Supersoft X-ray sources in M31 Marina Orio INAF-Padova and U Wisconsin In collaboration with Tommy Nelson

Supersoft X-ray sources in M31: everywhere

Analysis of XMM-Newton-Chandra-LGS(WIYN)-Galex archival images We examined 78 objects - a statistically significant sample (including SNR, excluding uncertain detections/mixed spectra states) 5 new SSS and 3 (not published) novae in XMM images 50of these SSS were observed more than once Searched multi-wavelength counterparts and examined the long term X-ray time variability Only 1 AGN? Less than 10% of SSS are SNR (S And not confirmed) Only 15% Cal 83/RXJ 0513 type sources Are half of M31 SSS novae? (At least 17% are) 25% of SSS associated with B-stars/star formation (Nelson’s talk)

M31 novae seem to be X-ray sources for longer. Selection effect? Probably not. Different OBSERVABLE populations. M31 MW NOTE: Novae also bright in UV, but only for 1 year (mostly due to shell emission)

Other M31 (temptative, partial Chandra HRC-I results)

Nova 2007 12-b: another RS Oph? One of the brightest sources in M31, on after 34 days, peak at 2 months, ~1100s period, disappeared completely after 6 months. Effective temperature above 800,000 K!!! It was a nova of the He/N and Fe II spectroscopic class (Shafter), typical of recurrent novae

Comparison: r2-12 vs.Nova 2007 12-b r2-12 is the brightest SSS of M31 - only possible counterparts within 2” are 2-3 red stars, R~24-25 Clear periodicity 212 s - how can it be a NS? Luminosity exceeding 1038 erg/s, variable by a factor ~few Effective T >~ 800,000 K most of the time, fainter harder tail Count rate, luminosity and spectral shape very similar to N 2007 12-b AND RS Oph at ~2 months N 2007 12-b is different because of deeper and red shifted absorption feature of N VI at ~25 AA, and superimposed emission lines, like RS Oph

Persistent - recurrent sources: Only 3 SSS (out of 50!!!) are always above the detection upper limits A few other “persistent” sources are not SSS at all… 6 more SSS have “dips” or a recurrent behaviour r1-25

r3-8 is NOT a foreground polar or neutron star Luminosity “dips” by more than an order of mag (at least 2 likely) on time scale 3<=t<6 months argues against NS: variability occurs within weeks Lack of any UV/optical counterpart with B<24, R<25 argues against foreground polar (favored by Williams et al. 2006) One of the most interesting SSS in M31 because of similarity with LMC/SMC sources Lack of bright red counterpart argue against symbiotic It is probably a sister of RX J0513.

A distinct population of younger SSS

UV band of Galex are FUV=1350-1800 AA NUV=1800-2800 AA B stars are main sources Below 200,000 K only very extended sources detectable in X

RX J040. 0 was not observed again in 2007; in SF region RX J040.0 was not observed again in 2007; in SF region. It has colors of H-burning WD. RX J0045.4 on for at last 1 year, then off, in SF region. B-star colors. RX J0042.2 is a persistent source (Nelson’s talk).

Preliminary conclusions: Only 11 out of 50 repeatedly observed sources were detected again Three sources were “permanently detected - the best known, r2-12 is periodically and aperiodically variable, with similar spectrum to a “massive WD nova” at maximum..for ~20 years 8 repeated SSS are “wildly variable” Up to a half (NOT MORE…) may be NOVAE SNR can be a contaminant A quarter of the sources (many of them transient) are… High Mass Binaries??? (Nelson)