A search for radio pulsars in globular clusters, supernova remnants and transient X-ray sources

Abstract

We present the results of a targeted search for radio pulsars in globular clusters, supernova remnants (SNRs) and transient X-ray sources. 85 globular clusters, 29 SNRs and three transient X-ray sources were observed in the course of the search, during which four pulsars were found. For each object searched, the sensitivity limit is given. The four new pulsars discovered were all in globular clusters, namely PSR B1620-26 in M4, PSR B17l8-l9 in NGC6342, and PSR B1820-30A and B1820-30B in NGC6624. While PSR B1620-26 provides strong support for the binary evolution hypothesis for the formation of millisecond pulsars, PSR B17l8-l9 and B1820-30A are somewhat anomalous as they are apparently relatively young, the former pulsar and PSR B1820-30B have high magnetic fields, and all are located in old globular clusters (ages ,10 10 yr). Not surprisingly, the well-known pulsar PSR B0531 + 21 was detected in the Crab nebula SNR. The number of pulsars detected was probably limited by the finite size of pulsar emission beams, as in any survey. Other factors such as large distance, low pulsar luminosity and orbital motion may have inhibited the detection of other pulsars in globular clusters. Pulsars in SNRs and transient X -ray sources are probably less affected by these factors. Our inability to detect the former is probably due to the relatively high level of emission from the SNRs, the limited area that we observed within each target and possibly the high birth velocity of pulsars which carries them away from the centres of their remnants. Processes concerning the accretion discs of transient X -ray sources probably thwarted the detection of any potential radio pulsars in these systems.