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M. Orio (INAF-Torino, Italy and Univ. Wisconsin)
I examined the observations of M31 done with XMM-Newton and selected supersoft X-ray sources (SuSo) and quasi-soft-sources (QSS), using hardness criteria equivalent to the ones applied to Chandra observations, then I also studied the sources' broad band spectra. 16 SuSo were detected, of which 9 were not detected before with either Chandra or ROSAT, and 7 were observed and classified as SuSo using ROSAT and/or Chandra. Two supernova remnants, previously observed with Chandra, also have an extremely soft spectrum, that can be classified as SuSo, and the same is true for at least two objects which are almost certainly foreground stars. Several spurious sources, up to 25 probably included in compilations of extragalactic SuSo based only on hardness ratio. Of the QSS observed in M31 with Chandra, 5 out of 7 that were observed again and were always detected, while two are variable. Four SuSo are spatially coincident with classical novae that have exploded in M31 in the last 13 years. Only the spectra of these supposed-novae and of three, perhaps four more unidentified and variable sources, are approximately fitted with a blackbody or white dwarf atmospheric model at near-Eddington luminosity for the distance of M31. Some of the other spectra of SuSo and QSS may not be stellar and the X-ray fluxes are low.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.