BeppoSAX and Chandra observations of SAX J0103.2-7209=2E 0101.5-7225:: A new persistent 345 second X-ray pulsar in the small magellanic cloud

We report the results of a 1998 July BeppoSAX observation of a field in the Small Magellanic Cloud which led to the discovery of similar to 345 s pulsations in the X-ray flux of SAX J0103.2-7209. The BeppoSAX X-ray spectrum is well fitted by an absorbed power law with a photon index of similar to 1.0 plus a blackbody component with kT = 0.11 keV. The unabsorbed luminosity in the 2-10 keV energy range is similar to 1.2 x 10(36) ergs s(-1). In a very recent Chandra observation, the 345 s pulsations are also detected. The available period measurements provide a constant period derivative of -1.7 s yr(-1) over the last 3 years, making SAX J0103.2-7209 one of the most rapidly spinning up X-ray pulsars known. The BeppoSAX position (30 " uncertainty radius) is consistent with that of the Einstein source 2E 0101.5-7225 and the ROSAT source RX J0103.2-7209. This source was detected at a luminosity level of a few times 10(35)-10(36) ergs s(-1) in all data sets of past X-ray missions since 1979. The ROSAT HRI and Chandra positions are consistent with that of a m(v) = 14.8 Be spectral-type star already proposed as the likely optical counterpart of 2E 0101.5-7225. We briefly report and discuss photometric and spectroscopic data carried out at the ESO telescopes 2 days before the BeppoSAX observation. We conclude that SAX J0103.2-7209 and 2E 0101.5-7225 are the same source: a relatively young and persistent X-ray pulsar in the SMC.