Discovery of a new transient X-ray pulsar in the Small Magellanic Cloud

Abstract

Systematic Rossi X-Ray Timing Explorer (RXTE) observations of the Small Magellanic Cloud (SMC) have revealed a previously unknown transient X-ray pulsar with a pulse period of 95s. The 95s pulsar, provisionally designated XTE SMC95, was detected in three Proportional Counter Array (PCA) observations during an outburst spanning 4 weeks in March/April 1999. The pulse profile is double peaked reaching a pulse fraction of ≈ 0.8. The X-ray spectrum is well represented by an absorbed power-law with a photon index of 1.4 and mean unabsorbed flux of $\ga$8.95$\times 10^{-11}$ ergs cm -2 s -1 (3–25 keV). The source is proposed as a Be/neutron star system on the basis of its pulsations, transient nature and characteristically hard X-ray spectrum. The 2–10 keV X-ray luminosity implied by our observations is $\ga$2$\times$10 37 ergs s -1 which is consistent with that of normal outbursts seen in Galactic systems. This discovery adds to the emerging picture of the SMC as containing an extremely dense population of transient high mass X-ray binaries.