyne, Andrew; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Stairs, Ingrid; Faulkner, Andrew; Eatough, Ralph; Lorimer, Duncan Ross

    2008-04-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 10:00-19:00 and the project should be scheduled within this interval.

  18. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Kramer, Michael; Possenti, Andrea; Manchester, Dick; Lyne, Andrew; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Stairs, Ingrid; Faulkner, Andrew; Eatough, Ralph; Lorimer, Duncan Ross

    2007-10-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 10:00-19:00 and the project should be scheduled within this interval.

  19. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Kramer, Michael; Possenti, Andrea; Manchester, Dick; Lyne, Andrew; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Camilo, Fernando; Stairs, Ingrid; Faulkner, Andrew; Lorimer, Duncan Ross

    2006-10-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 10:00-19:00 and the project should be scheduled within this interval.

  20. Timing of binary and millisecond PKSMB/PH pulsars

    NASA Astrophysics Data System (ADS)

    Eatough, Ralph; Possenti, Andrea; Manchester, Dick; Kramer, Michael; Lyne, Andrew; Hobbs, George; McLaughlin, Maura; Burgay, Marta; D'Amico, Nichi; Stairs, Ingrid; Faulkner, Andrew; Lorimer, Duncan Ross

    2009-04-01

    This proposal concentrates the timing observations of binary and millisecond pulsars discovered by us in the Parkes Multibeam (PKSMB) and high-latitude (PH) surveys. In order to fully exploit the scientific promises of our discoveries it is essential to perform continued timing observations. It is crucial that the observing sessions be spaced at three-to-five week intervals. The pulsars will be visible during LST 10:00-19:00 and the project should be scheduled within this interval.

  1. Population Studies of Radio and Gamma-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K; Gonthier, Peter; Coltisor, Stefan

    2004-01-01

    Rotation-powered pulsars are one of the most promising candidates for at least some of the 40-50 EGRET unidentified gamma-ray sources that lie near the Galactic plane. Since the end of the EGRO mission, the more sensitive Parkes Multibeam radio survey has detected mere than two dozen new radio pulsars in or near unidentified EGRET sources, many of which are young and energetic. These results raise an important question about the nature of radio quiescence in gamma-ray pulsars: is the non-detection of radio emission a matter of beaming or of sensitivity? The answer is very dependent on the geometry of the radio and gamma-ray beams. We present results of a population synthesis of pulsars in the Galaxy, including for the first time the full geometry of the radio and gamma-ray beams. We use a recent empirically derived model of the radio emission and luminosity, and a gamma-ray emission geometry and luminosity derived theoretically from pair cascades in the polar slot gap. The simulation includes characteristics of eight radio surveys of the Princeton catalog plus the Parkes MB survey. Our results indicate that EGRET was capable of detecting several dozen pulsars as point sources, with the ratio of radio-loud to radio-quiet gamma-ray pulsars increasing significantly to about ten to one when the Parkes Survey is included. Polar cap models thus predict that many of the unidentified EGRET sources could be radio-loud gamma- ray pulsars, previously undetected as radio pulsars due to distance, large dispersion and lack of sensitivity. If true, this would make gamma-ray telescopes a potentially more sensitive tool for detecting distant young neutron stars in the Galactic plane.

  2. Is Jupiter's magnetosphere like a pulsar's or earth's?

    NASA Technical Reports Server (NTRS)

    Kennel, C. F.; Coroniti, F. V.

    1974-01-01

    The application of pulsar physics to determine the magnetic structure in the planet Jupiter outer magnetosphere is discussed. A variety of theoretical models are developed to illuminate broad areas of consistency and conflict between theory and experiment. Two possible models of Jupiter's magnetosphere, a pulsar-like radial outflow model and an earth-like convection model, are examined. A compilation of the simple order of magnitude estimates derivable from the various models is provided.

  3. PSR 1820-11 : A binary gamma-ray pulsar

    NASA Astrophysics Data System (ADS)

    Li, Ti-pei; Wu, Mei

    1990-09-01

    Significant pulsation structure in phase distribution in the 50-6000MeV gamma-rays from the direction of the binary radio pulsar PSR 1820-11 in the COS-B data was obtained using the folding algorithm. Besides the period search, a spatial analysis was Bade and a clear point-like gamma-ray image was found at the pulsar's position.

  4. Towards robust gravitational wave detection with pulsar timing arrays

    NASA Astrophysics Data System (ADS)

    Cornish, Neil J.; Sampson, Laura

    2016-05-01

    Precision timing of highly stable millisecond pulsars is a promising technique for the detection of very low frequency sources of gravitational waves. In any single pulsar, a stochastic gravitational wave signal appears as an additional source of timing noise that can be absorbed by the noise model, and so it is only by considering the coherent response across a network of pulsars that the signal can be distinguished from other sources of noise. In the limit where there are many gravitational wave sources in the sky, or many pulsars in the array, the signals produce a unique tensor correlation pattern that depends only on the angular separation between each pulsar pair. It is this distinct fingerprint that is used to search for gravitational waves using pulsar timing arrays. Here we consider how the prospects for detection are diminished when the statistical isotropy of the timing array or the gravitational wave signal is broken by having a finite number of pulsars and a finite number of sources. We find the standard tensor-correlation analysis to be remarkably robust, with a mild impact on detectability compared to the isotropic limit. Only when there are very few sources and very few pulsars does the standard analysis begin to fail. Having established that the tensor correlations are a robust signature for detection, we study the use of "sky scrambles" to break the correlations as a way to increase confidence in a detection. This approach is analogous to the use of "time slides" in the analysis of data from ground-based interferometric detectors.

  5. A millisecond pulsar in an extremely wide binary system

    NASA Astrophysics Data System (ADS)

    Bassa, C. G.; Janssen, G. H.; Stappers, B. W.; Tauris, T. M.; Wevers, T.; Jonker, P. G.; Lentati, L.; Verbiest, J. P. W.; Desvignes, G.; Graikou, E.; Guillemot, L.; Freire, P. C. C.; Lazarus, P.; Caballero, R. N.; Champion, D. J.; Cognard, I.; Jessner, A.; Jordan, C.; Karuppusamy, R.; Kramer, M.; Lazaridis, K.; Lee, K. J.; Liu, K.; Lyne, A. G.; McKee, J.; Osłowski, S.; Perrodin, D.; Sanidas, S.; Shaifullah, G.; Smits, R.; Theureau, G.; Tiburzi, C.; Zhu, W. W.

    2016-08-01

    We report on 22 yr of radio timing observations of the millisecond pulsar J1024-0719 by the telescopes participating in the European Pulsar Timing Array (EPTA). These observations reveal a significant second derivative of the pulsar spin frequency and confirm the discrepancy between the parallax and Shklovskii distances that has been reported earlier. We also present optical astrometry, photometry and spectroscopy of 2MASS J10243869-0719190. We find that it is a low-metallicity main-sequence star (K7V spectral type, [M/H] = -1.0, Teff = 4050 ± 50 K) and that its position, proper motion and distance are consistent with those of PSR J1024-0719. We conclude that PSR J1024-0719 and 2MASS J10243869-0719190 form a common proper motion pair and are gravitationally bound. The gravitational interaction between the main-sequence star and the pulsar accounts for the spin frequency derivatives, which in turn resolves the distance discrepancy. Our observations suggest that the pulsar and main-sequence star are in an extremely wide (Pb > 200 yr) orbit. Combining the radial velocity of the companion and proper motion of the pulsar, we find that the binary system has a high spatial velocity of 384 ± 45 km s-1 with respect to the local standard of rest and has a Galactic orbit consistent with halo objects. Since the observed main-sequence companion star cannot have recycled the pulsar to millisecond spin periods, an exotic formation scenario is required. We demonstrate that this extremely wide-orbit binary could have evolved from a triple system that underwent an asymmetric supernova explosion, though find that significant fine-tuning during the explosion is required. Finally, we discuss the implications of the long period orbit on the timing stability of PSR J1024-0719 in light of its inclusion in pulsar timing arrays.

  6. WIDE RADIO BEAMS FROM {gamma}-RAY PULSARS

    SciTech Connect

    Ravi, V.; Manchester, R. N.; Hobbs, G.

    2010-06-10

    We investigate the radio and {gamma}-ray beaming properties of normal and millisecond pulsars (MSPs) by selecting two samples from the known populations. The first, Sample G, contains pulsars which are detectable in blind searches of {gamma}-ray data from the Fermi Large Area Telescope. The second, Sample R, contains pulsars detectable in blind radio searches which have spin-down luminosities E>10{sup 34} erg s{sup -1}. We analyze the fraction of the {gamma}-ray-selected Sample G which have detectable radio pulses and the fraction of the radio-selected Sample R which have detectable {gamma}-ray pulses. Twenty of our 35 Sample G pulsars have already observed radio pulses. This rules out low-altitude polar-cap beaming models if, as is currently believed, {gamma}-ray beams are generated in the outer magnetosphere and are very wide. We further find that, for the highest-E pulsars, the radio and {gamma}-ray beams have comparable beaming factors, i.e., the beams cover similar regions of the sky as the star rotates. For lower-E {gamma}-ray emitting pulsars, the radio beams have about half of the {gamma}-ray sky coverage. These results suggest that, for high-E young and MSPs, the radio emission originates in wide beams from regions high in the pulsar magnetosphere, probably close to the null-charge surface and to the {gamma}-ray emitting regions. Furthermore, it suggests that for these high-E pulsars, as in the {gamma}-ray case, features in the radio profile represent caustics in the emission beam pattern.

  7. Magnetar-like Spectral Index Flattening of the High Magnetic Field Pulsar PSR J1119-6127

    NASA Astrophysics Data System (ADS)

    Pearlman, Aaron B.; Majid, Walid A.; Horiuchi, Shinji; Kocz, Jonathon; Lippuner, Jonas; Prince, Thomas A.

    2016-12-01

    -band, we find a spectral index of -0.52(6) in agreement with our initial result. The spectral index has flattened by a factor of approximately 4 compared to previous measurements by Majid et al. (2016; arXiv:1612.02868) across these frequency bands. We interpret this change as evidence of additional magnetar-like behavior from PSR J1119-6127, as these spectral index measurements are similar to those observed from other magnetars, such XTE J1810-197 (Camilo et al. (2007); Lazaridis et al. (2008)), SGR J1745-2900 (Torne et al. (2015)), and PSR J1622-4950 (Anderson et al. (2012)). We are continuing to monitor changes in the spectrum of PSR J1119-6127 at S-band and X-band, and we encourage further observations across multiple wavelengths. We thank the DSN and Canberra Deep Space Communication Complex (CDSCC) teams for scheduling these observations. *%K Radio, X-ray, Gamma Ray, Neutron Star, Transient, Pulsar, Magnetar

  8. ON THE POLAR CAP CASCADE PAIR MULTIPLICITY OF YOUNG PULSARS

    SciTech Connect

    Timokhin, A. N.; Harding, A. K.

    2015-09-10

    We study the efficiency of pair production in polar caps of young pulsars under a variety of conditions to estimate the maximum possible multiplicity of pair plasma in pulsar magnetospheres. We develop a semi-analytic model for calculation of cascade multiplicity which allows efficient exploration of the parameter space and corroborate it with direct numerical simulations. Pair creation processes are considered separately from particle acceleration in order to assess different factors affecting cascade efficiency, with acceleration of primary particles described by recent self-consistent non-stationary model of pair cascades. We argue that the most efficient cascades operate in the curvature radiation/synchrotron regime, the maximum multiplicity of pair plasma in pulsar magnetospheres is ∼few × 10{sup 5}. The multiplicity of pair plasma in magnetospheres of young energetic pulsars weakly depends on the strength of the magnetic field and the radius of curvature of magnetic field lines and has a stronger dependence on pulsar inclination angle. This result questions assumptions about very high pair plasma multiplicity in theories of pulsar wind nebulae.

