Pulsar Parallaxes at 5 GHz with the Very Long Baseline Array

We present the first pulsar parallaxes measured with phase-referenced pulsarVLBI observations at 5 GHz. Due to the steep spectra of pulsars, previousastrometric measurements have been at lower frequencies. However, the strongestpulsars can be observed at 5 GHz, offering the benefit of lower combinedionospheric and tropospheric phase errors, which usually limit VLBI astrometricaccuracy. The pulsars B0329+54, B0355+54 and B1929+10 were observed for 7epochs spread evenly over 2 years. For B0329+54, large systematic errors leadto only an upper limit on the parallax (pi < 1.5 mas). A new proper motion andparallax were measured for B0355+54 (pi = 0.91 +- 0.16 mas), implying adistance of 1.04+0.21-0.16 kpc and a transverse velocity of 61+12-9 km/s. Theparallax and proper motion for B1929+10 were significantly improved (pi = 2.77+- 0.07 mas), yielding a distance of 361+10-8 pc and a transverse velocity of177+4-5 km/s. We demonstrate that the astrometric errors are correlated withthe angular separation between the phase reference calibrator and the targetsource, with significantly lower errors at 5 GHz compared to 1.6 GHz. Finally,based on our new distance determinations for B1929+10 and B0355+54, we deriveor 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 isroughly consistent with the canonical size for a heated polar cap, and that theconversion of spin-down power to gamma-ray luminosity in B0355+54 must be low.The new proper motion for B1929+10 also implies that its progenitor is unlikelyto have been the binary companion of the runaway O-star zeta-Ophiuchi.Comment: 8 pages, including 3 figures and 3 tables; emulateapj; ApJ submitte