Pulsar B1937 Research Articles

Probing cosmic plasma with giant radio pulses

VLBI observations of the Crab pulsar with the 64-m radio telescope at Kalyazin (Russia) and the 46-m radio telescope of the Algonquin Radio Observatory (Canada) at 2.2 GHz and single-dish observations of the millisecond pulsar B1937+21 with the GBT (USA) at 2.1 GHz were conducted to probe the interstellar medium and study the properties of giant pulses. The VLBI data were processed with a dedicated software correlator, which allowed us to obtain the visibility of single giant pulses. Two frequency scales of 50 and 450 kHz were found in the diffraction spectra of giant pulses from the Crab pulsar. The location of the scattering region was estimated to be close to the outer edge of the nebula. No correlation was found between the power spectra of giant pulses at left- and right-hand circular polarization. We explain this lack of correlation through the influence of the strong magnetic field on circularly polarized emission in the region close to the Crab pulsar. Combining the measurement of the decorrelation bandwidth with that of the scattering time of giant pulses for B1937+21, we found three frequency scales of 1.7, 3.8, and 16.5 MHz. The scattering time of giant pulses of B1937+21 at 2.1 GHz was found to be 40+-4 ns. We obtained an upper limit of the intrinsic width of giant pulses from B1937+21 of less than 8 ns. The frequency dependences of the scattering times for the Crab pulsar and PSR B1937+21 were found to be different. They are characterized by exponents of -3.5 and -4.2, respectively. We attribute the difference to the large influence of scattering in the Crab nebula.

The observed effect of the evolution of the inclination angle of a radio pulsar

It is shown that small glitches in the rotation period of the pulsar B1822-09 can be explained by changes in the shape of the neutron star when the shape becomes inconsistent with the rotation axis, i.e., when the symmetry axis does not coincide with the instantaneous rotation axis. Due to variations of the angle between the rotation axis and the instantaneous dipole axis due to the decreasing momentum, the angle α between the rotation axis and the symmetry axis differs from zero. As a result of mechanical stress that develops in the neutron-star crust, this angle reaches its maximum value α ≈ 2 × 10−4, then returns to zero. This change in the shape of the neutron star is observed as a slow glitch in the frequency of the pulsar’s rotation.

High-Energy Particles in the Wind Nebula of Pulsar B1509-58 as Seen byINTEGRAL

We present observations with the INTEGRAL/IBIS telescope of the wind nebula powered by the young pulsar B1509-58 and we discuss the spatial and spectral properties of the unpulsed emission in the 20-200 keV energy band. The source extension and orientation along the northwest-southeast axis corresponds to the jet emission seen at keV and TeV energies. The hard X-ray spectrum is consistent with the earlier Beppo-SAX measurements. It follows a power law with a photon index alpha = -2.12 pm 0.05 up to 160 keV. A possible break at this energy is found at the 2.9 sigma confidence level. The 0.1-100 keV data are consistent with synchrotron aging of pairs in the jet and yield a magnetic field strength of 22-33 muG for a bulk velocity of 0.3-0.5c. The synchrotron cut-off energy thus corresponds to a maximum electron energy of 400-730 TeV.

Millisecond Pulsar Timing at Kalyazin Observatory

Pulsar timing of millisecond pulsars are carried on at Kalyazin radio astronomical observatory (Russia) since 1995. Seven pulsars are observed at 0.6 GHz by full steerable 64-m dish radio telescope RT-64 and filter-bank receiver. The millisecond pulsar B1937+21 is being monitored at Kalyazin observatory (0.6 GHz) and Kashima space research centre of NICT (Japan) (2.3 GHz), simultaneously since 1996.

Is Pulsar B0656+14 a Very Nearby Rotating Radio Transient?

The recently discovered RRAT sources are characterized by very bright radio bursts that, while being periodically related, occur infrequently. We find bursts with the same characteristics for the known pulsar B0656+14. These bursts represent pulses from the bright end of an extended smooth pulse-energy distribution and are shown to be unlike giant pulses, giant micropulses, or the pulses of normal pulsars. The extreme peak fluxes of the brightest of these pulses indicate that PSR B0656+14, were it not so near, could only have been discovered as an RRAT source. Longer observations of the RRATs may reveal that they, like PSR B0656+14, emit weaker emission in addition to the bursts.

