arXiv subjects

I. H. Stairs

Publications and source records attributed to I. H. Stairs.

193 records · Page 11Linked to original sources

arXiv2000

The likely detection of pulsed high-energy gamma-ray emission from millisecond pulsar PSR J0218+4232

We report circumstantial evidence for the first detection of pulsed high-energy gamma-ray emission from a millisecond pulsar, PSR J0218+4232, using data collected with the Energetic Gamma Ray Experiment (EGRET) on board the Compton Gamma Ray Observatory (CGRO). The EGRET source 3EG J0222+4253 is shown to be spatially consistent with PSR J0218+4232 for the energy range 100 - 300 MeV. Above 1 GeV the nearby BL Lac 3C 66A is the evident counterpart, and between 300 MeV and 1 GeV both sources contribute to the gamma-ray excess. Folding the 100-1000 MeV photons with an accurate radio ephemeris of PSR J0218+4232 yields a double peaked pulse profile with a ~3.5 sigma modulation significance and with a peak separation of ~0.45 similar to the 0.1-10 keV pulse profile.

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arXiv2000

Discovery of a Young Radio Pulsar in a Relativistic Binary Orbit

We report on the discovery of PSR J1141-6545, a radio pulsar in an eccentric, relativistic 5-hr binary orbit. The pulsar shows no evidence for being recycled, having pulse period P = 394 ms, characteristic age tau_c = 1.4 x 10^6 yr, and inferred surface magnetic dipole field strength B = 1.3 x 10^12 G. From the mass function and measured rate of periastron advance, we determine the total mass in the system to be (2.300 +/- 0.012) solar masses, assuming that the periastron advance is purely relativistic. Under the same assumption, we constrain the pulsar's mass to be M_p < 1.348 solar masses and the companion's mass to be M_c > 0.968 solar masses (both 99% confidence). Given the total system mass and the distribution of measured neutron star masses, the companion is probably a massive white dwarf which formed prior to the birth of the pulsar. Optical observations can test this hypothesis.

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arXiv2000

A Baseband Recorder for Radio Pulsar Observations

Digital signal recorders are becoming widely used in several subfields of centimetre-wavelength radio astronomy. We review the benefits and design considerations of such systems and describe the Princeton Mark IV instrument, an implementation designed for coherent-dedispersion pulsar observations. Features of this instrument include corrections for the distortions caused by coarse quantization of the incoming signal, as well algorithms which effectively excise both narrowband and broadband radio-frequency interference. Observations at 430 MHz using the Mark IV system in parallel with a system using a 250 kHz filter bank and incoherent dedispersion demonstrated timing precision improvement by a factor of 3 or better for typical millisecond pulsars.

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arXiv2000

Coherently Dedispersed Polarimetry of Millisecond Pulsars

We present a large sample of high-precision, coherently-dedispersed polarization profiles of millisecond pulsars (MSPs) at frequencies between 410 and 1414 MHz. These data include the first polarimetric observations of several of the pulsars, and the first low-frequency polarization profiles for others. Our observations support previous suggestions that the pulse shapes and polarimetry of MSPs are more complex than those of their slower relatives. An immediate conclusion is that polarimetry-based classification schemes proposed for young pulsars are of only limited use when applied to millisecond pulsars.

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arXiv2000

Pulse shape and spectrum of PSR J0218+4232 observed with BeppoSAX

We present the results of a BeppoSAX observation of PSR J0218+4232 which, for the first time, provides detailed information on the pulsar's temporal and spectral emission properties in the broad band 1-10 keV. We detected X-ray pulses with a pulsed fraction of 73 +/- 12 %. The pulse profile is characterized by two peaks phase separated by 0.47 +/-0.05. The pulsed spectrum is best described by a power-law of photon index 0.61 +/- 0.32 with an unabsorbed (2-10 keV) X-ray flux of 4.1E-13 erg/cm^2/s implying a luminosity of Lx = 1.3E32 Theta (d/5.7 kpc})^2 erg/s and an X-ray efficiency of 4.8E-4 Theta (d/5.7 kpc})^2 where Theta is the solid angle spanned by the emission beam.

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arXiv1999

The Parkes Multibeam Pulsar Survey: preliminary results

A high-frequency survey of the Galactic plane for radio pulsars is in progress, using the multibeam receiver on the 64-m Parkes radiotelescope. We describe the survey motivations, the observing plan and the inital results. The survey is discovering many pulsars, more than 500 so far. Eight of the new pulsars are binary, one with a massive companion. At least eight are young, with characteristic ages of less than 100 kyr. Two of these (Kaspi et al, this Conference) have surface dipole magnetic field strengths greater than any other known radio pulsar.

