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arXiv · 1401.2904

A remarkable recurrent nova in M31 - The X-ray observations

M. Henze·J. -U. Ness·M. J. Darnley·M. F. Bode·S. C. Williams·A. W. Shafter·M. Kato·I. Hachisu
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Abstract

Another outburst of the recurrent M31 nova M31N 2008-12a was announced in late November 2013. Optical data suggest an unprecedentedly short recurrence time of approximately one year. In this Letter we address the X-ray properties of M31N 2008-12a. We requested Swift monitoring observations shortly after the optical discovery. We estimated source count rates and extracted X-ray spectra from the resulting data. The corresponding ultraviolet (UV) data was also analysed. M31N 2008-12a was clearly detected as a bright supersoft X-ray source (SSS) only six days after the well-constrained optical discovery. It displayed a short SSS phase of two weeks duration and an exceptionally hot X-ray spectrum with an effective blackbody temperature of ~97 eV. During the SSS phase the X-ray light curve displayed significant variability that might have been accompanied by spectral variations. The very early X-ray variability was found to be anti-correlated with simultaneous variations in the UV flux. The X-ray properties of M31N 2008-12a coherently point towards a high-mass white dwarf in the nova system. This object might be a promising Type Ia supernova progenitor. We re-discovered additional X-ray detections of M31N 2008-12a that are consistent with our data and increase the number of known nova outbursts to seven. This nova is an exceptional object that merits further attention in the future.

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M. Henze, J. -U. Ness, M. J. Darnley, M. F. Bode, S. C. Williams, A. W. Shafter, M. Kato, I. Hachisu. 2014-01-13. A remarkable recurrent nova in M31 - The X-ray observations. https://doi.org/10.1051/0004-6361%2F201423410

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