  9. STRONG FIELD EFFECTS ON PULSAR ARRIVAL TIMES: GENERAL ORIENTATIONS

    SciTech Connect

    Wang Yan; Creighton, Teviet; Price, Richard H.; Jenet, Frederick A.

    2009-11-10

    A pulsar beam passing close to a black hole can provide a probe of very strong gravitational fields even if the pulsar itself is not in a strong field region. In the case that the spin of the hole can be ignored, we have previously shown that all strong field effects on the beam can be understood in terms of two 'universal' functions: F(phi{sub in}) and T(phi{sub in}) of the angle of beam emission phi{sub in}; these functions are universal in that they depend only on a single parameter, the pulsar/black hole distance from which the beam is emitted. Here we apply this formalism to general pulsar-hole-observer geometries, with arbitrary alignment of the pulsar spin axis and arbitrary pulsar beam direction and angular width. We show that the analysis of the observational problem has two distinct elements: (1) the computation of the location and trajectory of an observer-dependent 'keyhole' direction of emission in which a signal can be received by the observer; and (2) the determination of an annulus that represents the set of directions containing beam energy. Examples of each are given along with an example of a specific observational scenario.

  10. XMM-Newton Observations of Four Millisecond Pulsars

    NASA Technical Reports Server (NTRS)

    Zavlin, Vyacheslav E.

    2005-01-01

    I present an analysis of the XMM-Newton observations of four millisecond pulsars, J0437-4715, J2124-3358, J1024-0719, and J0034-0534. The new data provide strong evidence of thermal emission in the X-ray flux detected from the first three objects. This thermal component is best interpreted as radiation from pulsar polar caps covered with a nonmagnetic hydrogen atmosphere. A nonthermal power-law component, dominating at energies E greater than or equal to 3 keV, can also be present in the detected X-ray emission. For PSR J0437-4715, the timing analysis reveals that the shape and pulsed fraction of the pulsar light curves are energy dependent. This, together with the results obtained from the phase-resolved spectroscopy, supports the two-component (thermal plus nonthermal) interpretation of the pulsar's X-ray radiation. Highly significant pulsations have been found in the X-ray flux of PSRs 52124-3358 and 51024-0719. For PSR 50034-0534, a possible X-ray counterpart of the radio pulsar has been suggested. The inferred properties of the detected thermal emission are compared with predictions of radio pulsar models.

  11. High-energy flux evolution of Pulsar Wind Nebulae

    SciTech Connect

    Mattana, F.; Falanga, M.; Goetz, D.

    2008-12-24

    The very high energy {gamma}-ray spectra of Pulsar Wind Nebulae are interpreted as due to inverse Compton scattering of ultrarelativistic electrons on the ambient photons, whereas their X-ray spectra are due to synchrotron emission. We investigate the relation between the {gamma}- and X-ray emission and the pulsars' spin-down luminosity and characteristic age. We find that the {gamma}-to X-ray flux ratio of the nebulae is inversely proportional to the spin-down luminosity ({proportional_to}E{sup -1.9}) and to the characteristic age ({proportional_to}{tau}{sub c}{sup 2.2}) of the parent pulsar. We interpret these results as due to the evolution of the electron energy distribution and the nebular dynamics, supporting the idea of so-called relic pulsar wind nebulae. These empirical relations provide a new tool to classify unidentified diffuse {gamma}-ray sources and to estimate the spin-down luminosity and characteristic age for four rotation powered pulsars with no detected pulsation from the X- and {gamma}--ray properties of the associated pulsar wind nebulae.

  12. X-Ray States of Redback Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Linares, M.

    2014-11-01

    Compact binary millisecond pulsars with main-sequence donors, often referred to as "redbacks," constitute the long-sought link between low-mass X-ray binaries and millisecond radio pulsars and offer a unique probe of the interaction between pulsar winds and accretion flows. We present a systematic study of eight nearby redbacks, using more than 100 observations obtained with Swift's X-ray Telescope. We distinguish between three main states: pulsar, disk, and outburst states. We find X-ray mode switching in the disk state of PSR J1023+0038 and XSS J12270-4859, similar to what was found in the other redback that showed evidence for accretion: rapid, recurrent changes in X-ray luminosity (0.5-10 keV, L X), between (6-9) × 1032 erg s-1 (disk-passive state) and (3-5) × 1033 erg s-1 (disk-active state). This strongly suggests that mode switching—which has not been observed in quiescent low-mass X-ray binaries—is universal among redback millisecond pulsars in the disk state. We briefly explore the implications for accretion disk truncation and find that the inferred magnetospheric radius in the disk state of PSR J1023+0038 and XSS J12270-4859 lies outside the light cylinder. Finally, we note that all three redbacks that have developed accretion disks have relatively high L X in the pulsar state (>1032 erg s-1).

  13. Black Widow Pulsar radiation hydrodynamics simulation using Castro: Methodology

    NASA Astrophysics Data System (ADS)

    Barrios Sazo, Maria; Zingale, Michael; Zhang, Weiqun

    2017-01-01

    A black widow pulsar (BWP) is a millisecond pulsar in a tight binary system with a low mass star. The fast rotating pulsar emits intense radiation, which injects energy and ablates the companion star. Observation of the ablation is seen as pulsar eclipses caused by a larger object than the companion star Roche lobe. This phenomenon is attributed to a cloud surrounding the evaporating star. We will present the methodology for modeling the interaction between the radiation coming from the pulsar and the companion star using the radiation hydrodynamics code Castro. Castro is an adaptive mesh refinement (AMR) code that solves the compressible hydrodynamic equations for astrophysical flows with simultaneous refinement in space and time. The code also includes self-gravity, nuclear reactions and radiation. We are employing the gray-radiation solver, which uses a mixed-frame formulation of radiation hydrodynamics under the flux-limited diffusion approximation. In our setup, we are modeling the companion star with the radiation field as a boundary condition, coming from one side of the domain. In addition to a model setup in 2-d axisymmetry, we also have a 3-d setup, which is more physical given the nature of the system considering the companion is facing the pulsar on one side. We discuss the progress of our calculations, first results, and future work.The work at Stony Brook was supported by DOE/Office of Nuclear Physics grant DE-FG02-87ER40317

  14. ON THE GLOBAL STRUCTURE OF PULSAR FORCE-FREE MAGNETOSPHERE

    SciTech Connect

    Petrova, S. A.

    2013-02-20

    The dipolar magnetic field structure of a neutron star is modified by the plasma originating in the pulsar magnetosphere. In the simplest case of a stationary axisymmetric force-free magnetosphere, a self-consistent description of the fields and currents is given by the well-known pulsar equation. Here we revise the commonly used boundary conditions of the problem in order to incorporate the plasma-producing gaps and to provide a framework for a truly self-consistent treatment of the pulsar magnetosphere. A generalized multipolar solution of the pulsar equation is found, which, as compared to the customary split monopole solution, is suggested to better represent the character of the dipolar force-free field at large distances. In particular, the outer gap location entirely inside the light cylinder implies that beyond the light cylinder the null and critical lines should be aligned and become parallel to the equator at a certain altitude. Our scheme of the pulsar force-free magnetosphere, which will hopefully be followed by extensive analytic and numerical studies, may have numerous implications for different fields of pulsar research.

  15. Be/X-Ray Pulsar Binary Science with LOFT

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2011-01-01

    Accretion disks are ubiquitous in astronomical sources. Accretion powered pulsars are a good test bed for accretion disk physics, because unlike for other objects, the spin of the neutron star is directly observable allowing us to see the effects of angular momentum transfer onto the pulsar. The combination of a sensitive wide-field monitor and the large area detector on LOFT will enable new detailed studies of accretion powered pulsars which I will review. RXTE observations have shown an unusually high number of Be/X-ray pulsar binaries in the SMC. Unlike binaries in the Milky Way, these systems are all at the same distance, allowing detailed population studies using the sensitive LOFT WFM, potentially providing connections to star formation episodes. For Galactic accreting pulsar systems, LOFT will allow measurement of spectral variations within individual pulses, mapping the accretion column in detail for the first time. LOFT will also provide better constraints on magnetic fields in accreting pulsars, allowing measurements of cyclotron features, observations of transitions into the centrifugal inhibition regime, and monitoring of spin-up rate vs flux correlations. Coordinated multi-wavelength observations are crucial to extracting the best science from LOFT from these and numerous other objects.

  16. Origin and radio pulse properties of millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Chen, Kaiyou; Ruderman, Malvin

    1993-05-01

    Millisecond pulsars may be formed by the accretion induced collapse of massive white dwarfs or from neutron stars spun-up by accretion from low-mass companions. Because the solid crust of a neutron star is expected to be moved by strong stresses which build up during spin-up or spin-down, the expected surface magnetic field structures are quite different for millisecond pulsars formed in these two different scenarios. During prolonged spin-up the moving crust compresses all stellar surface magnetic field into a small region around the spin axis. This can account for observed properties of disk population millisecond pulsars and their radio pulses, especially those of the most rapidly spinning ones such as PSR 1937 + 21 (two pulse components of comparable intensity 180 deg apart; extremely narrow component widths; fan beam emission so that almost all such millisecond pulsars are observable despite the narrow widths; nearly 100 percent linear polarization and fixed polarization angle at radio frequencies below one GHz for one of the two pulse components). Radio pulse properties of typical millisecond pulsars in globular clusters appear to be different from those of the disk population, and may indicate a different genesis, e.g., accretion induced collapse, for most of these pulsars.

  17. Single Pulse Searches for Pulsars in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Cushey, Daniel Joseph; Majid, Walid A.; Prince, Thomas Allen

    2017-01-01

    The discovery of the magnetar J1745-2900 within 3'' of Sgr A* by Mori et al. (2013) has renewed strong interest in Galactic Center (GC) pulsars and motivated expanded searches for their pulses due to their extensive applications to gravitational and plasma physics. There are currently 5 known pulsars within 15' of the Sgr A*; however, gamma ray excesses from the GC suggest a source population of 102-103 millisecond pulsars within the same region. Although this discrepancy is readily explained by the hyper-strong scattering environment of the GC which obscures pulses, the discovery of J1745-2900 challenges this attribution and further observations and analysis are needed to reconcile the observed GC pulsar population with theory. We present a pipeline developed to search for these "missing" GC pulsars using a single pulse search algorithm. Observations of the GC using the Deep Space Network 70m antenna were taken in the high frequency regime in order to minimize scattering, and search parameters were calibrated using pulses from RRAT J1819-1458. Any detected pulses that are distinct from those of J1745-2900 warrant extensive follow-up observations and analysis, and confirmed new members of the elusive GC pulsar population would be incredibly valuable as probes of the GC's magnetic and potential fields.

  18. Exploring the Physical Conditions in Millisecond Pulsar Emission Regions

    NASA Astrophysics Data System (ADS)

    Rankin, Joanna 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 Pulsar 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 despite having radically different magnetospheric sizes and magnetic field strengths. MSPs thus provide an extreme context for studying pulsar radio emission. Particle currents along the magnetic polar fluxtube 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 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.

  19. Preferred Frame Effects in Relativistic Binary Pulsars

    NASA Astrophysics Data System (ADS)

    Kramer, M.; Wex, N.

    2008-03-01

    We summarize our recently presented consistent, theory-independent methodology to measure preferred-frame effects (PFEs) in binary pulsars that exhibit a high rate of periastron advance. In these systems the existence of a preferred frame for gravity leads to an observable characteristic signature in the timing data. A newly developed PFE timing model can be used to either measure or constrain the parameters related to a violation of the local Lorentz invariance of gravity in the strong internal fields of neutron stars. In particular, in the presence of PFEs we expect a set of the new timing parameters to have a unique relationship that can be measured and tested incontrovertibly. A combination of several suitable systems in a PFE antenna array provides full sensitivity to possible violations of local Lorentz invariance in strong gravitational fields in all directions of the sky.

