Recurrent nova M31N 2008-12a: Swift XRT spectrum confirms supersoft X-ray emission
ATel #6565; 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 10 Oct 2014; 16:46 UT
Credential Certification: Martin Henze (martin.henze@sciops.esa.int)
Subjects: X-ray, Nova, Transient
Referred to by ATel #: 6604
In ATel #6558 we reported the first detection of supersoft X-ray source (SSS) emission following the most recent outburst of the remarkable recurrent nova M31N 2008-12a (see ATel #6527). This detection was made on 2014-10-08.29 UT, about six days after outburst. During the following Swift XRT monitoring observation on 2014-10-09.02 UT the source continued to brighten and about 70 counts were collected in 4.4 ks. Here we report on the spectral analysis of the extracted source counts from both observations.
The X-ray spectrum of the source can be described using a blackbody model with best-fit temperature of (54+10-9) eV and NH = (1.6+1.0-0.7) × 1021 cm-2 (1σ confidence ranges for the statistical uncertainty). All of the approximately 100 source counts (from both observations combined) have energies below 1 keV. The spectrum clearly confirms the SSS nature of the source. The estimated effective temperature is consistent with the early X-ray spectrum of M31N 2008-12a during the 2013 outburst (ATel #5627, Henze et al. 2014). The X-ray light curve shows irregular short-term variability similar to the 2013 outburst (ATel #5633).
Erratum: In ATel #6558 we claimed wrongly that M31N 2008-12a is the nova with the fastest SSS turn on in any galaxy. This record in fact belongs to the Galactic recurrent nova V745 Sco (SSS turn on 3-4 d, see ATel #5870). We wish to thank F. Walter for pointing this out to us.
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.
