Sub-Milliarcsecond Precision of Pulsar Motions: Using In-Beam Calibrators with the VLBA

Abstract

We present Very Long Baseline Array (VLBA) phase-referenced measurements of the parallax and proper motion of two pulsars, B0919+06 and B1857-26. Sub-milliarcsecond positional accuracy was obtained by simultaneously observing a weak calibrator source within the 40' field of view of the VLBA at 1.5 GHz. We discuss the merits of using weak close calibrator sources for Very Long Baseline Interferometry (VLBI) observations at low frequencies, and we outline a method of observation and data reduction for these type of measurements. For the pulsar B0919+06 we measure a parallax of 0.31 ± 0.14 mas. The accuracy of the proper motions is ≈0.5 mas yr^-1, an order of magnitude improvement over most previous determinations.