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 JulyBeppoSAXobservation of a field in the Small Magellanic Cloud whichled to the discovery ofª345 s pulsations in the X-ray flux of SAX J0103.227209. TheBeppoSAXX-ray spectrumis well fitted by an absorbed power law with a photon index ofª1.0 plus a blackbody component withkT =keV. The unabsorbed luminosity in the 2–10 keV energy range isªergs s21. In a very recent360.111.2#10Chandraobservation, the 345 s pulsations are also detected. The available period measurements provide a constantperiod derivative of21.7 s yr21over the last 3 years, making SAX J0103.227209 one of the most rapidlyspinning up X–ray pulsars known. TheBeppoSAXposition (300uncertainty radius) is consistent with that of theEinsteinsource 2E 0101.527225 and theROSATsource RX J0103.227209. This source was detected at aluminosity level of a few times 1035–1036ergs s21in all data sets of past X-ray missions since 1979. TheROSATHRI andChandrapositions are consistent with that of aBe spectral-type star already proposed as them=14.8Vlikely optical counterpart of 2E 0101.527225. We briefly report and discuss photometric and spectroscopic datacarried out at the ESO telescopes 2 days before theBeppoSAXobservation. We conclude that SAX J0103.227209and 2E 0101.527225 are the same source: a relatively young and persistent X-ray pulsar in the SMC.