  20. The Optical Spectrum of the Geminga Pulsar

    NASA Technical Reports Server (NTRS)

    Martin, Christopher; Halpern, Jules P.; Schiminovich, David; Oliversen, Ronald (Technical Monitor)

    2001-01-01

    We obtained an optical spectrum of the isolated pulsar Geminga at the Keck Observatory. The optical object is at the limit of spectroscopic capability of any telescope, with a continuum flux that is approx. 0.5% of the dark sky on Mauna Kea. With particular attention paid to the dominant systematics of sky subtraction in our observing and analysis methods, we attained approx. 0.1% systematics in heavily binned spectra. The resulting spectrum spanning 3700 - 8000 A has a flat power-law shape f(sub nu) proportional to nu(exp -0.8) and a broad dip over 6300 - 6500 A. Thermal radiation cannot explain the optical spectrum of Geminga. The dominant component can be modeled as either electron synchrotron emission and ion (proton) cyclotron absorption, or ion cyclotron emission, the latter in a 10(exp 11) G magnetic field.

  1. Accreting Millisecond Pulsars and Fundamental Physics

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2005-01-01

    X-ray emission from the surfaces of rapidly rotating neutron stars encodes information about their global properties as well as physical conditions locally. Detailed modelling of, for example, the energy dependent pulse profiles observed from accreting millisecond pulsars and thermonuclear burst oscillations can be used to derive constraints on the masses and radii of neutron stars. These measurements provide direct information on the properties of the dense matter equation of state of the supranuclear density matter in their interiors. Study of absorption lines created in the surface layers can also provide measurements of masses and radii, and may be able to probe aspects of relativistic gravity, such as frame dragging. I will discuss the results of recent efforts to carry out such measurements and their implications for the properties of dense matter.

  2. SN 1054: A pulsar-powered supernova?

    NASA Astrophysics Data System (ADS)

    Li, Shao-Ze; Yu, Yun-Wei; Huang, Yan

    2015-11-01

    The famous ancient supernova SN 1054 could have been too bright to be explained in the “standard” radioactive-powered supernova scenario. As an alternative attempt, we demonstrate that the spin-down of the newly born Crab pulsar could provide a sufficient energy supply to make SN 1054 visible at daytime for 23 days and at night for 653 days, where a one-zone semi-analytical model is employed. Our results indicate that SN 1054 could be a “normal” cousin of magnetar-powered superluminous supernovae. Therefore, SN 1054-like supernovae could be a probe to uncover the properties of newly born neutron stars, which provide initial conditions for studies on neutron star evolutions.

  3. Rotational evolution of the Crab pulsar in the wind braking model

    NASA Astrophysics Data System (ADS)

    Kou, F. F.; Tong, H.

    2015-06-01

    The pulsar wind model is updated by considering the effect of particle density and pulsar death. It can describe both the short-term and long-term rotational evolution of pulsars consistently. It is applied to model the rotational evolution of the Crab pulsar. The pulsar is spun down by a combination of magnetic dipole radiation and particle wind. The parameters of the Crab pulsar, including magnetic field, inclination angle, and particle density are calculated. The primary particle density in acceleration region is about 103 times the Goldreich-Julian charge density. The lower braking index between glitches is due to a larger outflowing particle density. This may be glitch induced magnetospheric activities in normal pulsars. Evolution of braking index and the Crab pulsar in P-dot{P} diagram are calculated. The Crab pulsar will evolve from magnetic dipole radiation dominated case towards particle wind-dominated case. Considering the effect of pulsar `death', the Crab pulsar (and other normal pulsars) will not evolve to the cluster of magnetars but downwards to the death valley. Different acceleration models are also considered. Applications to other sources are also discussed, including pulsars with braking index measured, and the magnetar population.

  4. Population statistics of radio and γ-ray pulsars from the Galactic disk

    NASA Astrophysics Data System (ADS)

    Gonthier, Peter L.; Story, Sarah A.; Clow, Brian D.; Harding, Alice K.

    2008-01-01

    We present results of our population synthesis of normal and millisecond pulsars from the Galactic disk. Over the past several years, a program has been developed to simulate pulsar birth, evolution, and emission using Monte Carlo techniques. We have added to the program the capability to simulate millisecond pulsars, which are old, recycled pulsars with extremely short periods. We model the spatial distribution of millisecond pulsars by assuming they start with a random kick velocity and then evolve through the Galactic potential. We use a polar cap/slot gap model for gamma-ray emission from both millisecond and normal pulsars. We also include gamma-ray emission from an outer-gap model to compare the statistics of radio-loud and radio-faint gamma-ray pulsars on the same footing as pulsars from our polar cap/slot gap model. From our studies of radio pulsars that have clearly identifiable core and cone components, in which we fit the polarization sweep as well as the pulse profiles to constrain the viewing geometry, we develop a model describing the ratio of radio core-to-cone peak fluxes. In this model, short period pulsars are more cone-dominated than in our previous studies. We present the preliminary results of our recent study including comparisons between these two groups of pulsars and the implications for observing these pulsars with GLAST and AGILE. GLAST should detect significant numbers of millisecond pulsars.

  5. Gamma-ray connection of Pulsars-Pulsar Wind Nebulae: From GeV to TeV energies

    NASA Astrophysics Data System (ADS)

    López-Coto, Rubén; de Ona Wilhelmi, Emma

    2015-08-01

    Pulsars are the remnants of massive star explosions and Pulsar Wind Nebulae (PWNe) are the bubbles of relativistic particles and magnetic field surrounding pulsars. The acceleration in PWNe is produced when the pulsar's relativistic wind interacts with its surrounding medium and particles are accelerated at the shock region. The non-thermal photon emission ranges from the radio to the very-high-energy (VHE) range and it is believed to be originated in synchrotron, curvature and inverse Compton processes.So far, pulsars and PWNe represent the largest population of identified GeV and TeV sources. In this contribution, we will describe the recent measurements on young PWNe such as the Crab whose inverse Compton peak was recently accurately determined. We will also discuss the origin of the GeV gamma-ray flares and their non-detection at any other wavelength, together with the recent reports of pulsed emission up to TeV energies. This result evidences the extreme acceleration of electrons in the surrounding of the Crab pulsar, up to Lorenz factors of 5 × 106. We will also put in context the recent discovery of VHE pulsed emission from the Vela pulsar. We will discuss the case of the inefficient pulsar at the center of 3C 58, a PWN discovered by Fermi at GeV energies and by MAGIC at TeV. In addition, we will also present population studies comparing several properties of the central engine such as age or spin-down power with the gamma-ray luminosity of their surrounding PWNe. We will finally show the measurement prospects for this kind of sources with the future Cherenkov Telescope Array.

  6. Youngest Radio Pulsar Revealed with Green Bank Telescope

    NASA Astrophysics Data System (ADS)

    2002-04-01

    Astronomers using the National Science Foundation's (NSF) newly commissioned Robert C. Byrd Green Bank Telescope (GBT) have detected remarkably faint radio signals from an 820 year-old pulsar, making it the youngest radio-emitting pulsar known. This discovery pushes the boundaries of radio telescope sensitivity for discovering pulsars, and will enable scientists to conduct observations that could lead to a better understanding of how these stars evolve. The Robert C. Byrd Green Bank Telescope Robert C. Byrd Green Bank Telescope "Important questions about pulsars may be answered by long-term monitoring of objects such as the one we just detected," said Fernando Camilo of Columbia University in New York City. "Young pulsars are particularly rare, and being able to study such a young one at radio wavelengths provides an outstanding opportunity to learn critical facts about their evolution and workings." The results of this research, based on observations conducted on February 22-23, 2002, were accepted for publication in the Astrophysical Journal Letters. Scientists have long suspected that a pulsar - a rapidly spinning, superdense neutron star - was born when a giant star ended its life in a cataclysmic supernova explosion observed in late summer of 1181, as suggested by Japanese and Chinese historical records. For the past 20 years, astronomers have searched this supernova remnant (3C58), located 10,000 light-years away in the constellation Cassiopeia, for the telltale pulsations of a newly born pulsar. Late in 2001, data from NASA's Chandra X-ray satellite confirmed its existence, but it remained an elusive quarry for radio telescopes. "We believed from historical records and certainly knew from recent X-ray observations that this star was there," Camilo remarked, "but despite many attempts, no one had been able to find any radio pulsations from it because the signals are, it turns out, incredibly weak." For comparison, this pulsar's radio emission is some 250

  7. Pulsar Bursts Coming From Beachball-Sized Structures

    NASA Astrophysics Data System (ADS)

    2003-03-01

    In a major breakthrough for understanding what one of them calls "the most exotic environment in the Universe," a team of astronomers has discovered that powerful radio bursts in pulsars are generated by structures as small as a beach ball. VLA Image of Crab Nebula VLA Image of Crab Nebula (Click on Image for Larger Version) Pulsar Diagram Diagram of a Pulsar (Click on Image for Larger Version) "These are by far the smallest objects ever detected outside our solar system," said Tim Hankins, leader of the research team, which studied the pulsar at the center of the Crab Nebula, more than 6,000 light-years from Earth. "The small size of these regions is inconsistent with all but one proposed theory for how the radio emission is generated," he added. The other members of the team are Jeff Kern, James Weatherall and Jean Eilek. Hankins was a visiting scientist at Arecibo Observatory in Puerto Rico at the time the pulsar observations were made. He and Eilek are professors at the New Mexico Institute of Mining and Technology (New Mexico Tech) in Socorro, NM. Kern is a graduate student at NM Tech and a predoctoral fellow at the National Radio Astronomy Observatory (NRAO) in Socorro. Weatherall is an adjunct professor at NM Tech, currently working at the Federal Aviation Administration. The astronomers reported their discovery in the March 13 edition of the scientific journal Nature. Pulsars are superdense neutron stars, the remnants of massive stars that exploded as supernovae. Pulsars emit powerful beams of radio waves and light. As the neutron star spins, the beam sweeps through space like the beam of a lighthouse. When such a beam sweeps across the Earth, astronomers see a pulse from the pulsar. The Crab pulsar spins some 33 times every second. British radio astronomers discovered pulsars in 1967, one receiving the Nobel Prize for the discovery. In the years since, the method by which pulsars produce their powerful beams of electromagnetic radiation has remained a

  8. Probing the origin of Pulsar wind with a Black widow pulsar 2FGL J2339.6-0532

    NASA Astrophysics Data System (ADS)

    Yatsu, Yoichi; Shibata, Shinpei; Kawai, Nobuyuki; Kataoka, Jun; Saito, Yoshihiko

    Multi-wavelength observations of a black widow binary system 2FGL2339.6-0532 are presented. Black widow pulsars are believed to be in the intermediate stage between LMXB and isolated millisecond pulsars(MSPs). In a typical black widow system, the recycled MSP is evaporating up its companion star by the powerful pulsar wind. Fermi gamma-ray source 2FGL2339.6-0532 is recently categorized as an black widow pulsar. It possesses a K-star companion orbiting at a period of 4.63 h that corresponds to an orbit radius of about 10(11) cm for a standard NS mass. Our optical observations utilizing OISTER show clear sinusoidal light curves at various wavelength covering Ks B band. Phase resolved SED precisely constrained the size of the companion star and temperature. X-ray spectra taken with Suzaku revealed steady soft X-ray excess below 1 keV energy range that may be originated in blackbody emission from the neutron surface. While In hard X-ray energy band the X-ray light curve shows double peak modulation synchronized with the orbital motion indicating that the hard X-ray may be from the surface of the companion star. To explain the hard X-ray behavior we examined a simple geometry and estimated the physical state of the pulsar wind at immediate vicinity of the light cylinder of the pulsar.

  9. TOWARD AN EMPIRICAL THEORY OF PULSAR EMISSION. XI. UNDERSTANDING THE ORIENTATIONS OF PULSAR RADIATION AND SUPERNOVA “KICKS”

    SciTech Connect

    Rankin, Joanna M.