CHECKING THE VARIABILITY OF THE GRAVITATIONAL CONSTANT WITH BINARY PULSARS

The most precise measurements are obtained at present by timing of radiopulsars in binary systems with two neutron stars. The timing measurements of the Taylor–Hulse pulsar B1913+16 gave the most precise results on testing of general relativity (GR), finding implicit proof of existence of gravitational waves. We show that the available results of existing measurements, obtained to the year 1993, in combination with the results of the Mariner 10 in 1992, give the boundaries for the variation of the gravitational constant Ġ/G (within) the limits (-0.6 –+2) × 10-12 yr -1.

Time Variability in the X‐Ray Nebula Powered by Pulsar B1509−58

We use new and archival Chandra and ROSAT data to study the time variability of the X-ray emission from the pulsar wind nebula (PWN) powered by PSR B1509-58 on timescales of one week to twelve years. There is variability in the size, number, and brightness of compact knots appearing within 20 of the pulsar, with at least one knot showing a possible outflow velocity of ~0.6c (assuming a distance to the source of 5.2 kpc). The transient nature of these knots may indicate that they are produced by turbulence in the flows surrounding the pulsar. A previously identified prominent jet extending 12 pc to the southeast of the pulsar increased in brightness by 30% over 9 years; apparent outflow of material along this jet is observed with a velocity of ~0.5c. However, outflow alone cannot account for the changes in the jet on such short timescales. Magnetohydrodynamic sausage or kink instabilities are feasible explanations for the jet variability with timescale of ~1.3-2 years. An arc structure, located 30-45 north of the pulsar, shows transverse structural variations and appears to have moved inward with a velocity of ~0.03c over three years. The overall structure and brightness of the diffuse PWN exterior to this arc and excluding the jet has remained the same over the twelve year span. The photon indices of the diffuse PWN and possibly the jet steepen with increasing radius, likely indicating synchrotron cooling at X-ray energies.

A Radio Pulsar Spinning at 716 Hz

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.

X‐Ray Emission from the Nearby PSR B1133+16 and Other Old Pulsars

We detected a nearby (d=360 pc), old (5 Myr) pulsar B1133+16 with Chandra. The observed pulsar's flux is $(0.8\pm 0.2)\times 10^{-14}$ ergs cm$^{-2}$ s$^{-1}$ in the 0.5-8 keV band. Because of the small number of counts detected, the spectrum can be described by various models. A power-law fit of the spectrum gives a photon index $\Gamma = 2.5$ and an isotropic luminosity of $1.4\times 10^{29}$ ergs s$^{-1}$ in the 0.5-8 keV band, which is about $1.6\times 10^{-3}$ of the spin-down power $\dot{E}$. The spectrum can also be fitted by a blackbody model with a temperature of $\approx 2.8$ MK and a projected emitting area of $\sim 500$ m$^2$, possibly a hot polar cap. The X-ray properties of PSR B1133+16 are similar to those of other old pulsars observed in X-rays, particularly the drifting pulsar B0943+10.

Giant pulses—The main component of the radio emission of the crab pulsar

The paper presents an analysis of dual-polarization observations of the Crab pulsar obtained on the 64-m Kalyazin radio telescope at 600 MHz with a time resolution of 250 ns. A lower limit for the intensities of giant pulses is estimated by assuming that the pulsar radio emission in the main pulse and interpulse consists entirely of giant radio pulses; this yields estimates of 100 Jy and 35 Jy for the peak flux densities of giant pulses arising in the main pulse and interpulse, respectively. This assumes that the normal radio emission of the pulse occurs in the precursor pulse. In this case, the longitudes of the giant radio pulses relative to the profile of the normal radio emission turn out to be the same for the Crab pulsar and the millisecond pulsar B1937+21, namely, the giant pulses arise at the trailing edge of the profile of the normal radio emission. Analysis of the distribution of the degree of circular polarization for the giant pulses suggests that they can consist of a random mixture of nanopulses with 100% circular polarization of either sign, with, on average, hundreds of such nanopulses within a single giant pulse.

