Proper-Motion Measurements of Pulsar B1951+32 in the Supernova Remnant CTB 80

Abstract

Using the Very Large Array and the Pie Town antenna, we have measured the position of the radio pulsar B1951+32 relative to nearby background radio sources at four epochs between 1989 and 2000. These data show a clear motion for the pulsar of 25+/-4 mas yr -1 at a position angle 252 deg +/-7 deg (north through east), corresponding to a transverse velocity 240+/-40 km s -1 for a distance to the source of 2 kpc. The measured direction of motion confirms that the pulsar is moving away from the center of its associated supernova remnant, the first time that such a result has been demonstrated. Independent of assumptions made about the pulsar birthplace, we show that the measured proper motion implies an age for the pulsar of 64+/-18 kyr, somewhat less than its characteristic age of 107 kyr. This discrepancy can be explained if the initial spin period of the pulsar was P 0 =27+/-6 ms.