    2015-05-10

    Two entwined problems have remained unresolved since pulsars were discovered nearly 50 yr ago: the orientation of their polarized emission relative to the emitting magnetic field and the direction of putative supernova “kicks” relative to their rotation axes. The rotational orientation of most pulsars can be inferred only from the (“fiducial”) polarization angle of their radiation, when their beam points directly at the Earth and the emitting polar fluxtube field is ∥ to the rotation axis. Earlier studies have been unrevealing owing to the admixture of different types of radiation (core and conal, two polarization modes), producing both ∥ or ⊥ alignments. In this paper we analyze some 50 pulsars having three characteristics: core radiation beams, reliable absolute polarimetry, and accurate proper motions (PMs). The “fiducial” polarization angle of the core emission, we then find, is usually oriented ⊥ to the PM direction on the sky. The primary core emission is polarized ⊥ to the projected magnetic field in Vela and other pulsars where X-ray imaging reveals the orientation. This shows that the PMs usually lie ∥ to the rotation axes on the sky. Two key physical consequences then follow: first, to the extent that supernova “kicks” are responsible for pulsar PMs, they are mostly ∥ to the rotation axis; and, second, most pulsar radiation is heavily processed by the magnetospheric plasma such that the lowest altitude “parent” core emission is polarized ⊥ to the emitting field, propagating as the extraordinary (X) mode.

  10. Optical properties of Ge xSb 20- xTe 80 thin films and their changes by light illumination

    NASA Astrophysics Data System (ADS)

    Pamukchieva, V.; Szekeres, A.

    2008-03-01

    The influence of light illumination on the optical constants of chalcogenide thin films with non-stoichiometric Ge xSb 20- xTe 80 ( x = 15, 17, 19) composition is studied by spectral ellipsometry in the visible range of light. The films were deposited onto glass substrates by vacuum thermal evaporation of parent glasses and were subjected to an 1-h illumination with a 500 W HBO mercury lamp. It has been established that illumination of the films leads to a decrease of the refractive index, n, in the whole spectral region studied and to an increase of the extinction coefficient, k, in the range of 600-800 nm. The optical bandgap energy Eg values are within 0.55-0.76 eV with a tendency to increase with increasing the Ge content. Illumination resulted in a sharp decrease of the Eg values indicating structural change in the films. Leaving the films at atmospheric conditions the optical parameters values change toward their initial values of unilluminated state.

  11. Multiwavelength Observations of the Black Hole Transient XTE J1752-223 during Its 2010 Outburst Decay

    NASA Astrophysics Data System (ADS)

    Chun, Y. Y.; Dinçer, T.; Kalemci, E.; Güver, T.; Tomsick, J. A.; Buxton, M. M.; Brocksopp, C.; Corbel, S.; Cabrera-Lavers, A.

    2013-06-01

    Galactic black hole transients show many interesting phenomena during outburst decays. We present simultaneous X-ray (RXTE, Swift, and INTEGRAL), and optical/near-infrared (O/NIR) observations (SMARTS) of the X-ray transient XTE J1752-223 during its outburst decay in 2010. The multiwavelength observations over 150 days in 2010 cover the transition from soft to hard spectral state. We discuss the evolution of radio emission with respect to the O/NIR light curve which shows several flares. One of those flares is bright and long, starting about 60 days after the transition in X-ray timing properties. During this flare, the radio spectral index becomes harder. Other smaller flares occur along with the X-ray timing transition, and also right after the detection of the radio core. We discuss the significances of these flares. Furthermore, using the simultaneous broadband X-ray spectra including INTEGRAL, we find that a high energy cut-off with a folding energy near 250 keV is necessary around the time that the compact jet is forming. The broadband spectrum can be fitted equally well with a Comptonization model. In addition, using photoelectric absorption edges in the XMM-Newton Reflection Grating Spectrometer X-ray spectra and the extinction of red clump giants in the direction of the source, we find a lower limit on the distance of >5 kpc.

  12. A decelerating jet observed by the EVN and VLBA in the X-ray transient XTE J1752-223

    NASA Astrophysics Data System (ADS)

    Yang, J.; Brocksopp, C.; Corbel, S.; Paragi, Z.; Tzioumis, T.; Fender, R. P.

    2010-11-01

    The recently discovered Galactic X-ray transient XTE J1752-223 entered its first known outburst in 2010, emitting from the X-ray to the radio regimes. Its general X-ray properties were consistent with those of a black hole candidate in various spectral states, when ejection of jet components is expected. To verify this, we carried out very long baseline interferometry (VLBI) observations. The measurements were carried out with the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA) at four epochs in 2010 February. The images at the first three epochs show a moving jet component that is significantly decelerated by the last epoch, when a new jet component appears that is likely to be associated with the receding jet side. The overall picture is consistent with an initially mildly relativistic jet, interacting with the interstellar medium or with swept-up material along the jet. The brightening of the receding ejecta at the final epoch can be well explained by initial Doppler deboosting of the emission in the decelerating jet.

  13. NuSTAR AND SWIFT OBSERVATIONS OF THE BLACK HOLE CANDIDATE XTE J1908+094 DURING ITS 2013 OUTBURST

    SciTech Connect

    Tao, Lian; Walton, Dominic J.; Fürst, Felix; Grefenstette, Brian W.; Harrison, Fiona A.; Tendulkar, Shriharsh P.; Tomsick, John A.; Boggs, Steven E.; Craig, William W.; Kennea, Jamie; Miller, Jon M.; Christensen, Finn E.; Gandhi, Poshak; Hailey, Charles J.; Krimm, Hans A.; Pottschmidt, Katja; Zhang, William W.; Stern, Daniel

    2015-09-20

    The black hole (BH) candidate XTE J1908+094 went into outburst for the first time since 2003 in 2013 October. We report on an observation with the Nuclear Spectroscopic Telescope Array (NuSTAR) and monitoring observations with Swift during the outburst. NuSTAR caught the source in the soft state: the spectra show a broad relativistic iron line, and the light curves reveal a ∼40 ks flare, with the count rate peaking about 40% above the non-flare level and with significant spectral variation. A model combining a multi-temperature thermal component, a power law, and a reflection component with an iron line provides a good description of the NuSTAR spectrum. Although relativistic broadening of the iron line is observed, it is not possible to constrain the BH spin with these data. The variability of the power-law component, which can also be modeled as a Comptonization component, is responsible for the flux and spectral change during the flare, suggesting that changes in the corona (or possibly continued jet activity) are the likely cause of the flare.

  14. An optical study of vacuum evaporated Se 85-xTe 15Bi x chalcogenide thin films

    NASA Astrophysics Data System (ADS)

    Ambika; Barman, P. B.

    2010-02-01

    Thin films of Se 85-xTe 15Bi x ( x=0, 1, 2, 3, 4, 5) glassy alloys prepared by melt quenching technique, are deposited on glass substrate using thermal evaporation technique under vacuum. The analysis of transmission spectra, measured at normal incidence, in the spectral range 400-1500 nm helphelps us in the optical characterization of thin films under study. Well -known Swanepoel's method is employed to determine the refractive index ( n) and film thickness ( d). The increase in n with increasing Bi content over the entire spectral range is related to the increased polarizability of the larger Bi atom (atomic radius 1.46 Å) compared with the Se atom (atomic radius 1.16 Å). Dispersion energy ( E d), average energy gap ( E0) and static refractive index ( n0) isare calculated using Wemple-DiDomenico model (WDD). The value of absorption coefficient ( α) and hence extinction coefficient ( k) hashave been determined from transmission spectra. Optical band gap ( E g) is estimated using Tauc's extrapolation and is found to decrease from 1.46 to 1.24 eV with the Bi addition. This behavior of optical band gap is interpreted in terms of electronegativity difference of the atoms involved and cohesive energy of the system.

  15. MULTIWAVELENGTH OBSERVATIONS OF THE BLACK HOLE TRANSIENT XTE J1752-223 DURING ITS 2010 OUTBURST DECAY

    SciTech Connect

    Chun, Y. Y.; Dincer, T.; Kalemci, E.; Guever, T.; Tomsick, J. A.; Buxton, M. M.; Brocksopp, C.; Corbel, S.; Cabrera-Lavers, A.

    2013-06-10

    Galactic black hole transients show many interesting phenomena during outburst decays. We present simultaneous X-ray (RXTE, Swift, and INTEGRAL), and optical/near-infrared (O/NIR) observations (SMARTS) of the X-ray transient XTE J1752-223 during its outburst decay in 2010. The multiwavelength observations over 150 days in 2010 cover the transition from soft to hard spectral state. We discuss the evolution of radio emission with respect to the O/NIR light curve which shows several flares. One of those flares is bright and long, starting about 60 days after the transition in X-ray timing properties. During this flare, the radio spectral index becomes harder. Other smaller flares occur along with the X-ray timing transition, and also right after the detection of the radio core. We discuss the significances of these flares. Furthermore, using the simultaneous broadband X-ray spectra including INTEGRAL, we find that a high energy cut-off with a folding energy near 250 keV is necessary around the time that the compact jet is forming. The broadband spectrum can be fitted equally well with a Comptonization model. In addition, using photoelectric absorption edges in the XMM-Newton Reflection Grating Spectrometer X-ray spectra and the extinction of red clump giants in the direction of the source, we find a lower limit on the distance of >5 kpc.

  16. Tugboat model for OB binaries, X-ray stars and pulsars.

    PubMed

    Helfand, D J; Tademaru, E

    1977-05-12

    An examination of the kinematical properties of binary OB stars, binary X-ray sources and pulsars suggests an evolutionary sequence linking an apparent low-velocity class of pulsars to the binary nature of their extreme Population I progenitors.

  17. TIMING AND INTERSTELLAR SCATTERING OF 35 DISTANT PULSARS DISCOVERED IN THE PALFA SURVEY

    SciTech Connect

    Nice, D. J.; Altiere, E.; Farrington, D.; Popa, L.; Wang, Y.; Bogdanov, S.; Camilo, F.; Cordes, J. M.; Brazier, A.; Chatterjee, S.; Hessels, J. W. T.; Kaspi, V. M.; Lyne, A. G.; Stappers, B. W.; Ransom, S. M.; Sanpa-arsa, S.; Allen, B.; Bhat, N. D. R.; Champion, D. J.; Crawford, F.; and others

    2013-07-20

    We have made extensive observations of 35 distant slow (non-recycled) pulsars discovered in the ongoing Arecibo PALFA pulsar survey. Timing observations of these pulsars over several years at Arecibo Observatory and Jodrell Bank Observatory have yielded high-precision positions and measurements of rotation properties. Despite being a relatively distant population, these pulsars have properties that mirror those of the previously known pulsar population. Many of the sources exhibit timing noise, and one underwent a small glitch. We have used multifrequency data to measure the interstellar scattering properties of these pulsars. We find scattering to be higher than predicted along some lines of sight, particularly in the Cygnus region. Finally, we present XMM-Newton and Chandra observations of the youngest and most energetic of the pulsars, J1856+0245, which has previously been associated with the GeV-TeV pulsar wind nebula HESS J1857+026.

  18. X-Ray Observations of High-B Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Olausen, S. A.; Zhu, W. W.; Vogel, J. K.; Kaspi, V. M.; Lyne, A. G.; Espinoza, C. M.; Stappers, B. W.; Manchester, R. N.; McLaughlin, M. A.

