Discovery of a Peculiar Pulsar in the Small Magellanic Cloud

We report on a peculiar X-ray binary pulsar, IKT 1 = RX J0047.3−7312, observed with XMM-Newton in 2000 October. The X-ray spectrum is described by a two-component spectrum. The hard component has a broken power-law with respective photon indices of 0.2 and 1.8, below and above the break energy at 5.8keV. The soft component can be modeled by a blackbody of kT =0 .6keV. The X-ray flux shows a gradual decrease and periodic variations of about 4000s. The averaged flux in 0.7–10.0keV is 2.9 × 10 −12 ergcm −2 s −1 ,w hich is∼ 10-times brighter than that in a ROSAT observation in 1999 November. In addition to the 4000-s variation, we found coherent pulsations of 263 ±1s. These discoveries strengthen the Be/X-ray binary scenario proposed by the ROSAT and ASCA observations on this source, and confirm that most of the hard sources in the Small Magellanic Cloud are X-ray binary pulsars. A peculiar property of this XBP is that the coherent pulsations are found only in the soft component, and the folded light curve shows a flat top shape with a sharp dip. We discuss the nature of this XBP focusing on the peculiar soft component.