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X-ray emission of nova M31N 2014-02a detected with Swift

ATel #6374; R. Sturm (MPE), M. Henze (ESAC/ESA), J. Greiner (MPE), W. Pietsch (MPE), F. Haberl (MPE)
on 7 Aug 2014; 11:51 UT
Credential Certification: Richard Sturm (rsturm@mpe.mpg.de)

Subjects: X-ray, Nova, Transient

Referred to by ATel #: 6564

We report the discovery of an X-ray transient in monitoring observations of the central region of the Andromeda Galaxy (M 31) with the X-ray telescope on board the Swift satellite. The source is located at RA = 00:43:26.66 Dec = +41:23:30.8 (J2000, total coordinate uncertainty 4.2", 90% confidence level). The energy of the bulk of the detected photons is below 1 keV, pointing to a super-soft X-ray spectrum. Light-curve information is given in the table below, including 3σ upper limits.

ObsID        Exp   Date            Rate   
             [ks]  (UT)            [10-3 ct s-1]  
00032702058  3.6   2014-06-11.82   <6.3       
00032702059  3.3   2014-06-19.01   <6.1       
00032702060  3.6   2014-06-27.00   <3.5       
00032702061  3.9   2014-07-05.67   5.1±1.5  
00032702062  4.2   2014-07-13.74   2.1±1.0  
00032702063  4.0   2014-07-21.00   <6.8       
00032702066  3.4   2014-08-01.19   5.4±1.7  

The position of the X-ray source is in agreement with the M 31 nova 2014-02a (ATel #5844) having an angular separation of 2.7". It was classified as a He/N nova with a high expansion velocity (ATel #5852). These novae tend to have short X-ray turn on times and harder X-ray spectra compared to FeII novae (Henze et al. 2014, A&A, 563A, 2), which is consistent with the X-ray emission reported here. We first detected the nova in X-rays about 150 days after the optical discovery. This is a relatively short turn-on time of the supersoft X-ray emission (cf. Henze et al. 2014). The X-ray light curve might suggest variability. A variable flux during the early stages of the supersoft X-ray phase has been observed for several M 31 and Galactic novae (e.g. ATels #4727, #5633).

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