Pulsar Parallaxes at 5 GHz with the Very Long Baseline Array

Abstract

We present the first pulsar parallaxes measured with phase-referenced pulsar\nVLBI observations at 5 GHz. Due to the steep spectra of pulsars, previous\nastrometric measurements have been at lower frequencies. However, the strongest\npulsars can be observed at 5 GHz, offering the benefit of lower combined\nionospheric and tropospheric phase errors, which usually limit VLBI astrometric\naccuracy. The pulsars B0329+54, B0355+54 and B1929+10 were observed for 7\nepochs spread evenly over 2 years. For B0329+54, large systematic errors lead\nto only an upper limit on the parallax (pi < 1.5 mas). A new proper motion and\nparallax were measured for B0355+54 (pi = 0.91 +- 0.16 mas), implying a\ndistance of 1.04+0.21-0.16 kpc and a transverse velocity of 61+12-9 km/s. The\nparallax and proper motion for B1929+10 were significantly improved (pi = 2.77\n+- 0.07 mas), yielding a distance of 361+10-8 pc and a transverse velocity of\n177+4-5 km/s. We demonstrate that the astrometric errors are correlated with\nthe angular separation between the phase reference calibrator and the target\nsource, with significantly lower errors at 5 GHz compared to 1.6 GHz. Finally,\nbased on our new distance determinations for B1929+10 and B0355+54, we derive\nor constrain the luminosities of each pulsar at high energies. We show that,\nfor thermal emission models, the emitting area for X-rays from PSR B1929+10 is\nroughly consistent with the canonical size for a heated polar cap, and that the\nconversion of spin-down power to gamma-ray luminosity in B0355+54 must be low.\nThe new proper motion for B1929+10 also implies that its progenitor is unlikely\nto have been the binary companion of the runaway O-star zeta-Ophiuchi.\n