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Recurrent nova M31N 2008-12a: Swift XRT observes the end of the 2015 supersoft X-ray phase

ATel #8062; M. Henze (IEEC/CSIC), M. J. Darnley (LJMU), A. W. Shafter (SDSU), M. Kato (Keio University), I. Hachisu (U. Tokyo), M. F. Bode (LJMU), J.-U. Ness (ESA/ESAC), J. P. Osborne (U. Leicester), J. A. Kennea (PSU), N. Gehrels (NASA/GSFC), for a larger collaboration
on 17 Sep 2015; 15:58 UT
Credential Certification: Martin Henze (henze@ice.cat)

Subjects: X-ray, Nova, Transient

Referred to by ATel #: 9907, 10040

In ATel #7964 we announced the discovery of the 2015 eruption of the recurrent nova M31N 2008-12a on 2015-08-28.55 UT. Comprehensive multi-wavelength studies of previous eruptions were published by Darnley et al. 2014, 2015, and Henze et al. 2014, 2015a. For additional information on the 2015 eruption see ATels #7965, #7967, #7968, #7969, #7974, #7976, #7979, #7980, #7984, #8029, #8033, and #8038. This is the 8th outburst of M31N 2008-12a in 8 consecutive years (Henze et al. 2015b).

Here we report the end of the 2015 supersoft X-ray source (SSS) phase of M31N 2008-12a around September 15. We first observed X-ray emission from the 2015 eruption on 2015-09-03.059 UT (ATel #7980).

After being last detected with (6.5±3.2) × 10-3 ct/s in a 0.9-ks Swift XRT observation on 2015-09-14.42 UT, the source had disappeared in a subsequent 5.4-ks set of observations centered on 2015-09-15.82 UT. We estimated a 3σ upper limit of 3.2 × 10-3 ct/s. The SSS phase ended about 18 days after the optical discovery which is consistent with the X-ray light curves obtained following the 2013 and 2014 eruptions (Henze et al. 2014, 2015a). Overall, the X-ray flux and effective temperature evolution mirror closely the findings presented in Henze et al. (2015a). All results are preliminary. A detailed analysis is in preparation.

We wish to thank the Swift Science Operations Team for making these observations possible, in particular the duty scientists and the science planners.