M 31 novae M31N 2012-06a and M31N 2014-02a detected in X-rays with XMM-Newton

ATel #6564; M. Henze (ESAC/ESA), R. Sturm (MPE), J.-U. Ness (ESAC/ESA), J. Greiner (MPE), M. Della Valle (INAF-Napoli), G. Sala (UPC-IEEC), M. Hernanz (CSIC-IEEC), A. W. Shafter (SDSU), K. Hornoch (Ondrejov), M. Orio (INAF-Padova), D. H. Hartmann (Clemson), A. Kaur (Clemson), D. Hatzidimitriou (Athens), M. Middleton (Cambridge)
on 10 Oct 2014; 09:31 UT
Credential Certification: Martin Henze (martin.henze@sciops.esa.int)

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We report the detection of two M 31 novae as supersoft X-ray sources (SSS) in a recent XMM-Newton target of opportunity (ToO) observation. The 24 ks observation was obtained on 2014-08-09.89 UT to study the SSS emission of nova M31N 2014-02a, previously detected by Swift (ATel #6374). The second SSS, the counterpart of nova M31N 2012-06a, was serendipitously discovered in the field of view.

M31N 2014-02a was discovered in the optical by the intermediate Palomar Transient Factory on 2014-02-02.1 UT (ATel #5844) and first seen in X-rays 155 days later on 2014-07-05.67 UT (ATel #6374). The XMM-Newton EPIC pn and MOS spectra taken on day 190 after outburst showed the object to be a SSS with an effective (blackbody) best-fit temperature of (64±6) eV and absorption of N_H = (4.4±1.0) × 10²¹ cm^-2 (1σ confidence ranges). The high absorption in this model (Galactic foreground at N_H ~ 0.7 × 10²¹ cm^-2) might point towards intrinsic absorption and/or inadequacies of the blackbody parametrisation. Note, that the projected position of the nova is located on a dust lane in the NIR study of Montalto et al. (2009). The observed count rate was (1.9±0.1) × 10^-2 ct s^-1.

M31N 2012-06a was discovered in the optical by K. Hornoch and P. Kusnirak on 2012-06-18.052 UT (ATel #4186). It was spectroscopically classified as a FeII nova (ATel #4216) and observed as a UV source with Swift (ATels #4281,#4757). Within the XMM-Newton ToO observation, we detected an X-ray counterpart serendipitously with (9.6±0.7) × 10^-3 ct s^-1 on day 782 after the optical discovery. The EPIC pn and MOS spectra can be described using an absorbed blackbody model with best-fit kT = (41±5) eV and N_H = (0.7±0.3) × 10²¹ cm^-2 (1σ confidence ranges). The N_H is consistent with the Galactic foreground. This source is clearly a SSS with a relatively low temperature and relatively long SSS phase, in agreement with the M 31 nova population properties (Henze et al. 2014).

We would like to thank the XMM-Newton team for the rapid and efficient scheduling of the ToO observations.