    2013-02-01

    The study of high-magnetic-field pulsars is important for examining the relationships between radio pulsars, magnetars, and X-ray-isolated neutron stars (XINSs). Here, we report on X-ray observations of three such high-magnetic-field radio pulsars. We first present the results of a deep XMM-Newton observation of PSR J1734-3333, taken to follow up on its initial detection in 2009. The pulsar's spectrum is well fit by a blackbody with a temperature of 300 ± 60 eV, with bolometric luminosity L_{{bb}}=2.0_{-0.7}^{+2.2}× 10^{32} {erg s^{-1}}≈ 0.0036 \\dot{E} for a distance of 6.1 kpc. We detect no X-ray pulsations from the source, setting a 1σ upper limit on the pulsed fraction of 60% in the 0.5-3 keV band. We compare PSR J1734-3333 to other rotation-powered pulsars of similar age and find that it is significantly hotter, supporting the hypothesis that the magnetic field affects the observed thermal properties of pulsars. We also report on XMM-Newton and Chandra observations of PSRs B1845-19 and J1001-5939. We do not detect either pulsar, setting 3σ upper limits on their blackbody temperatures of 48 and 56 eV, respectively. Despite the similarities in rotational properties, these sources are significantly cooler than all but one of the XINSs, which we attribute to the two groups having been born with different magnetic fields and hence evolving differently.

  19. X-RAY OBSERVATIONS OF HIGH-B RADIO PULSARS

    SciTech Connect

    Olausen, S. A.; Kaspi, V. M.; Zhu, W. W.; Vogel, J. K.; Lyne, A. G.; Espinoza, C. M.; Stappers, B. W.; Manchester, R. N.; McLaughlin, M. A.

    2013-02-10

    The study of high-magnetic-field pulsars is important for examining the relationships between radio pulsars, magnetars, and X-ray-isolated neutron stars (XINSs). Here, we report on X-ray observations of three such high-magnetic-field radio pulsars. We first present the results of a deep XMM-Newton observation of PSR J1734-3333, taken to follow up on its initial detection in 2009. The pulsar's spectrum is well fit by a blackbody with a temperature of 300 {+-} 60 eV, with bolometric luminosity L{sub bb}=2.0{sub -0.7}{sup +2.2} Multiplication-Sign 10{sup 32} erg s{sup -1}{approx}0.0036 E-dot for a distance of 6.1 kpc. We detect no X-ray pulsations from the source, setting a 1{sigma} upper limit on the pulsed fraction of 60% in the 0.5-3 keV band. We compare PSR J1734-3333 to other rotation-powered pulsars of similar age and find that it is significantly hotter, supporting the hypothesis that the magnetic field affects the observed thermal properties of pulsars. We also report on XMM-Newton and Chandra observations of PSRs B1845-19 and J1001-5939. We do not detect either pulsar, setting 3{sigma} upper limits on their blackbody temperatures of 48 and 56 eV, respectively. Despite the similarities in rotational properties, these sources are significantly cooler than all but one of the XINSs, which we attribute to the two groups having been born with different magnetic fields and hence evolving differently.

  20. A study of multifrequency polarization pulse profiles of millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Dai, S.; Hobbs, G.; Manchester, R. N.; Kerr, M.; Shannon, R. M.; van Straten, W.; Mata, A.; Bailes, M.; Bhat, N. D. R.; Burke-Spolaor, S.; Coles, W. A.; Johnston, S.; Keith, M. J.; Levin, Y.; Osłowski, S.; Reardon, D.; Ravi, V.; Sarkissian, J. M.; Tiburzi, C.; Toomey, L.; Wang, H. G.; Wang, J.-B.; Wen, L.; Xu, R. X.; Yan, W. M.; Zhu, X.-J.

    2015-05-01

    We present high signal-to-noise ratio, multifrequency polarization pulse profiles for 24 millisecond pulsars that are being observed as part of the Parkes Pulsar Timing Array project. The pulsars are observed in three bands, centred close to 730, 1400 and 3100 MHz, using a dual-band 10 cm/50 cm receiver and the central beam of the 20-cm multibeam receiver. Observations spanning approximately six years have been carefully calibrated and summed to produce high S/N profiles. This allows us to study the individual profile components and in particular how they evolve with frequency. We also identify previously undetected profile features. For many pulsars we show that pulsed emission extends across almost the entire pulse profile. The pulse component widths and component separations follow a complex evolution with frequency; in some cases these parameters increase and in other cases they decrease with increasing frequency. The evolution with frequency of the polarization properties of the profile is also non-trivial. We provide evidence that the pre- and post-cursors generally have higher fractional linear polarization than the main pulse. We have obtained the spectral index and rotation measure for each pulsar by fitting across all three observing bands. For the majority of pulsars, the spectra follow a single power-law and the position angles follow a λ2 relation, as expected. However, clear deviations are seen for some pulsars. We also present phase-resolved measurements of the spectral index, fractional linear polarization and rotation measure. All these properties are shown to vary systematically over the pulse profile.

  1. Mid- and Far-Infrared Infrared Space Observatory Limits on Dust Disks Around Millisecond Pulsars

    DTIC Science & Technology

    2004-05-12

    pulsars: general 1. INTRODUCTION The first extrasolar planets discovered were found around the millisecond pulsar PSR B1257+12 (Wolszczan & Frail...Observatory. The pulsar PSR B1257+12 is orbited by three planets , and other millisecond pulsars may be orbited by dust disks that represent planets ...disk would be coupled only weakly to the pulsar’s emission. If the planets around PSR B1257+12 are composed largely of metals, our limits are probably

  2. High-Altitude Emission from Pulsar Slot Gaps: The Crab Pulsar

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Stern, Julie V.; Dyks, Jaroslaw; Frackowiak, Michal

    2008-01-01

    We present results of a 3D model of optical to gamma-ray emission from the slot gap accelerator of a rotation-powered pulsar. Primary electrons accelerating to high-altitudes in the unscreened electric field of the slot gap reach radiation-reaction limited Lorentz factors of approx. 2 x 10(exp 7), while electron-positron pairs from lower-altitude cascades flow along field lines interior to the slot gap. The curvature, synchrotron and inverse Compton radiation of both primary electrons and pairs produce a broad spectrum of emission from infra-red to GeV energies. Both primaries and pairs undergo cyclotron resonant absorption of radio photons, allowing them to maintain significant pitch angles. Synchrotron radiation from pairs with a power-law energy spectrum from gamma = 10(exp 2) - 10(exp 5), dominate the spectrum up to approx. 10 MeV. Synchrotron and curvature radiation of primaries dominates from 10 MeV up to a few GeV. We examine the energy-dependent pulse profiles and phase-resolved spectra for parameters of the Crab pulsar as a function of magnetic inclination alpha and viewing angle zeta, comparing to broad-band data. In most cases, the pulse profiles are dominated by caustics on trailing field lines. We also explore the relation of the high-energy and the radio profiles, as well as the possibility of caustic formation in the radio cone emission. We find that the Crab pulsar profiles and spectrum can be reasonably well reproduced by a model with alpha = 45deg and zeta approx. 100deg or 80deg. This model predicts that the slot gap emission below 200 MeV will exhibit correlations in time and phase with the radio emission.

  3. Numerical MHD modelling of composite SNR: The effect of pulsar birth period on pulsar wind parameters

    NASA Astrophysics Data System (ADS)

    de Jager, Ocker

    The γ-ray flux Fγ of a pulsar wind nebula in the GLAST/LAT domain can be shown to depend 2 on the pulsar birth period P0 as Fγ ∝ 1/P0 . Furthermore, it is also known that the PWN size depends on P0 , with the PWN radius overtaking the SNR forward shock if P0 is in the few millisecond domain. Whereas this is an interesting field of study, longer birth periods lead to slower PWN expansion, in which case the reverse shock compresses the PWN, One can therefore follow the time history of adiabatic losses versus adiabatic heating, which is important for multiwavelength modelling. We model composite SNRs as the time evolution of a PWN with its associated SNR forward/reverse shock and reflection wave. The effect of magnetic field is included via Faraday's induction equation. A high resolution numerical simulation scheme is followed whereby the explosion of a SNR with total explosion energy Esnr , ejecta mass Mej , ISM density ρISM and PWN energy via its pulsar birth period P0 , are followed through the Euler equations, describing inviscid flow. They are solved giving ρi (density), vi (velocity) and Pi (the pressure) with time. These equations correspond to the Navier-Stokes equations with zero viscosity and heat conduction terms. They describe the balance of mass, momentum and energy of different fluids, e.g. i = 1, 2, 3, ... and the interaction between these fluids are described by a source term Q(t), which, in the case of the PWN, is described by the spindown of the pulsar. We consider a two fluid scenario with non-relativistic (SNR) and relativistic (PWN) speeds (i = 1, 2), i.e. adiabatic indices of 5/3 and 4/3 respectively. The compressed ISM magnetic field is calculated through Faraday's Law. Note however that this is not a full MHD treatment since no backreaction on the fluid is considered. For the SNR we only consider the field of the ISM which gets compressed as the ISM is swept-up by the forward shock of the SNR. The same induction equation is also used to

  4. Pulsars above 10 GeV: Fermi LAT Observations and Questions

    NASA Technical Reports Server (NTRS)

    Thomson, Dave

    2012-01-01

    The success of the Fermi Large Area Telescope in studying gamma-ray pulsars offers hints about future work above 10 GeV. The infrastructure for discovering pulsars will be similar between LAT and any future telescope. Some of the Fermi LAT results suggest intriguing questions about the future of high-energy pulsar studies.

  5. Neutron Star Seismology with Accreting Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod

    Neutron stars provide natural laboratories for the study of a number of important topics in fundamental physics, including the composition and equation of state (EOS) of cold matter at the highest densities achievable in nature. The physical conditions in their deep interiors cannot be replicated in terrestrial laboratories, and the nature of matter under such extreme conditions remains one of the major unsolved problems in physics. Direct measurement of the mass - radius relationship for neutron stars is very important for constraining the EOS of dense matter, however, since different phases of dense matter can have similar equations of state, mass and radius measurements alone are not very efficient in determining their interior composition. Additional, complementary observables are needed to more definitively probe the composition of neutron star cores. Asteroseismology, the measurement of the characteristic frequencies of the normal modes of oscillation of stars, can provide a powerful probe of their interiors. For example, helioseismology has provided unprecedented insights about the deep interior of the Sun. Comparable capabilities for neutron star seismology have not yet been achieved, but our recent work indicates that sensitive searches for the signatures of neutron star oscillations can be carried out using the high time resolution, pulse timing data obtained by the Rossi X-ray Timing Explorer (RXTE)-and in the case of a single source the XMM-Newton pn camera-from the population of accreting millisecond X-ray pulsars (AMXPs, Strohmayer & Mahmoodifar 2014a), and in some thermonuclear burst sources (Strohmayer & Mahmoodifar 2014b). It is the primary aim of this proposal to carry out the first such comprehensive search for global oscillation modes across this entire source class of neutron stars using approximately 6 M-sec of RXTE and 100 k-sec of XMMNewton archival data, and thereby significantly advance the nascent field of neutron star seismology. We will

  6. Newly Commissioned Green Bank Telescope Bags New Pulsars

    NASA Astrophysics Data System (ADS)

    2002-01-01

    Astronomers using the National Science Foundation's newly commissioned Robert C. Byrd Green Bank Telescope (GBT) have discovered a windfall of three previously undetected millisecond pulsars in a dense cluster of stars in the Milky Way Galaxy. The Green Bank Telescope The Robert C. Byrd Green Bank Telescope "This globular cluster, known as Messier 62, has been very well studied, and it would have been an exciting discovery to find just one new pulsar. The fact that we were able to detect three new pulsars at one time is simply remarkable," said Bryan Jacoby, a graduate student at the California Institute of Technology who led the research team. Results of the discovery were recently announced in an International Astronomical Union Circular. Jacoby and his colleague Adam Chandler, also a graduate student at Caltech, used the GBT to search for new pulsars in addition to the three already known in this cluster. Their research was part of the GBT's Early Science Program, which allows scientific investigations during the testing and commissioning of the telescope. The researchers used the Berkeley-Caltech Pulsar Machine, a new instrument whose development was overseen by Donald Backer at the University of California at Berkeley, to process the signals from the GBT and record them for later analysis. After their data were analyzed, the researchers discovered the telltale signatures of three additional pulsars and their white dwarf companion stars. Pulsars are rapidly rotating neutron stars that emit intense beams of radio waves along their misaligned magnetic axes. When these beams intersect the Earth, we see the pulsar flash on and off. Due to their exquisitely steady rotation, pulsars allow astronomers to study the basic laws of physics and the ways in which these dense clusters and exotic stellar systems are formed. Astronomers study globular clusters because they are among the oldest building blocks of our Galaxy. With their very dense stellar populations, these

