arXiv subjects

J. S. Sandhu

Publications and source records attributed to J. S. Sandhu.

6 recordsLinked to original sources

arXiv1999

Parallax of PSR J1744-1134 and the Local Interstellar Medium

We present the annual trigonometric parallax of PSR J1744-1134 derived from an analysis of pulse times of arrival. The measured parallax, pi = 2.8+/-0.3 mas ranks among the most precisely determined distances to any pulsar. The parallax distance of 357+/-39 pc is over twice that derived from the dispersion measure using the Taylor & Cordes model for the Galactic electron distribution. The mean electron density in the path to the pulsar, n_e = (0.0088 +/- 0.0009) cm^{-3}, is the lowest for any disk pulsar. We have compared the n_e for PSR J1744-1134 with those for another 11 nearby pulsars with independent distance estimates. We conclude that there is a striking asymmetry in the distribution of electrons in the local interstellar medium. The electron column densities for pulsars in the third Galactic quadrant are found to be systematically higher than for those in the first. The former correlate with the position of the well known local HI cavity in quadrant three. The excess electrons within the cavity may be in the form of HII clouds marking a region of interaction between the local hot bubble and a nearby superbubble.

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arXiv1998

Millisecond Pulsar Velocities

We present improved timing parameters for 13 millisecond pulsars (MSPs) including 9 new proper motion measurements. These new proper motions bring to 23 the number of MSPs with measured transverse velocities. In light of these new results we present and compare the kinematic properties of MSPs with those of ordinary pulsars. The mean transverse velocity of MSPs was found to be 85+/-13 km/s; a value consistent with most models for the origin and evolution of MSPs and approximately a factor of four lower than that of ordinary pulsars. We also find that, in contrast to young ordinary pulsars, the vast majority of which are moving away from the Galactic plane, almost half of the MSPs are moving towards the plane. This near isotropy would be expected of a population that has reached dynamic equilibrium. Accurate measurements of MSP velocities have allowed us to correct their measured spin-down rates for Doppler acceleration effects, and thereby derive their intrinsic magnetic field strengths and characteristic ages. We find that close to half of our sample of MSPs have a characteristic age comparable to or greater than the age of the Galaxy.

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arXiv1998

Spectra of Southern Pulsars

We compare the spectral properties of the millisecond and slow pulsars detected in the Parkes 70 cm survey. The mean spectral index for the millisecond pulsars (MSPs) is -1.9 +/- 0.1 whereas the mean spectral index for the slow pulsars is a surprisingly steep -1.72 +/- 0.04. A Kolmogorov-Smirnov test indicates that there is only a 72% probability that the two distributions differ. As a class, MSPs are therefore only fractionally steeper-spectrum objects than slow pulsars, as recent literature would suggest. We then model the expected distribution of millisecond pulsars in the Galaxy and find that high-frequency surveys, with sensitivities similar to the current Parkes multibeam survey, are likely to detect MSPs in large numbers. The observed distribution of MSPs will be much less isotropic than that resulting from low-frequency surveys, with 50% of detectable MSPs residing within 11 degrees of the Galactic plane in an all-sky survey.

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arXiv1998

The Orbital Evolution and Proper Motion of PSR J2051-0827

We have carried out high-precision timing observations of the eclipsing binary PSR J2051-0827 in the 3.3 years since its discovery. These data indicate that the orbital period is decreasing at a rate of dPb/dt = (-11+-1)X10^-12. If secular, this orbital period derivative implies a decay time for the orbit of only 25 Myr which is much shorter than the expected timescale for ablation of the companion. We have also measured the proper motion of the pulsar to be 5+-3 mas/yr. Assuming the pulsar is at the dispersion-measure distance this implies a very slow transverse velocity vt=(30+-20) km/s. This combination of low velocity and short orbital period argue against formation of the system in the standard manner and we discuss the implications for its evolutionary history.

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arXiv1997

Discovery of the Young, Energetic Radio Pulsar PSR J1105-6107

We report the discovery and follow-up timing observations of the 63 ms radio pulsar, PSR J1105-6107. The pulsar is young, having a characteristic age of only 63 kyr and, from its dispersion measure, is estimated to be at a distance of ~7 kpc from the Sun. We consider its possible association with the nearby supernova remnant G290.1-0.8 (MSH 11-61A); an association requires that the pulsar's proper motion be ~22 mas/yr (corresponding to ~650 km/s for a distance of 7 kpc) directed away from the remnant center, assuming that the characteristic age is the true age. The pulsar's spin-down luminosity, 2.5 x 10^{36} erg/s, is in the top 1% of all known pulsar spin-down luminosities. Given its estimated distance, PSR J1105-6107 is therefore likely to be observable at high energies. Indeed, it is coincident with the known CGRO/EGRET source 2EG J1103-6106; we consider the possible association and conclude that it is likely.

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arXiv1996

Timing Measurements and Their Implications for Four Binary Millisecond Pulsars

We present timing observations of four millisecond pulsars, using data obtained over three years at the ATNF Parkes and NRAL Jodrell Bank radio telescopes. Astrometric, spin, and binary parameters are updated, and substantially improved for three pulsars, PSRs J0613-0200, J1045-4509 and J1643-1224. We have measured the time variation of the projected semi-major axis of the PSR J0437-4715 orbit due to its proper motion, and use it to constrain the inclination of the orbit and the mass of the companion. Some evidence is found for changes in the dispersion measures of PSRs J1045-4509 and J1643-1224. Limits are placed on the existence of planetary mass companions, ruling out companions with masses and orbits similar to the terrestrial planets of the solar system for eight pulsars.

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