1. Supersoft and quasi-soft X-ray sources in the core of M31 Marina Orio, INAF-Torino and University of Wisconsin (2005 preprint on supersoft X-ray sources in M31)

2. The lower limit on the X-ray luminosity is 10**(34) -10**(35) erg/s in the existing Chandra and XMM-Newton images: too much for quiescent LMXB, but well below outburst luminosity. => Only a handful of GC sources. However… no “background limited” exposures of M31 have been done or will be done soon.

3. The 2x2 arcminute square of the inner core of M31: extreme crowding => excellent spatial resolution is absolutely necessary: 15% of the core X-ray sources in ~1.7% space of inner core. HOW WOULD A GC AT 15 TIMES LARGER D LOOK when observed with Chandra? XMM-MOS ACIS-S

4. In 6 arcmin**2, most of the sources outside the inner 2 arcmin square are resolved even with EPIC pn. Typical separation are > 6 arcsec.

5. The “soft” X-ray sky versus the “hard” one (1 of 4 EPIC pn images). The nature of the supersoft X-ray sources is more “easily” identified (not many choices)… Note the value of GALEX FUV images. 14x14 arcmin 14x14 arcmin, 0.2-0.6 keV14x14 arcmin, 1-10 keV

6. Identification of (all types of) X-ray sources in the inner 2x2 arcmin using other wavelengths: 2 classical novae (NOTE: they are at least 7, may be 11 among all SSS in M31): extremely luminous for 1-10 years in half of the cases 2, perhaps 4 PN 1 VERY young SNR (S And). Perhaps 2 ? 1 globular cluster source 1 LMXB 1 background AGN?

7. The XMM-Newton observations of M31 show: SNR are often “picked up” in M31 as supersoft or quasi-soft sources using Chandra-ACIS-appropriate hardness ratio criteria Post-outburst classical novae are a quarter (or a third) of the supersoft sources, but only 1 in 10 recent novae. Large, limit cycle type X-ray flux variations are only seen in ~20% of the sources. Two transients may be “wind-limited” limit cycles. Two luminous SSS show varying L(x), often exceeding L(Edd): is it the missing link with ULX? Possibility to identify stellar black holes from X-ray and optical history (using nova surveys) QSS may be a mixture of low luminosity LMXB and SNR… are perhaps foreground neutron stars also included?