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

ATel #6604; M. Henze (ESA/ESAC), J.-U. Ness (ESA/ESAC), M. J. Darnley (LJMU), S. C. Williams (LJMU), M. F. Bode (LJMU), A. W. Shafter (SDSU), R. A. Hounsell (STSCI)
on 22 Oct 2014; 12:52 UT
Credential Certification: Martin Henze (martin.henze@sciops.esa.int)

Subjects: X-ray, Nova, Transient

Referred to by ATel #: 9907, 10040

We report the end of the supersoft X-ray source (SSS) phase following the recent outburst of the remarkable recurrent nova M31N 2008-12a (ATel #6527). We first detected X-ray emission from this outburst on 2014-10-08.29 UT (ATel #6558) and confirmed the SSS nature of the source in ATel #6565.

After being last detected with (3.6±1.1) × 10-3 ct/s in a 4.7 ks Swift XRT observation on 2014-10-20.03 UT, the source disappeared in the following 5.8 ks observation on 2014-10-21.42 UT. We estimated a 3σ upper limit of 2.7 × 10-3 ct/s. The SSS phase ended about 18.5 days after the optical outburst, which is consistent with the X-ray light curve following the 2013 outburst (Henze et al. 2014). Overall, the X-ray properties of the 2013 and 2014 outbursts are very similar (high effective temperature, short SSS phase). A detailed analysis is in preparation.

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.