A fast pulsar candidate in the globular cluster M28

Abstract

Hamilton, Helfand and Becker1 (hereafter termed HHB) have recently used the Very Large Array (VLA) telescope at 1,465 MHz to observe radio sources in globular clusters. These observations were primarily motivated by the suggestion2 that millisecond pulsar progenitors could be identified with low-mass X-ray binaries (LMXBs), and the fact that the frequency of occurrence of LMXBs per unit mass of stars is ∼100 times greater in the cores of globular clusters than in the field. HHB found a source within the core of M28, which we have observed at 30.9 and 57.5 MHz using the Clark Lake TPT synthesis telescope3. Our observations show that this source has a spectral index of −2.44. Only pulsars have well-documented spectra which are as steep as this.