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Supersoft X-ray sources in M31

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.

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Supersoft X-ray sources in M31

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

  2. Supersoft X-ray sources in M31: everywhere

  3. 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)

  4. 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)

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

  6. 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

  7. 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

  8. 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

  9. 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.

  10. A distinct population of younger SSS

  11. 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

  12. 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).

  13. 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)

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