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Recurrent nova M31N 2008-12a: The 2017-eruption X-ray turn-off seen by Swift/XRT

ATel #11214; M. Henze (SDSU), M. J. Darnley (LJMU), A. W. Shafter (SDSU), S. Kafka (AAVSO), M. Kato (Keio University), S. C. Williams (Lancaster), for a larger collaboration
on 22 Jan 2018; 18:21 UT
Credential Certification: Martin Henze (henze@ice.cat)

Subjects: X-ray, Nova, Transient

The detection of supersoft X-ray source (SSS) emission from the 2017 eruption (ATel #11116) of the rapidly recurring nova M31N 2008-12a (Henze et al. 2014, 2015a, 2015b; Darnley et al. 2014, 2015, 2016) with the Neil Gehrels Swift observatory was announced in ATel #11130. For additional follow-up coverage see ATels #11116, #11117, #11118, #11121, #11124, #11125, #11126, #11133, #11134, #11144, and #11149.

Here we report the end of the SSS phase around January 18. Following the last detection in a 6.2-ks Swift/XRT pointing on 2017-01-17.17 UT, with a count rate of (0.7±0.1) × 10-2 ct/s, no source was found in the subsequent 4.2-ks observation on 2017-01-18.24 UT (3σ upper limit of 0.3 × 10-2 ct/s). Consequently, we estimate an SSS turn-off time of less than 18 days after the likely eruption date on 2017-12-31.3 UT (see ATel #11149). This value is broadly consistent with the SSS turn-off observed for the eruptions in 2013 (day 19±1; Henze et al. 2014), 2014 (day 18.4±0.5; ATel #6604 and Henze et al. 2015a), and 2015 (day 18.6±0.7; ATel #8062 and Darnley et al. 2016); but is significantly longer than for the peculiar 2016 eruption (before day 16; ATel #9907 and Henze et al. 2018 submitted). All results are preliminary. A comprehensive multi-wavelength analysis is in preparation.

We wish to thank the Swift Team for the scheduling of the observations, in particular B. Cenko, the duty scientists, and the science planners.