X-Ray Flashes in Recurrent Novae: M31N 2008-12a and the Implications of the Swift Non-detection

27 Jul 2016  ·  Kato Mariko, Saio Hideyuki, Henze Martin, Ness Jan-Uwe, Osborne Julian P., Page Kim L., Darnley Matthew J., Bode Michael F., Shafter Allen W., Hernanz Margarita, Gehrels Neil, Kennea Jamie, Hachisu Izumi ·

Models of nova outbursts suggest that an X-ray flash should occur just after hydrogen ignition. However, this X-ray flash has never been observationally confirmed... We present four theoretical light curves of the X-ray flash for two very massive white dwarfs (WDs) of 1.380 and 1.385 M_sun and for two recurrence periods of 0.5 and 1 years. The duration of the X-ray flash is shorter for a more massive WD and for a longer recurrence period. The shortest duration of 14 hours (0.6 days) among the four cases is obtained for the 1.385 M_sun WD with one year recurrence period. In general, a nova explosion is relatively weak for a very short recurrence period, which results in a rather slow evolution toward the optical peak. This slow timescale and the predictability of very short recurrence period novae give us a chance to observe X-ray flashes of recurrent novae. In this context, we report the first attempt, using the Swift observatory, to detect an X-ray flash of the recurrent nova M31N 2008-12a (0.5 or 1 year recurrence period), which resulted in the non-detection of X-ray emission during the period of 8 days before the optical detection. We discuss the impact of these observations on nova outburst theory. The X-ray flash is one of the last frontiers of nova studies and its detection is essentially important to understand the pre-optical-maximum phase. We encourage further observations. read more

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High Energy Astrophysical Phenomena Solar and Stellar Astrophysics