VLBI-derived Trigonometric Parallax and Proper Motion of PSR B2021+51

Abstract
We present the first results from a long-term program to measure the trigonometric parallaxes and proper motions of a set of pulsars using VLBI. We obtained these results for PSR B2021+51 from four sessions of S-band observations of the pulsar and associated reference sources. We estimate a parallax of 0.95 ± 0.37 mas, a proper motion of μα = -8.11 ± 0.24 mas yr-1 and μδ = +13.41 ± 0.25 mas yr-1, and a position at epoch 1992.723 of α = 20h22m4987031 ± 000004 and δ = 51°54'502913 ± 00003 (all J2000). Our parallax estimate implies an average electron density of 0.021 ± 0.008 cm-3 along the line of sight to the pulsar. We also effectively rule out a physical association with the supernova remnant HB 21.