PRECISION ASTROMETRY WITH THE VERY LONG BASELINE ARRAY: PARALLAXES AND PROPER MOTIONS FOR 14 PULSARS

Abstract

Astrometry can bring powerful constraints to bear on a variety of scientific\nquestions about neutron stars, including their origins, astrophysics,\nevolution, and environments. Using phase-referenced observations at the VLBA,\nin conjunction with pulsar gating and in-beam calibration, we have measured the\nparallaxes and proper motions for 14 pulsars. The smallest measured parallax in\nour sample is 0.13+-0.02 mas for PSR B1541+09, which has a most probable\ndistance of 7.2+1.3-1.1 kpc. We detail our methods, including initial VLA\nsurveys to select candidates and find in-beam calibrators, VLBA\nphase-referencing, pulsar gating, calibration, and data reduction. The use of\nthe bootstrap method to estimate astrometric uncertainties in the presence of\nunmodeled systematic errors is also described. Based on our new\nmodel-independent estimates for distance and transverse velocity, we\ninvestigate the kinematics and birth sites of the pulsars and revisit models of\nthe Galactic electron density distribution. We find that young pulsars are\nmoving away from the Galactic plane, as expected, and that age estimates from\nkinematics and pulsar spindown are generally in agreement, with certain notable\nexceptions. Given its present trajectory, the pulsar B2045-16 was plausibly\nborn in the open cluster NGC 6604. For several high-latitude pulsars, the\nNE2001 electron density model underestimates the parallax distances by a factor\nof two, while in others the estimates agree with or are larger than the\nparallax distances, suggesting that the interstellar medium is irregular on\nrelevant length scales. The VLBA astrometric results for the recycled pulsar\nJ1713+0747 are consistent with two independent estimates from pulse timing,\nenabling a consistency check between the different reference frames.\n