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Recurrent nova M31N 1963-09c: Swift XRT detection of the 2015 eruption as a supersoft X-ray source

ATel #8290; M. Henze (IEEC/CSIC), S. C. Williams (LJMU), M. J. Darnley (LJMU), A. W. Shafter (SDSU), K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic)
on 16 Nov 2015; 16:44 UT
Credential Certification: Martin Henze (henze@ice.cat)

Subjects: X-ray, Nova, Transient

We report the beginning of the supersoft X-ray source (SSS) phase of the 2015 eruption of the recurrent nova M31N 1963-09c (see ATels #8243, #8242, #8238, #8235, #8234, #8233 and CBAT TOCP). The nova was detected as a faint X-ray source with (3±1) × 10-3 ct s-1 in an 5.6-ks Swift XRT observation obtained on 2015-11-14.07 UT. This corresponds to day 14.05 after eruption. An increased concentration of soft X-ray counts is clearly visible at the nova position. No counts were detected with a formal 3σ upper limit of 3.3 × 10-3 ct s-1 in an 3.1-ks XRT observation on 2015-11-13.14 UT (day 13.14).

The count rate and timing of the SSS turn on are consistent with the X-ray observations of the 2010 eruption (ATel #3038). The early SSS phase of M31N 1963-09c is expected to be highly variable and the full X-ray luminosity should soon emerge. We will continue to monitor the X-ray light curve of this unusual recurrent nova throughout its expected SSS phase (cf. Henze et al. 2014).

We wish to thank the Swift Team for making the ToO observations possible, in particular N. Gehrels, the duty scientists as well as the science planners.