Discovery of Pulsed X-Rays from the SMC Transient RX J0052.1–7319

Coherent 65 mHz pulsations in the X-ray flux of the Small Magellanic Cloud (SMC) transient source RX J0052.1-7319 have been detected by us in an analysis of ROSAT data. We report on the pulsations we detected in ROSAT HRI data and simultaneous detection of these pulses in hard X-rays using BATSE data. The BATSE data show an outburst of the source lasting 60 days. We report on optical observations of the candidate companion, and a new source position we determined from the HRI data, which is consistent with the candidate's location. From the measured fluxes and observed frequency derivatives we exclude the possibility that the pulsar is in the foreground of the SMC and show that an accretion disk is present during the outburst, which peaked near Eddington luminosity.