1.5 millisecond pulsar

Recent observations of the 1.5-msec pulsar in the field of 4C21.53 are summarized and discussed. Its nondetection in earlier pulsar searches is attributed to insufficient search range. It is inferred from the rotational energy of the pulsar and the lack of supernova debris in its vicinity that it has an age of at least 1 Myr, and a low magnetic moment, and that it was created either ab initio with low magnetic moment or by spin-up from a binary, with the secondary forming a supernova. The very small spindown rate (about 10 to the -19th sec/sec) estimated from pulse arrival times suggests that the period and period decay law will remain stable. Hence the pulsar can be useful for measuring ephemeris times, gravitational redshift, and planetary masses, and (if more msec pulsars can be found) for directly determining pulsar coordinates, planetary orbits, and one post-Newtonian general-relativity parameter