Pulsar astrometry via VLBI

The feasibility of pulsar astrometry via VLBI is demonstrated, and results are reported for the positions of two pulsars in the reference frame determined by VLBI observations of compact extragalactic radio sources. The celestial coordinates of PSR 0329 + 54 and PSR 1133 + 16 are given along with their separations from distant, compact radio sources nearby in the sky with uncertainties as low as several milliarcseconds. Comparison with positions determined with the 35-km baseline interferometer and the VLA shows good agreement in both coordinates. However, comparison with positions determined via pulse-time-of-arrival measurements shows a disagreement of 4.5 sigma with Downs' and Reichley's (1983) value for the declination of PSR 0329 + 54. This discrepancy is probably caused by systematic errors not reflected in the uncertainties for pulse-timing results.