The Pulsar in GRO J1744-28 at Low Flux

Abstract

The Bursting Pulsar, GRO J1744-28, has been observed with the Rossi X-ray Timing Explorer (RXTE) regularly since the launch of the satellite in December 1995. This accretion driven pulsar has undergone two outbursts which have been accompanied by significant spin-up of the pulsar. Between these two outbursts, the pulsar was detectable during each observation down to fluxes perhaps one thousandth of the persistent flux at the peak of the first outburst. We observe evidence of a change in the sign of the frequency derivative during the faintest period but the relationship between the observed luminosity and the frequency derivative is complex.