Limits on Turbulent HiFluctuations toward PSR B0329+54 on Scales between 0.0025 and 12.5 AU

We have measured the HI absorption towards pulsar B0329+54 using the Green Bank Telescope during 18 epochs between 2002 June 30 and 2003 October 10. Three observing epochs consisted of a continuous period of 20 hours each, while fifteen epochs were 1-2 hours each. We calculate the structure function of HI absorption variations toward the pulsar on time scales of 10 minutes to 16 months which, using the proper motion of 95 km/s and the parallactic distance of 1.03 kpc measured towards B0329+54 (Brisken et al. 2002), corresponds to angular scales of 0.37 micro-arcseconds to 23.8 milli-arseconds and samples structures between 0.0025-12.5 AU assuming HI gas half way to the pulsar and ignoring scintillation effects. We find no evidence for any turbulent HI absorption fluctuations towards B0329+54, with the following upper limits on the change in opacity for various absorption features: 0.026 at -31, -21, -18, and +4 km/s, 0.12 at -11 km/s, and 0.055 at -1 km/s.

Reversals of Radio Emission Direction in PSR B1822-09

The pulse profile of pulsar B1822-09 exhibits a very peculiar kind of mode changing: a appearing just in front of the main pulse (MP) exhibits periods of nulling, during which an interpulse (IP) becomes detectable at a rotation phase separated by roughly 180° from the precursor. We propose that this bizarre phenomenon, which requires an information transfer between the two components, occurs by means of a reversal of the direction of coherent radio emission generated in the same emission region. This interpretation naturally explains the lack of weak radio emission in the off-pulse regions, as well as the problem of information transfer between emission regions associated with the MP precursor and the IP. The reversals also imply nulling. The model has profound physical implications: (1) the mechanism of coherent radio emission must allow radiation into two, opposite, intermittently changing directions; and (2) the radio waves must be able to propagate through inner regions of the neutron star magnetosphere with strong magnetic field. Most importantly, the model implies inward radio emission in the pulsar magnetosphere.

Two-frequency timing of the pulsar B1937+21 in Kalyazin and Kashima in 1997–2002

We present the results from our timing of the millisecond pulsar B1937+21, performed jointly since 1997 on two radio telescopes: the RT-64 in Kalyazin (Russia) at a frequency of 0.6GHz and RT-34 in Kashima (Japan) at a frequency of 2.15 GHz. The rms value of the pulse time of arrival (TOA) residuals for the pulsar at the barycenter of the Solar system is 1.8 μs (the relative variation is ≈10−14 over the observing period). The TOA residuals are shown to be dominated by white phase noise, which allows this pulsar to be used as an independent time scale keeper. The upper limit for the gravitational background energy density Ωg h 2 at frequencies ≈6.5 × 10−9 Hz is estimated to be no higher than 10−6. Based on the long-term timing of the pulsar, we have improved its parameters and accurately determined the dispersion measure and its time variation over the period 1984–2002, which was, on average, −0.00114(3) pc cm−3 yr−1.

Giant Pulses from PSR B1937+21 with Widths ≤15 Nanoseconds and \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $T_{b}\geq 5\times 10^{39}$ \end{document} K, the Highest Brightness Temperature Observed in the Universe

Giant radio pulses of the millisecond pulsar B1937+21 were recorded with the S2 VLBI system at 1.65 GHz with NASA/JPL's 70 m radio telescope at Tidbinbilla, Australia. These pulses have been observed as strong as 65,000 Jy with widths ≤15 ns, corresponding to a brightness temperature of Tb ≥ 5 × 1039 K, the highest observed in the universe. The vast majority of these pulses occur in 5.8 and 8.2 μs windows at the very trailing edges of the regular main pulse and interpulse profiles, respectively. Giant pulses occur, in general, with a single spike. Only in one case of 309 was the structure clearly more complex. The cumulative distribution is fitted by a power law with index -1.40 ± 0.01 with a low-energy but no high-energy cutoff. We estimate that giant pulses occur frequently but are only rarely detected. When corrected for the directivity factor, 25 giant pulses are estimated to be generated in one neutron star revolution alone. The intensities of the giant pulses of the main pulses and interpulses are not correlated with each other nor with the intensities or energies of the main pulses and interpulses themselves. Their radiation energy density can exceed 300 times the plasma energy density at the surface of the neutron star and can even exceed the magnetic field energy density at that surface. We therefore do not think that the generation of giant pulses is linked to the plasma mechanisms in the magnetosphere. Instead we suggest that it is directly related to discharges in the polar cap region of the pulsar.

