X-ray Flashes in Recurrent Novae: M31N 2008-12a and the Implications of the Swift Nondetection
Abstract
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}⊙ and for two recurrence periods of 0.5 and 1 yr. 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 hr (0.6 days) among the four cases is obtained for the 1.385 {M}⊙ WD with a 1 yr 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 yr recurrence period), which resulted in the nondetection 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 essential for understanding the pre-optical-maximum phase. We encourage further observations.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2016
- DOI:
- 10.3847/0004-637X/830/1/40
- arXiv:
- arXiv:1607.07985
- Bibcode:
- 2016ApJ...830...40K
- Keywords:
-
- novae;
- cataclysmic variables;
- stars: individual: M31N 2008-12a;
- white dwarfs;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 12 pages, including 9 figures and 3 tables. To appear in the Astrophysical Journal