  7. State-of-art pulsar studies using interferometric arrays

    NASA Astrophysics Data System (ADS)

    Roy, Jayanta

    The new flexible and powerful software back-end (GSB) opens up the possibility of new regimes of pulsar studies with interferometric arrays like the GMRT, as exemplified by two unique techniques - a gating correlator for millisecond pulsars (MSPs) and a multi-pixel beamformer. We have developed a coherently dedispersed MSP gating correlator at the GMRT motivated by the requirement of localising the newly discovered faint Fermi MSPs. This imaging technique uses the dedispersed visibility data folded with period, acceleration and jerk. We could localise the tighter and fainter binary MSPs in the ON-OFF image plane, even outside the HPBW of GMRT. This tool enables study of unique aspects of MSP population (also pulsars in general) using present and up-coming interferometric arrays (LEAP, ASKAP, MeerKAT, SKA etc). Study the off-pulse emission from the gamma-ray selected MSPs using the MSP gating imaging technique can provide additional constrain on the emission region in pulsar magnetosphere. Moreover, proper motion study of the fainter pulsars is highly benefited from the sensitivity enhancement on the gated image plane. We have also developed a multi-pixel beamformer technique, which is able to look for pulsations much more efficiently over a larger solid angle. This efficient technique combines the enhanced sensitivity of a coherent array beamformer with the wide field-of-view seen by an incoherent array beamformer. I will present a special application of this technique, where we use continuum imaging followed by the multi-pixel beamformer to obtain the precise locations of newly discovered MSPs with the GMRT. Accurate positions measured with single observations enable highly sensitive follow-up studies using coherent array beamformer and rapid follow up at higher radio frequencies and other wavelengths. Normally, such accurate positions can only be obtained from a long-term pulsar timing program. The multi-pixel beamformer technique can also be used for highly

  8. a Surprise from the Pulsar in the Crab Nebula

    NASA Astrophysics Data System (ADS)

    1995-11-01

    New observations of the spectrum of the rapidly spinning neutron star (the `pulsar') in the Crab Nebula have been carried out with the ESO 3.5-metre New Technology Telescope (NTT) by a group of Italian astronomers [1]. Because of greatly improved spectral resolution which allows to register even very fine details in the pulsar's spectrum, they are able to determine for the first time with high accuracy the overall dependance of the emission on wavelength, i.e. the `shape' of the spectrum. Quite unexpectedly, they also detect a hitherto unknown 100 A (10 nm) broad `absorption dip', which can be securely attributed to the pulsar. These results open an exciting new window for the study of the extreme physical processes close to a pulsar. The Nature of Pulsars It is estimated that there may be as many as 100 million neutron stars in our Galaxy. A neutron star is the superdense remnant of the extremely violent supernova explosion that occurs at the end of the life of a comparatively massive star. In fact, all stars that are more than about 6 times heavier than the Sun are believed to end their lives as supernovae. During the explosion, the central core of the dying star collapses in a few milliseconds and the matter at the centre is compressed to a density comparable to that of an atomic nucleus. Due to the enormous inward pressure, the atomic particles are squeezed together into a kind of neutron jam. The outcome is the formation of a neutron star with a diameter of 10-15 kilometres, weighing as much as the Sun. In accordance with the physical law that implies that the rotation momentum of the exploding star must be conserved, newborn neutron stars will rotate very rapidly around their axis, in some cases as fast as 100 times per second. In the same way, the new neutron star is expected to possess a strong magnetic field. Of these myriads of neutron stars, about 700 have been observed to emit radio pulses (hence the name `pulsar'). A few of these can also be detected

  9. Motion of charged particles in pulsar magnetospheres

    NASA Astrophysics Data System (ADS)

    Zachariades, Haris Andrea

    The motion of charges in the magnetosphere of pulsars is studied from two complementary points of view: (1) for the case of aligned magnetic and rotational axes we solve a fluid version of the Lorentz-Dirac equation, in the Landau approximation, for a two-component plasma. We start from an approximately force-free initial condition and numerically integrate the equations of motion for a time equal to 1.6 percent of one stellar rotation period. We find that the system tends to a charge-separated state in which a negative charge region above the poles is separated by a vacuum gap from a positive charge region near the equator. We see the formation of force-free regions and a tendency of the vacuum gap to spread as the integrations proceed. The energies attained by the charges are only mildly relativistic and radiation reaction does not play an important role during the integrations. The negative charge above the polar region is electrostatically bound and there is a force-free region towards which negative charge tends to flow. Some positive charge is magnetically confined near the stellar equator and other positive charge crosses magnetic field lines moving outward to the region beyond the light cylinder. The outward motion of positive charge is due to the relative magnitudes of the electric and magnetic fields. (2) For the case of non-aligned axes we study the single particle dynamics for electrons moving in the region beyond the light cylinder, again using the Landau approximation to the Lorentz-Dirac equation. The effect of the inner magnetosphere is taken into account by adding a central attractive charge. We find that there exists a class of solutions corresponding to bounded orbits beyond the light cylinder. In an independent particle picture, particles started with different initial conditions within the basin of attraction of this class of orbits eventually form corotating patterns beyond the light cylinder. For a frequently occurring particle configuration

  10. THE GALACTIC POPULATION OF YOUNG {gamma}-RAY PULSARS

    SciTech Connect

    Watters, Kyle P.; Romani, Roger W. E-mail: rwr@astro.stanford.edu

    2011-02-01

    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{sub 0} {approx} 50 ms and {gamma}-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 {gamma}-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 {gamma}-ray background.

  11. Hunting for Orphaned Central Compact Objects among Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Luo, J.; Ng, C.-Y.; Ho, W. C. G.; Bogdanov, S.; Kaspi, V. M.; He, C.

    2015-08-01

    Central compact objects (CCOs) are a handful of young neutron stars found at the center of supernova remnants (SNRs). They show high thermal X-ray luminosities but no radio emission. Spin-down rate measurements of three CCOs with X-ray pulsations indicate surface dipole fields much weaker than those of typical young pulsars. To investigate if CCOs and known radio pulsars are objects at different evolutionary stages, we carried out a census of all weak-field (\\lt {10}11 G) isolated radio pulsars in the Galactic plane to search for CCO-like X-ray emission. None of the 12 candidates are detected at X-ray energies, with luminosity limits of {10}32-{10}34 erg s-1. We consider a scenario in which the weak surface fields of CCOs are due to a rapid accretion of supernova materials and show that as the buried field diffuses back to the surface, a CCO descendant is expected to leave the P-\\dot{P} parameter space of our candidates at a young age of a few ×10 kyr. Hence, the candidates are likely to just be old ordinary pulsars in this case. We suggest that further searches for orphaned CCOs, which are aged CCOs with parent SNRs that have dissipated, should include pulsars with stronger magnetic fields.

  12. THREE MILLISECOND PULSARS IN FERMI LAT UNASSOCIATED BRIGHT SOURCES

    SciTech Connect

    Ransom, S. M.; Ray, P. S.; Wolff, M. T.; Grove, J. E.; Camilo, F.; Roberts, M. S. E.; Celik, Oe.; DeCesar, M. E.; Ferrara, E. C.; Gehrels, N.; Cheung, C. C.; Abdo, A. A.; Kerr, M.; Pennucci, T.; Cognard, I.; Freire, P. C. C.; Desvignes, G.; Donato, D. E-mail: Paul.Ray@nrl.navy.mil

    2011-01-20

    We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. We report the discovery of three radio and {gamma}-ray millisecond pulsars (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind {gamma}-ray pulsation searches. They seem to be relatively normal, nearby ({<=}2 kpc) MSPs. These observations, in combination with the Fermi detection of {gamma}-rays from other known radio MSPs, imply that most, if not all, radio MSPs are efficient {gamma}-ray producers. The {gamma}-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few GeV, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Their soft X-ray luminosities of {approx}10{sup 30}-10{sup 31} erg s{sup -1} are typical of the rare radio MSPs seen in X-rays.

  13. Observations of pulsar microstructure with the Giant Metrewave Radio Telescope

    NASA Astrophysics Data System (ADS)

    de, Kishalay; Gupta, Yashwant; Sharma, Prateek

    2017-01-01

    Microstructure emission, involving short time scale intensity fluctuations in subpulse emission, is well known in normal pulsars. However, the high time resolution and sensitivity required to detect these features has limited such studies to only few pulsars, mostly in the northern sky. The Giant Metrewave Radio Telescope (GMRT), owing to its high sensitivity, extensive sky coverage and frequency coverage at low frequencies is an attractive prospect for high time resolution single pulse studies of pulsars. In this paper, we present results from an extensive statistical analysis of the polarization (with single frequency observations) and spectral (with simultaneous dual-frequency observations) properties of microstructure emission in pulsars observed with the GMRT. We further present the first detections of quasi-periodic microstructure emission from millisecond pulsars (MSPs), in GMRT observations of two MSPs at 325 and 610 MHz. We thus extend the microstructure timescale - rotation period relationship by more than an order of magnitude, down to a rotation period of 5 ms. We discuss the physical implications of our results, pointing to a radial / temporal modulation origin of microstructure emission as a likely explanation for the observed characteristics.

  14. Tests of general relativity from timing the double pulsar.

    PubMed

    Kramer, M; Stairs, I H; Manchester, R N; McLaughlin, M A; Lyne, A G; Ferdman, R D; Burgay, M; Lorimer, D R; Possenti, A; D'Amico, N; Sarkissian, J M; Hobbs, G B; Reynolds, J E; Freire, P C C; Camilo, F

    2006-10-06

    The double pulsar system PSR J0737-3039A/B is unique in that both neutron stars are detectable as radio pulsars. They are also known to have much higher mean orbital velocities and accelerations than those of other binary pulsars. The system is therefore a good candidate for testing Einstein's theory of general relativity and alternative theories of gravity in the strong-field regime. We report on precision timing observations taken over the 2.5 years since its discovery and present four independent strong-field tests of general relativity. These tests use the theory-independent mass ratio of the two stars. By measuring relativistic corrections to the Keplerian description of the orbital motion, we find that the "post-Keplerian" parameter s agrees with the value predicted by general relativity within an uncertainty of 0.05%, the most precise test yet obtained. We also show that the transverse velocity of the system's center of mass is extremely small. Combined with the system's location near the Sun, this result suggests that future tests of gravitational theories with the double pulsar will supersede the best current solar system tests. It also implies that the second-born pulsar may not have formed through the core collapse of a helium star, as is usually assumed.

  15. Searches for Pulsars at the Center of the Galaxy

    NASA Astrophysics Data System (ADS)

    Majid, Walid

    2015-08-01

    Pulsars are highly magnetized, rapidly rotating neutron stars that emit a beam of electromagnetic radiation that could be detected at Earth, if the emission beam is pointing toward the Earth, analogous to the way a lighthouse can be seen when the light is pointed in the direction of the observer. Pulsars within the central parsec of our Galaxy is expected to make excellent probes of not only the environment of the supermassive black hole at the center of the galaxy, but also in the case of pulsar/black hole binary systems expected in this region, of their own rich environment dominated by relativistic gravity effects. In this presentation I will give an overview of why it is important to search for pulsars in the center of the galaxy, and a summary of previous and ongoing efforts to survey this region with radio telescopes. I will describe the difficulties encountered with current surveys and prospects for detection of perhaps hundreds of pulsars in this region with new generations of radio telescopes now under construction.