X‐Ray Emission from the Old Pulsar B0950+08

We present the timing and spectral analyses of the XMM-Newton data on the 17 Myr old, nearby radio pulsar B0950+08. This observation revealed pulsations of the X-ray flux of PSR B0950+08 at its radio period, P ’ 253 ms. The pulse shape and pulsed fraction are apparently different at lower and higher energies of the observed 0.2‐10 keVenergy range, which suggests that the radiation cannot be explained by a single emission mechanism. The X-ray spectrum of the pulsar can be fitted with a power-law model with a photon index ¼1:75 � 0:15 and an (isotropic) luminosity LX ¼ (9:8 � 0:2) ; 10 29 ergs s � 1 in the 0.2‐10 keV range. Better fits are obtained with two-component, power-law plus thermal models with ¼1:30 � 0:10 and LX ¼ (9:7 � 0:1) ;10 29 ergs s � 1 for the power-law component, which presumably originates from the pulsar’s magnetosphere. The thermal component, dominating at EP0:7 keV, can be interpreted as radiation from heated polar caps on the neutron star surface covered with a hydrogen atmosphere. The inferred effective temperature, radius, and bolometric luminosity of the polar caps are TPC � 1M K,RPC � 250 m, and LPC � 3 ;1029 ergs s � 1 . Optical through X-ray nonthermal spectrum of the pulsar can be described as a single power law with ¼1:3 1:4 for the two-component X-ray fit. The ratio of the nonthermal X-ray (1‐10 keV) luminosity to the nonthermal optical (4000‐9000 8) luminosity, � 360, is within the range of 10 2 103 observed for younger pulsars, which suggests that the magnetospheric X-ray and optical emissions are powered by the same mechanism in all pulsars, independent of age and spin-down power. Assuming a standard neutron star radius, the upper limit on the temperature of the bulk of the neutron star surface, inferred from the optical and X-ray data, is about 0.15 MK. We also analyze X-ray observations of several other old pulsars, B2224+65, J2043+2740, B0628� 28, B1813� 36, B1929+10, and B0823+26, and compare their properties with those of PSR B0950+08.

Indirect Evidence of an Active Radio Pulsar in the Quiescent State of the Transient Millisecond Pulsar SAX J1808.4-3658

Millisecond radio pulsars are neutron stars that have been spun up by the transfer of angular momentum during the low-mass X-ray binary phase. The transition from an accretion-powered pulsar to a rotation-powered pulsar takes place on evolutionary timescales at the end of the accretion process; however, it may also occur sporadically in systems undergoing transient X-ray activity. We have obtained the first optical spectrum of the low-mass transient X-ray pulsar SAX J1808.4-3658 in quiescence. Similar to the black widow millisecond pulsar B1957+20, this X-ray pulsar shows a large optical modulation at the orbital period due to an irradiated companion star. Using the brightness of the companion star as a bolometer, we conclude that a very high irradiating luminosity, a factor of ~100 larger than directly observed, must be present in the system. This most likely derives from a rotation-powered neutron star that resumes activity during quiescence.