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arXiv1999

Geodetic Precession in PSR B1534+12

We present Arecibo observations of PSR B1534+12 which confirm previous suggestions that the pulse profile is evolving secularly. This effect is similar to that seen in PSR B1913+16, and is almost certainly due to general relativistic precession of the pulsar's spin axis.

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arXiv1999

Timing the Parkes Multibeam Pulsars

Measurement of accurate positions, pulse periods and period derivatives is an essential follow-up to any pulsar survey. The procedures being used to obtain timing parameters for the pulsars discovered in the Parkes multibeam pulsar survey are described. Completed solutions have been obtained so far for about 80 pulsars. They show that the survey is preferentially finding pulsars with higher than average surface dipole magnetic fields. Eight pulsars have been shown to be members of binary systems and some of the more interesting results relating to these are presented.

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arXiv1999

The Parkes Multibeam Pulsar Survey: PSR J1811-1736 - a pulsar in a highly eccentric binary system

We are undertaking a high-frequency survey of the Galactic plane for radio pulsars, using the 13-element multibeam receiver on the 64-m Parkes radio telescope. We describe briefly the survey system and some of the initial results. PSR J1811-1736, one of the first pulsars discovered with this system, has a rotation period of 104 ms. Subsequent timing observations using the 76-m radio telescope at Jodrell Bank show that it is in an 18.8-day, highly-eccentric binary orbit. We have measured the rate of advance of periastron which indicates a total system mass of 2.6 +- 0.9 Msun, and the minimum companion mass is about 0.7 Msun. This, the high orbital eccentricity and the recycled nature of the pulsar suggests that this system is composed of two neutron stars, only the fourth or fifth such system known in the disk of the Galaxy.

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arXiv1999

The Parkes Multibeam Pulsar Survey

The Parkes multibeam pulsar survey uses a 13-element receiver operating at a wavelength of 20 cm to survey the inner Galactic plane with remarkable sensitivity. To date we have collected and analyzed data from 45% of the survey region (|b| < 5 deg.; 260 deg. < l < 50 deg.), and have discovered 440 pulsars, in addition to re-detecting 190 previously known ones. Most of the newly discovered pulsars are at great distances, as inferred from a median dispersion measure (DM) of 400 pc/cm^3.

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arXiv1999

Recent Arecibo Timing of the Relativistic Binary PSR B1534+12

We present a new timing solution for PSR B1534+12, based on coherently-dedispersed observations at Jodrell Bank and, recently, Arecibo. The new data have resulted in improved measurements of the post-Keplerian timing parameters, including the orbital period derivative. At present, the poorly-known distance to the pulsar limits the precision of the measurement of the intrinsic orbital period derivative, and hence the strength of the test of general relativity that results from this binary system. By assuming that general relativity is the correct theory of gravity, we may invert the test and find an improved value of the pulsar distance.

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arXiv1999

The Parkes Multibeam Pulsar Survey

The Parkes multibeam pulsar survey is a high-frequency, fast-sampled survey of the Galactic Plane, expected to discover at least 500 new pulsars. To date, over 200 pulsars have been found, including several young pulsars and at least one with a very high magnetic field. Seven of the new stars are in binary systems; this number includes one probable double-neutron-star system, and one pulsar with an extremely massive companion.

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arXiv1997

Measurement of Relativistic Orbital Decay in the PSR B1534+12 Binary System

We have made timing observations of binary pulsar PSR B1534+12 with radio telescopes at Arecibo, Green Bank, and Jodrell Bank. By combining our new observations with data collected up to seven years earlier, we obtain a significantly improved solution for the astrometric, spin, and orbital parameters of the system. For the first time in any binary pulsar system, no fewer than five relativistic or "post-Keplerian" orbital parameters are measurable with useful accuracies in a theory-independent way. We find the orbital period of the system to be decreasing at a rate close to that expected from gravitational radiation damping, according to general relativity, although the precision of this test is limited to about 15% by the otherwise poorly known distance to the pulsar. The remaining post-Keplerian parameters are all consistent with one another and all but one of them have fractional accuracies better than 1%. By assuming that general relativity is the correct theory of gravity, at least to the accuracy demanded by this experiment, we find the masses of the pulsar and companion star each to be 1.339+-0.003 Msun and the system's distance to be d = 1.1+-0.2 kpc, marginally larger than the d ~ 0.7 kpc estimated from the dispersion measure. The increased distance reduces estimates of the projected rate of coalescence of double neutron-star systems in the universe, a quantity of considerable interest for experiments with terrestrial gravitational wave detectors such as LIGO.

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