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

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11 Citations (Scopus)


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 Mo 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.

Original languageEnglish
Article number40
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2016 Oct 10


  • X-rays: binaries
  • cataclysmic variables
  • novae
  • stars: individual (M31N 2008-12a)
  • white dwarfs

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Kato, M., Saio, H., Henze, M., Ness, J. U., Osborne, J. P., Page, K. L., Darnley, M. J., Bode, M. F., Shafter, A. W., Hernanz, M., Gehrels, N., Kennea, J., & Hachisu, I. (2016). X-RAY FLASHES in RECURRENT NOVAE: M31N 2008-12a and the IMPLICATIONS of the SWIFT NONDETECTION. Astrophysical Journal, 830(1), [40]. https://doi.org/10.3847/0004-637X/830/1/40