Cosmic rays and the Monogem supernova remnant

Recent findings indicate that the Monogem Ring and the associated pulsar PSR B0656 + 14 may be the `Single Source' responsible for the formation of the sharp knee in the cosmic ray energy spectrum at ∼3 PeV. The energy spectrum of cosmic rays expected for the Monogem Ring supernova remnant (SNR) from our SNR acceleration model [J. Phys. G: Nucl. Part. Phys. 27 (2001) 941] has been published by us elsewhere [J. Phys. G: Nucl. Part. Phys. 29 (2003) 709] . In this paper we go on to estimate the contribution of the pulsar B0656 + 14 to the cosmic rays in the PeV region. We conclude that although the pulsar can contribute to the formation of the knee, it cannot be the dominant source of it and an SNR is still needed. We also examine the possibility of the pulsar giving the peak of the extensive air shower (EAS) intensity observed from the region inside the Monogem Ring [ApJ Lett. 597 (2003) L129]. The estimates of the gamma-ray flux produced by cosmic ray particles from this pulsar indicate that it can be the source of the observed peak, if the particles were confined within the SNR during a considerable fraction of its total age. The flux of gamma quanta at PeV energies has a high sensitivity to the duration of the confinement. The estimates of this time and of the following diffusion of cosmic rays from the confinement volume turn out to be in remarkable agreement with the time needed for these cosmic rays to propagate to the solar system and to form the observed knee in the cosmic ray energy spectrum. Other possible mechanisms for the production of particles which could give rise to the observed narrow peak in the EAS intensity were also examined. Electrons scattered on the microwave background or on X-rays, emitted by SNR, cannot be responsible for the gamma-quanta in the peak. Neutrons produced in PP-collisions or released from the disintegration of accelerated nuclei seem to be also unable to create the peak since they cannot give the observed flux. If the experimental EAS results concerning a point-like source are confirmed, they can be important, since (i) they will give evidence for the acceleration of protons or heavier nuclei by the pulsar; (ii) they will give evidence for the existence of a confinement mechanism in SNR; (iii) they will confirm that cosmic rays produced by the Monogem Ring SNR and associated pulsar B0656 + 14 were released recently giving rise to the formation of the sharp knee and the observed narrow peak in the EAS intensity; (iv) they will give strong support for the Monogem Ring SNR and the associated pulsar B0656 + 14 being identified as the Single Source proposed in our Single Source Model of the knee. A number of predictions of the examined mechanism are made.

Pulsar Parallaxes at 5 GHz with the Very Long Baseline Array

We present the first pulsar parallaxes measured with phase-referenced pulsar VLBI observations at 5 GHz. Because of the steep spectra of pulsars, previous astrometric measurements have been at lower frequencies. However, the strongest pulsars can be observed at 5 GHz, offering the benefit of lower combined ionospheric and tropospheric phase errors, which usually limit VLBI astrometric accuracy. The pulsars B0329+54, B0355+54, and B1929+10 were observed for seven epochs spread evenly over 2 years. For B0329+54, large systematic errors led to only an upper limit on the parallax (π < 1.5 mas). A new proper motion and parallax were measured for B0355+54 (π = 0.91 ± 0.16 mas), implying a distance of 1.04 kpc and a transverse velocity of 61 km s-1. The parallax and proper motion for B1929+10 were significantly improved (π = 2.77 ± 0.07 mas), yielding a distance of 361 pc and a transverse velocity of 177 km s-1. We demonstrate that the astrometric errors are correlated with the angular separation between the phase-reference calibrator and the target source, with significantly lower errors at 5 GHz as compared to 1.6 GHz. Finally, based on our new distance determinations for B1929+10 and B0355+54, we derive or constrain the luminosities of each pulsar at high energies. We show that, for thermal emission models, the emitting area for X-rays from PSR B1929+10 is roughly consistent with the canonical size for a heated polar cap and that the conversion of spin-down power to γ-ray luminosity in B0355+54 must be low. The new proper motion for B1929+10 also implies that its progenitor is unlikely to have been the binary companion of the runaway O star ζ Ophiuchi.

Polarization observations of giant radio pulses from the millisecond pulsar B1937+21 at a frequency of 600 MHz

We performed polarization observations of giant radio pulses from the millisecond pulsar B1937+21. The observations were carried out in July 2002 with the 64-m Kalyazin radio telescope at a frequency of 600 MHz in two polarization channels with left-and right-hand circular polarizations (RCP and LCP). We used the S2 data acquisition system with a time resolution of 125 ns. The duration of an observing session was 20 min. We detected twelve giant radio pulses with peak flux densities higher than 1000 Jy; five and seven of these pulses appeared in the RCP and LCP channels, respectively. We found no event that exceeded the established detection threshold simultaneously in the two polarization channels. Thus, we may conclude that the detected giant pulses have a high degree of circular polarization, with the frequency of occurrence of RCP and LCP pulses being the same.

Timing of Binary Pulsars at Kalyazin, Russia

Regular high-precision timing of the binary pulsars J0613−0200, J1012+5307, J1022+1001, J1640+2224, J1643−1224, J1713+0747, J2145−0750 and the pulsar B1937+21 has been conducted at the Kalyazin (Russia) radio telescope RT-64 at 0.6 GHz over more than 6 years. Several of the pulsars monitored have been found to be good probes for gravitational wave background (GWB) tests, while others, having a shorter orbital period, can be used for establishing a dynamical binary pulsar timescale. Upper limits for the GWB energy density were estimated.