Showing papers by "Richard Dodson published in 2003"

The Vela Pulsar’s Proper Motion and Parallax Derived from VLBI Observations

Abstract: The Vela pulsar is the brightest pulsar at radio wavelengths. It was the object that told us (via its glitching) that pulsars were solid rotating bodies not oscillating ones. Along with the Crab pulsar, is it the source of many of the models of pulsar behavior. Therefore it is of vital importance to know how far away it is and its origin. The proper motion and parallax for the Vela pulsar have been derived from 2.3 and 8.4 GHz very long baseline interferometry (VLBI) observations. The data span 6.8 years and consist of 11 epochs. We find a proper motion of μα cos δ = -49.68 ± 0.06, μδ = 29.9 ± 0.1 mas yr-1 and a parallax of 3.5 ± 0.2 mas, which is equivalent to a distance of 287 pc. When we subtract out the Galactic rotation and solar peculiar velocity, we find μ* = 45 ± 1.3 mas yr-1 with a position angle of 301° ± 18 which implies that the proper motion has a small but significant offset from the X-ray nebula's symmetry axis.

The radio nebula surrounding the Vela pulsar

Abstract: We have discovered that the radio nebula surrounding the Vela pulsar covers a much wider extent than previously reported, with two lobes to the north and south of the pulsar. Indications of this object have been reported previously, but its symmetric morphology around the pulsar and other details had not been identified as they were hidden due to poor sensitivity to low spatial frequencies. The structure is highly polarized and the polarization vectors, once corrected for Faraday rotation, reveal symmetry with respect to the spin axis of the pulsar. The X-ray emission found by Chandra lies at the centre of this structure, in a region that has no detectable excess of radio emission. We estimate total fluxes and regional fluxes from the northern and southern lobes, plus the X-ray region at four radio frequencies: 1.4, 2.4, 5 and 8.5 GHz. We present the corresponding images in both the total and polarized intensities, as well as those showing the derotated linear polarization vectors.

The Vela Pulsar's Radio Nebula

Abstract: We have discovered that the radio nebula surrounding the Vela pulsar covers a much wider extent than previously reported, with two lobes to the North and South of the pulsar. Indications of this object have been reported previously, but its symmetric morphology around the pulsar and other details had not been identified as they were hidden due to poor sensitivity to low spatial frequencies. The structure is highly polarised and the polarisation vectors, once corrected for Faraday rotation, reveal symmetry with respect to the spin axis of the pulsar. The X-ray emission found by Chandra lies at the centre of this structure, in a region which has no detectable excess of radio emission. We estimate total fluxes and regional fluxes from the Northern and Southern lobes, plus the X-ray region at four radio frequencies; 1.4, 2.4, 5 and 8.5 GHz. We present the corresponding images in both the total and polarised intensities, as well as those showing the derotated linear polarisation vectors.

The Vela Pulsar's proper motion and parallax derived from VLBI observations

Abstract: The Vela pulsar is the brightest pulsar at radio wavelengths. It was the object that told us (via its glitching) that pulsars were solid rotating bodies not oscillating ones. Along with the Crab pulsar is it the source of many of the models of pulsar behavior. Therefore it is of vital importance to know how far away it is, and its origin. The proper motion and parallax for the Vela pulsar have been derived from 2.3 and 8.4 GHz Very Long Baseline Interferometry (VLBI) observations. The data spans 6.8 years and consists of eleven epochs. We find a proper motion of $\mu_{\alpha {\rm cos}\delta}= -49.61 \pm 0.06, \mu_\delta= 29.8 \pm 0.1$ \myr and a parallax of $3.4 \pm 0.2$ mas, which is equivalent to a distance of $293_{-17}^{+19}$ pc. When we subtract out the galactic rotation and solar peculiar velocity we find $\mu_* = 45 \pm 1.3$ \myr with a position angle (PA) of $301^\circ\pm1.8$ which implies that the proper motion has a small but significant offset from the X-ray nebula's symmetry axis.

Pulsar Observations at Mt. Pleasant

Abstract: Two daily pulsar monitoring programs are progressing at the Mount Pleasant Observatory, Hobart, Tasmania, Australia. A new system involving the 26-metre radio telescope monitors 10 young pulsars daily and is focussed on near-real-time glitch finding. This will allow Target of Opportunity observations to measure post-glitch heating of the neutron star surface (Helfand, Gotthelf, & Halpern 2000). The 14-metre continues its 21st year of daily monitoring of the Vela pulsar with a recent comprehensive frontend upgrade. This is prior to an upgrade of the backend equipment currently in progress. The 14-metre observed the most recent glitch of the Vela pulsar in January 2000 to the highest time resolution of any glitch and revealed a particularly short-term decay component (Dodson, McCulloch, & Lewis 2002). This decay component will provide constraints to the nature of the coupling of the stellar crust to the liquid interior.