Recurrent nova M31N 2008-12a: The 2018 X-ray turn-off seen by Swift/XRT
ATel #12241; 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 26 Nov 2018; 11:56 UT
Credential Certification: Martin Henze (henze@ice.cat)
Subjects: X-ray, Nova, Transient
Previously, we announced the detection (ATel #12207) of supersoft X-ray source (SSS) emission from the 2018 eruption (ATel #12177) of the rapidly recurring nova M31N 2008-12a (Darnley et al. 2014, 2015, 2016) and Henze et al. (2014, 2015a, 2015b, 2018). Additional optical/UV photometry and optical spectroscopy of the 2018 eruption was published in ATels #12179, #12181, #12182, #12189, #12190, #12195, #12200, #12203, #12204, #12205.
Here we report the disappearance of the SSS emission back towards quiescence on November 25th. The entire 2018 eruption was monitored by the Neil Gehrels Swift observatory and a comprehensive multi-wavelength analysis is in preparation following these preliminary findings: After the last detection in a 6.1-ks Swift/XRT pointing on 2018-11-24.45 UT, with a faint count rate of (0.3±0.1) × 10-2 ct/s, no source was found in the subsequent 4.7-ks observation on 2018-11-25.12 UT (3σ upper limit of 0.3 × 10-2 ct/s). Consequently, we estimate an SSS turn-off time of around 18 days after the discovery date on 2018-11-06.80 UT (ATel #12177).
This SSS turn-off time is overall consistent with the equivalent time scales 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), 2015 (day 18.6±0.7; ATel #8062 and Darnley et al. 2016), and 2017 (prior to day 18; ATel #11214 and Henze et al. in preparation). We note that all these time scales are significantly longer than for the peculiar 2016 eruption where the SSS phase had ended before day 16 (ATel #9907 and Henze et al. 2018).
We wish to thank the Swift Team for the scheduling of the observations and for the successful 2018 monitoring campaign, in particular B. Cenko, the duty scientists, and the science planners.
