PSR B1745−20 and Young Pulsars in Globular Clusters

Abstract

Recent searches for radio pulsars in globular clusters have targeted the millisecond pulsars (MSPs) that are expected to result from the spin-up of old neutron stars in low-mass X-ray binary systems. These surveys have been very successful, discovering 34 pulsars, most of which are old and probably recycled by accretion-powered spin-up in a binary system. However, three objects have properties that are more like those of the normal population of Galactic pulsars. Timing measurements of one such pulsar, PSR B1745-20, show that it is clearly associated with the cluster NGC 6440 and that it is solitary and young, with a large magnetic field. This pulsar, together with PSR B1820-30B in NGC 6624, establishes long-period pulsars associated with globular clusters as a distinct group that seems to have a completely different genesis to the MSP population in globular clusters. Produced at a comparable rate to the MSPs, the origin of such apparently young objects in very old stellar systems is not understood.