  16. Three Millisecond Pulsars in Fermi LAT Unassociated Bright Sources

    NASA Technical Reports Server (NTRS)

    Ransom, S. M.; Ray, P. S.; Camilo, F.; Roberts, M. S. E.; Celik, O.; Wolff, M. T.; Cheung, C. C.; Kerr, M.; Pennucci, T.; DeCesar, M. E.; Cognard, I.; Lyne, A. G.; Stappers, B. W.; Freire, P. C. C.; Grove, J. E.; Abdo, A. A.; Desvignes, G.; Donato, D.; Ferrara, E. C.; Gehrels, N.; Guillemot, L.; Gwon, C.; Johnston, S.; Harding, A. K.; Thompson, D. J.

    2010-01-01

    We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. We report the discovery of three radio and gamma-ray millisecond pulsar (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind gamma-ray pulsation searches. They seem to be relatively normal, nearby (<= 2 kpc) MSPs. These observations, in combination with the Fermi detection of gamma-rays from other known radio MSPs, imply that most, if not all, radio MSPs are efficient gamma-ray producers. The gamma-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few Ge V, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Their soft X-ray luminosities of approx 10(exp 30) - 10(exp 31) erg/s are typical of the rare radio MSPs seen in X-rays.

  17. DISCOVERY OF FIVE NEW PULSARS IN ARCHIVAL DATA

    SciTech Connect

    Mickaliger, M. B.; Collins, A.; Hough, L.; Tehrani, N.; Tenney, C.; Liska, A.; Swiggum, J.; Lorimer, D. R.; McLaughlin, M. A.; Boyles, J.

    2012-11-10

    Reprocessing of the Parkes Multibeam Pulsar Survey has resulted in the discovery of five previously unknown pulsars and several as-yet-unconfirmed candidates. PSR J0922-52 has a period of 9.68 ms and a dispersion measure (DM) of 122.4 pc cm{sup -3}. PSR J1147-66 has a period of 3.72 ms and a DM of 133.8 pc cm{sup -3}. PSR J1227-6208 has a period of 34.53 ms, a DM of 362.6 pc cm{sup -3}, is in a 6.7 day binary orbit, and was independently detected in an ongoing high-resolution Parkes survey by Thornton et al. and also in independent processing by Einstein-Home volunteers. PSR J1546-59 has a period of 7.80 ms and a DM of 168.3 pc cm{sup -3}. PSR J1725-3853 is an isolated 4.79 ms pulsar with a DM of 158.2 pc cm{sup -3}. These pulsars were likely missed in earlier processing efforts due to the fact that they have both high DMs and short periods, and also due to the large number of candidates that needed to be looked through. These discoveries suggest that further pulsars are awaiting discovery in the multibeam survey data.

  18. The Spectrum of LMC Pulsar B0540-69; Carryover

    NASA Astrophysics Data System (ADS)

    Bless, Robert

    1994-01-01

    PSR B0540-69, a 50 ms pulsar located in the Large Magellanic Cloud, is the most distant pulsar known. B0540-69 is one of the few pulsars for which a second time derivative of rotational frequency has been measured. High Speed Photometer observations in a UV + visible passband (1600 - 7000 angstroms) showed a pulse profile identical to that in the X-ray region, with the same pulsed fraction (van Citters et al 1994). The rotational frequency observed by HSP, when compared with previous measurements, gave a value of 2.28 (0.02) for the braking index. B0540-69 is similar to the Crab pulsar in its rotational perior and associated synchrotron-emitting nebula (a "plerion"), but its pulse profile and braking index are strikingly different. We propose her to obtain an objective prism spectrum of B0540-69 to compare its spectral energy distribution in the UV and blue with that of the Crab pulsar and to determine the fractional part of our UV plus visible pulse profile due to UV photons. Our objective prism spectrum with the FOS Blue detector will measure the relative energy distribution between ~1850 and ~5000 angstroms.

  19. Study of band inversion in the PbxSn1-xTe class of topological crystalline insulators using x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Mitrofanov, K. V.; Kolobov, A. V.; Fons, P.; Krbal, M.; Tominaga, J.; Uruga, T.

    2014-11-01

    PbxSn1-xTe and PbxSn1-xSe crystals belong to the class of topological crystalline insulators where topological protection is achieved due to crystal symmetry rather than time-reversal symmetry. In this work, we make use of selection rules in the x-ray absorption process to experimentally detect band inversion along the PbTe(Se)-SnTe(Se) tie-lines. The observed significant change in the ratio of intensities of L1 and L3 transitions along the tie-line demonstrates that x-ray absorption can be a useful tool to study band inversion in topological insulators.

  20. X-ray photoelectron spectroscopy and atomic force microscopy characterization of the effects of etching Zn xCd 1- xTe surfaces

    NASA Astrophysics Data System (ADS)

    George, M. A.; Azoulay, M.; Jayatirtha, H. N.; Burger, A.; Collins, W. E.; Silberman, E.

    1993-10-01

    X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) was used for the first time to characterize the chemical composition of modified surfaces of Zn xCd 1- xTe single crystals. These surface treatments were selected for their relevance to device preparation procedures. The XPS peaks indicated an increase of the tellurium and a depletion of the cadmium concentrations upon etching in bromine methanol solution. AFM revealed the formation of pronounced Te inclusions. Higher x values correlated with a decrease in residual bromine left on the surface, while cut and polished samples had higher oxide concentrations and increased bromination of the surface than cleaved samples.

  1. Hydrodynamic simulations of pulsar glitch recovery

    NASA Astrophysics Data System (ADS)

    Howitt, G.; Haskell, B.; Melatos, A.

    2016-08-01

    Glitches are sudden jumps in the spin frequency of pulsars believed to originate in the superfluid interior of neutron stars. Superfluid flow in a model neutron star is simulated by solving the equations of motion of a two-component superfluid consisting of a viscous proton-electron plasma and an inviscid neutron condensate in a spherical Couette geometry. We examine the response of the model to glitches induced in three different ways: by instantaneous changes of the spin frequency of the inner and outer boundaries, and by instantaneous recoupling of the fluid components in the bulk. All simulations are performed with strong and weak mutual friction. It is found that the maximum size of a glitch originating in the bulk decreases as the mutual friction strengthens. It is also found that mutual friction determines the fraction of the frequency jump which is later recovered, a quantity known as the `healing parameter'. These behaviours may explain some of the diversity in observed glitch recoveries.

  2. Statistical summaries of polarized pulsar radiation

    SciTech Connect

    Backer, D.C.; Rankin, J.M.

    1980-01-01

    This paper considers the polarization behavior of 18 pulsars as observed at 430 MHz in the Arecibo Polarization Survey. The results following from a statistical analysis are presented as probability of occurrence histograms at a series of pulse longitudes, with the signal being characterized by its total intensity, fractional linear polarization and angel, and fractional circular polarization. The statistical summary displays then provide a much more comprehensive delineation of polarization characteristics than the usual average Stokes parameters.The displays leave no room for doubt as to the central role of the polarization (states or) modes: two modes are active at one longitude or another in virtually every object, and their vacillating dominance with longitude seriously disrupts the average angle behavior in about half the cases. This is to say that, while the average angle behavior is often inconsistent with the rotating-vector (Radhakrishnan and Cooke) model, the individual modes generally exhibit rotations which accord rather closely with the model.We further consider the angular separation of the two modes and encounter several apparently significant cases of nonorthogonality. Evidence for weak intensity-dependent polarizations is encountered in both the linear and circular histograms. The angle displays provide a basis for investigating the nature of the depolarization known to exist at 430 MHz. We finally consider two objects which exhibit complex angle behavior and speculate on the properties of a more general rotating-vector model consistent with them.

  3. Gross-Pitaevskii model of pulsar glitches

    NASA Astrophysics Data System (ADS)

    Warszawski, L.; Melatos, A.

    2011-08-01

    The first large-scale quantum mechanical simulations of pulsar glitches are presented, using a Gross-Pitaevskii model of the crust-superfluid system in the presence of pinning. Power-law distributions of simulated glitch sizes are obtained, in accord with astronomical observations, with exponents ranging from -0.55 to -1.26. Examples of large-scale simulations, containing ˜200 vortices, reveal that these statistics persist in the many-vortex limit. Waiting-time distributions are also constructed. These and other statistics support the hypothesis that catastrophic unpinning mediated by collective vortex motion produces glitches; indeed, such collective events are seen in time-lapse movies of superfluid density. Three principal trends are observed. (1) The glitch rate scales proportional to the electromagnetic spin-down torque. (2) A strong positive correlation is found between the strength of vortex pinning and mean glitch size. (3) The spin-down dynamics depend less on the pinning site abundance once the latter exceeds one site per vortex, suggesting that unpinned vortices travel a distance comparable to the intervortex spacing before repinning.

  4. Unpulsed Optical Emission from the Crab Pulsar

    NASA Astrophysics Data System (ADS)

    Golden, A.; Shearer, A.; Beskin, G. M.

    2000-05-01

    Based on observations of the Crab pulsar using the TRIFFID high-speed imaging photometer in the UBV bands using the Special Astrophysical Observatory's 6 m telescope in the Russian Caucasus, we report the detection of pronounced emission during the so-called off phase of emission. Following de-extinction, this unpulsed component of emission is shown to be consistent with a power law with an exponent of α=-0.60+/-0.37, the uncertainty being dominated by the error associated with the independent CCD photometry used to reference the TRIFFID data. This suggests a steeper power-law form than that reported elsewhere in the literature for the total integrated spectrum, which is essentially flat with α~0.1, although the difference in this case is only significant at the <=2 σ level. Deeper reference integrated and TRIFFID phase-resolved photometry, in these bands in conjunction with further observations in the UV and R region, would constrain this fit further. Based on observations using the 6 m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences in Nizhnii Arkhyz, Russia.

  5. Gamma-Ray Signal from the Pulsar Wind in the Binary Pulsar System PSR B1259-63/LS 2883

    NASA Astrophysics Data System (ADS)

    Khangulyan, Dmitry; Aharonian, Felix A.; Bogovalov, Sergey V.; Ribó, Marc

    2011-12-01

    Binary pulsar systems emit potentially detectable components of gamma-ray emission due to Comptonization of the optical radiation of the companion star by relativistic electrons of the pulsar wind, both before and after termination of the wind. The recent optical observations of binary pulsar system PSR B1259-63/LS 2883 revealed radiation properties of the companion star which differ significantly from previous measurements. In this paper, we study the implications of these observations for the interaction rate of the unshocked pulsar wind with the stellar photons and the related consequences for fluxes of high energy and very high energy (VHE) gamma rays. We show that the signal should be strong enough to be detected with Fermi close to the periastron passage, unless the pulsar wind is strongly anisotropic or the Lorentz factor of the wind is smaller than 103 or larger than 105. The higher luminosity of the optical star also has two important implications: (1) attenuation of gamma rays due to photon-photon pair production and (2) Compton drag of the unshocked wind. While the first effect has an impact on the light curve of VHE gamma rays, the second effect may significantly decrease the energy available for particle acceleration after termination of the wind.

  6. GAMMA-RAY SIGNAL FROM THE PULSAR WIND IN THE BINARY PULSAR SYSTEM PSR B1259-63/LS 2883

    SciTech Connect

    Khangulyan, Dmitry; Bogovalov, Sergey V.; Ribo, Marc E-mail: felix.aharonian@dias.ie E-mail: mribo@am.ub.es

    2011-12-01

    Binary pulsar systems emit potentially detectable components of gamma-ray emission due to Comptonization of the optical radiation of the companion star by relativistic electrons of the pulsar wind, both before and after termination of the wind. The recent optical observations of binary pulsar system PSR B1259-63/LS 2883 revealed radiation properties of the companion star which differ significantly from previous measurements. In this paper, we study the implications of these observations for the interaction rate of the unshocked pulsar wind with the stellar photons and the related consequences for fluxes of high energy and very high energy (VHE) gamma rays. We show that the signal should be strong enough to be detected with Fermi close to the periastron passage, unless the pulsar wind is strongly anisotropic or the Lorentz factor of the wind is smaller than 10{sup 3} or larger than 10{sup 5}. The higher luminosity of the optical star also has two important implications: (1) attenuation of gamma rays due to photon-photon pair production and (2) Compton drag of the unshocked wind. While the first effect has an impact on the light curve of VHE gamma rays, the second effect may significantly decrease the energy available for particle acceleration after termination of the wind.

