Distance to the 1.5 millisecond pulsar and other 4C 21.53 objects

Abstract

The distance to the 1.5 millisecond pulsar is estimated as 5 kpc based on neutral hydrogen absorption measurements. Two nearby sources, which along with the pulsar constitute the 4C 21.53 complex of radio sources, are shown to be more distant than the pulsar. In particular, 4C 21.53 W, the H II region adjacent to the pulsar is about 10.7 kpc distant and clearly unrelated. The pulsar H I absorption measurement required development of a new observing technique which is described in detail.