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XMM-Newton X-ray detections of M31 novae in January 2016

ATel #8825; M. Henze (IEEC/CSIC), M. Sasaki (IAAT), F. Haberl (MPE), B. F. Williams (U. Washington), D. Hatzidimitriou (U. Athens / NOA), for a larger collaboration
on 16 Mar 2016; 12:42 UT
Credential Certification: Martin Henze (henze@ice.cat)

Subjects: X-ray, Nova, Transient

Referred to by ATel #: 8826, 8827

We report the X-ray detections of three novae in observations of the M31 northern disk by XMM-Newton in January 2016. In continuation of earlier observations described in ATels #8227 and #8228, a further two 100-ks observations were carried out on 2016-01-01 (ObsID 0763120401) and 2016-01-21 (ObsID 0763120201). The EPIC data were analysed using the standard reduction software. All count rates are given in the 0.2-4.5 keV band. The supersoft X-ray source (SSS) counterparts of two novae were already described in ATel #8228. The other nova was detected for the first time in X-rays. In follow-up ATels we will report on other new and recurrent X-ray transients detected in these observations.

Nova M31N 2006-08a, discovered on 2006-08-16.518 UT by K. Itagaki, was still faintly detected on Jan 21, 9.4 years (3445 d) after eruption. We estimated an EPIC count rate of (1.4±0.4) × 10-3 ct s-1 which is consistent with ATel #8228. All uncertainties are 1σ unless otherwise noted. A combined spectral analysis of all counts detected in 2015 and 2016 confirmed the SSS nature of the source and suggested the best-fit blackbody parameters kT = 45+15-10 eV and NH = (0.4±0.4) × 1021 cm-2. Based on the M31 nova population properties (Henze et al. 2014) the long SSS phase would suggest a blackbody temperature towards the lower end of the uncertainty range.

Nova M31N 2013-11d, which was discovered on 2013-11-25.3 UT (ATel #5605; see also ATel #5744), was still clearly detected on Jan 21, 2.2 years (788 d) after eruption. The EPIC count rate of (5.3±0.5) × 10-3 ct s-1 is consistent with the rates reported in ATel #8228. The X-ray spectrum of the nova appears to be unchanged. We estimated absorbed blackbody best-fit parameters of kT = 54+6-9 eV and NH = 1.6 +0.8-0.2 × 1021 cm-2, consistent with ATel #8228.

Nova M31N 2015-08c was discovered on 2015-08-27.07 UT (ATel #7963). It was spectroscopically classified as an Fe II nova with an H-alpha FWHM of 1560 km/s (ATel #8033). An X-ray counterpart was first detected on Jan 21, 0.4 years (148 d) after discovery, with an EPIC count rate of (4.2±0.4) × 10-3 ct s-1. The X-ray spectrum can be parametrised using an absorbed blackbody with best-fit values kT = 35±6 eV and NH = (0.4±0.4) × 1021 cm-2. The source is clearly an SSS. The correlations of Henze et al. 2014 suggest that the SSS phase will have a duration of several years.

The position of nova M31N 2012-06a, which was first detected in X-rays in 2014 (ATel #6564) and was still visible during our Jun 2015 observation (ATel #8228), was just outside the field of view of the recent observations.