  7. The search for MeV gamma-ray pulsars with COMPTEL

    NASA Technical Reports Server (NTRS)

    Bennett, K.; Buccheri, R.; Busetta, M.; Carraminana, A.; Connors, A.; Diehl, R.; Hermsen, W.; Kuiper, L.; Lichti, G. G.; Much, R.

    1995-01-01

    The Compton Gamma Ray Observatory (CGRO) completed a full sky survey in November 1993 during which the number of known gamma-ray pulsars more than doubled. During this survey the Compton Telescope (COMPTEL) observed the classical isolated pulsars Crab and Vela and detected PSR 1509-58. Attempts to detect the newly discovered pulsars, Geminga, PSR 1706-44 and PSR 1055-52, in the COMPTEL energy range provide only upper limits. The results of these analyses are presented together with the outcome of a search for further candidate radio pulsars whose ephemerides are given in the Princeton Pulsar Catalogue.

  8. When will a pulsar in supernova 1987a be seen?

    PubMed

    Michel, F C; Kennel, C F; Fowler, W A

    1987-11-13

    The means by which a pulsar might be detected in the remnant of supernova 1987a in the Large Magelanic Cloud is examined. One possibility is that the slower-than-radioactive decay typically seen in the type II light curves is itself the sign of powering by the underlying pulsar, with the decline representing not the spinning down of the pulsar but rather the declining nebular opacity that would allow increasing amounts of the energy to escape as gamma rays. The test of this hypothesis (if the supernova conforms to type II expectations) would be to look for the "missing" energy in the form of those gamma rays that escape from the remnant instead of powering it.

  9. When will a pulsar in supernova 1987a be seen?

    NASA Technical Reports Server (NTRS)

    Michel, F. Curtis; Kennel, C. F.; Fowler, William A.

    1987-01-01

    The means by which a pulsar might be detected in the remnant of supernova 1987a in the Large Magellanic Cloud is examined. One possibility is that the slower-than-radioactive decay typically seen in the type II light curves is itself the sign of powering by the underlying pulsar, with the decline representing not the spinning down of the pulsar but rather the declining nebular opacity that would allow increasing amounts of the energy to escape as gamma rays. The test of this hypothesis (if the supernova conforms to type II expectations) would be to look for the 'missing' energy in the form of those gamma rays that escape from the remnant instead of powering it.

  10. Detection of Hidden Pulsar J0737-3039B

    NASA Astrophysics Data System (ADS)

    Maynard, Tessa

    2016-01-01

    The double pulsar system, PSR J0737-3039, contains companions PSR J0737-3039A & PSR J0737-3039B, which rotate at 23 ms and 2.8 respectively. As of March 2008 pulsar B's radio signal disappeared, with previous decreases in flux density by 0.177 mJy yr-1 and evolving pulse profile seperation of 2fdg6 yr-1 from a single peak to a double peak. Models using the system's relativistic spin precession have predicted the reappearance of PSR J0737-3039B in approximately 2014 or 2035. Using data from the Green Bank telescope we attempt to redetect pulsar B and explain the mechanics of its disappearance.

  11. An Active, Asynchronous Companion to a Redback Millisecond Pulsar

    NASA Astrophysics Data System (ADS)

    van Staden, André D.; Antoniadis, John

    2016-12-01

    PSR J1723-2837 is a “redback” millisecond pulsar (MSP) with a low-mass companion in a 14.8 hr orbit. The system’s properties closely resemble those of “transitional” MSPs that alternate between spin-down and accretion-powered states. In this Letter, we report on long-term photometry of the 15.5 mag companion to the pulsar. We use our data to illustrate that the star experiences sporadic activity, which we attribute to starspots. We also find that the companion is not tidally locked and infer {P}{{s}}/{P}{{b}}=0.9974(7) for the ratio between the rotational and orbital periods. Finally, we place constraints on various parameters, including the irradiation efficiency and pulsar mass. We discuss similarities with other redback MSPs and conclude that starspots may provide the most likely explanation for the often seen irregular and asymmetric optical light curves.

  12. Spatial Distribution of Pair Production Over the Pulsar Polar Cap

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail A.; Parfrey, Kyle

    2016-10-01

    Using an analytic, axisymmetric approach that includes general relativity, coupled to a condition for pair production deduced from simulations, we derive general results about the spatial distribution of pair-producing field lines over the pulsar polar cap. In particular, we show that pair production on magnetic field lines operates over only a fraction of the polar cap for an aligned rotator for general magnetic field configurations, assuming the magnetic field varies spatially on a scale that is larger than the size of the polar cap. We compare our result to force-free simulations of a pulsar with a dipole surface field and find excellent agreement. Our work has implications for first-principles simulations of pulsar magnetospheres and for explaining observations of pulsed radio and high-energy emission.

  13. Pinning down the superfluid and measuring masses using pulsar glitches

    PubMed Central

    Ho, Wynn C. G.; Espinoza, Cristóbal M.; Antonopoulou, Danai; Andersson, Nils

    2015-01-01

    Pulsars are known for their superb timing precision, although glitches can interrupt the regular timing behavior when the stars are young. These glitches are thought to be caused by interactions between normal and superfluid matter in the crust of the star. However, glitching pulsars such as Vela have been shown to require a superfluid reservoir that greatly exceeds that available in the crust. We examine a model in which glitches tap the superfluid in the core. We test a variety of theoretical superfluid models against the most recent glitch data and find that only one model can successfully explain up to 45 years of observational data. We develop a new technique for combining radio and x-ray data to measure pulsar masses, thereby demonstrating how current and future telescopes can probe fundamental physics such as superfluidity near nuclear saturation. PMID:26601293

  14. Measuring the Spin Period of a High-Velocity Pulsar

    NASA Astrophysics Data System (ADS)

    Tomsick, John

    2012-10-01

    X-ray observations of IGR J11014-6103 show that it has a complex morphology with a point source and two components of extended emission. Its properties indicate that it is very likely to be a pulsar wind nebula (PWN). Chandra and radio observations strongly suggest that the compact object is moving away from SNR MSH 11-61A. Based on the evolution of this supernova remnant, an association would indicate that IGR J11014-6103 has a transverse velocity of 2,400 to 2,900 km/s. The possibility of such a high kick velocity makes the proposed timing study important for proving that the compact object is a pulsar, determining its period (P), and measuring dP/dt to determine if the characteristic age is consistent with the pulsar originating in MSH 11-61A.

  15. The surprising Crab pulsar and its nebula: a review

    NASA Astrophysics Data System (ADS)

    Bühler, R.; Blandford, R.

    2014-06-01

    The Crab nebula and its pulsar (referred to together as ‘the Crab’) have historically played a central role in astrophysics. True to this legacy, several unique discoveries have been made recently. The Crab was found to emit gamma-ray pulsations up to energies of 400 GeV, beyond what was previously expected from pulsars. Strong gamma-ray flares, of durations of a few days, were discovered from within the nebula, while the source was previously expected to be stable in flux on these time scales. Here we review these intriguing and suggestive developments. In this context we give an overview of the observational properties of the Crab and our current understanding of pulsars and their nebulae.

  16. Gamma ray observations of the Crab pulsar - Past, present, future

    NASA Technical Reports Server (NTRS)

    Fishman, Gerald J.

    1992-01-01

    The paper describes some of the high-energy observations of the Crab-Nebula pulsar, PSR0531+22. The pulse profiles of the Crab pulsar obtained in balloon-borne observations in 1967 and 1980 are presented. At present, gamma-ray scintillation detectors aboard the Gamma Ray Observatory (GRO) form the basis of the Burst and Transient Source Experiment (BATSE). The pulsar, which is observed daily by the BATSE, is used by all four GRO/BATSE detectors as a calibration source since it emits a steady, strong, well-known spectrum of gamma rays over the entire energy range to which detectors are sensitive. The paper presents an example of a pulse profile obtained with the BATSE.

  17. Pulsar timing arrays: closing in on low- frequency gravitational waves

    NASA Astrophysics Data System (ADS)

    Sampson, Laura

    2017-01-01

    Just like electromagnetic radiation, gravitational waves come in a wide spectrum of frequencies. Different frequencies give us access to different physical information about our universe. By taking advantage of the phenomenal stability of the spin rate of millisecond pulsars, pulsar timing arrays will allow us to detect gravitational waves in the nanohertz band. The most likely source in this band is supermassive black hole binaries, formed when galaxies merge, and so the detection of these gravitational waves gives us a new tool to learn about the merger history of galaxies and the environment in galactic cores. I will discuss the exciting astrophysics we can learn using pulsar timing arrays, as well as the prospects and expected timeline for gravitational wave detection in this new frequency regime.

  18. Modelling pulsar glitches with realistic pinning forces: a hydrodynamical approach

    NASA Astrophysics Data System (ADS)

    Haskell, B.; Pizzochero, P. M.; Sidery, T.

    2012-02-01

    Although pulsars are some of the most stable clocks in the Universe, many of them are observed to 'glitch', i.e. to suddenly increase their spin frequency ? with fractional increases that range from ? to ?. In this paper, we focus on the 'giant' glitches, i.e. glitches with fractional increases in the spin rate of the order of ?, that are observed in a subclass of pulsars including the Vela. We show that giant glitches can be modelled with a two-fluid hydrodynamical approach. The model is based on the formalism for superfluid neutron stars of Andersson & Comer and on the realistic pinning forces of Grill & Pizzochero. We show that all stages of Vela glitches, from the rise to the post-glitch relaxation, can be reproduced with a set of physically reasonable parameters and that the sizes and waiting times between giant glitches in other pulsars are also consistent with our model.

  19. The surprising Crab pulsar and its nebula: a review.

    PubMed

    Bühler, R; Blandford, R

    2014-06-01

    The Crab nebula and its pulsar (referred to together as 'the Crab') have historically played a central role in astrophysics. True to this legacy, several unique discoveries have been made recently. The Crab was found to emit gamma-ray pulsations up to energies of 400 GeV, beyond what was previously expected from pulsars. Strong gamma-ray flares, of durations of a few days, were discovered from within the nebula, while the source was previously expected to be stable in flux on these time scales. Here we review these intriguing and suggestive developments. In this context we give an overview of the observational properties of the Crab and our current understanding of pulsars and their nebulae.

  20. A massive pulsar in a compact relativistic binary.

    PubMed

    Antoniadis, John; Freire, Paulo C C; Wex, Norbert; Tauris, Thomas M; Lynch, Ryan S; van Kerkwijk, Marten H; Kramer, Michael; Bassa, Cees; Dhillon, Vik S; Driebe, Thomas; Hessels, Jason W T; Kaspi, Victoria M; Kondratiev, Vladislav I; Langer, Norbert; Marsh, Thomas R; McLaughlin, Maura A; Pennucci, Timothy T; Ransom, Scott M; Stairs, Ingrid H; van Leeuwen, Joeri; Verbiest, Joris P W; Whelan, David G

    2013-04-26

    Many physically motivated extensions to general relativity (GR) predict substantial deviations in the properties of spacetime surrounding massive neutron stars. We report the measurement of a 2.01 ± 0.04 solar mass (M⊙) pulsar in a 2.46-hour orbit with a 0.172 ± 0.003 M⊙ white dwarf. The high pulsar mass and the compact orbit make this system a sensitive laboratory of a previously untested strong-field gravity regime. Thus far, the observed orbital decay agrees with GR, supporting its validity even for the extreme conditions present in the system. The resulting constraints on deviations support the use of GR-based templates for ground-based gravitational wave detectors. Additionally, the system strengthens recent constraints on the properties of dense matter and provides insight to binary stellar astrophysics and pulsar recycling.