M31N 2008-12a-The Remarkable Recurrent Nova in M31-Panchromatic Observations of the 2015 Eruption

• Published in: Astrophysical journal. Letters Vol. 833; no. 2
• Main Authors: Darnley, M. J., Henze, M., Bode, M. F., Hachisu, I., Hernanz, M., Hornoch, K., Hounsell, R., Kato, M., Ness, J.- U., Osborne, J. P., Page, K. L., Ribeiro, V. A. R. M., Rodríguez-Gil, P., Shafter, A. W., Shara, M. M., Steele, I. A., Williams, S. C., Arai, A., Arcavi, I., Barsukova, E. A., Boumis, P., Chen, T., Fabrika, S., Figueira, J., Gao, X., Gehrels, N., Godon, P., Goranskij, V. P., Harman, D. J., Hartmann, D. H., Hosseinzadeh, G., Horst, J. Chuck, Itagaki, K., Jose, J., Kabashima, F., Kaur, A., Kawai, N., Kennea, J. A., Kiyota, S., KuČáková, H., Lau, K. M., Maehara, H., Naito, H., Nakajima, K., Nishiyama, K., O’Brien, T. J., Quimby, R., Sala, G., Sano, Y., Sion, E. M., Valeev, A. F., Watanabe, F., Watanabe, M., Williams, B. F., Xu, Z.
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center The American Astronomical Society 13.12.2016
• Subjects: Astrophysics; Galaxies: Individual (m31) €“ Novae; Cataclysmic Variables €“ Stars: Individual (m31n 2008-12a) Â
• ISSN: 2041-8205; 2041-8213

The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption 10 times, including yearly eruptions from 2008 to 2014. With a measured recurrence period of Prec = 351+/-13 days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground- and space-based follow-up programs. In this paper we present the 2015 detection, visible to near-infrared photometry and visible spectroscopy, and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2 m (Hawaii) discovered the 2015 eruption, estimated to have commenced at August 28.28 +/- 0.12 UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities approx. 13,000 km/s, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early supersoft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze et al. (2015a), the updated recurrence period based on all known eruptions is Prec 174 +/- 10 days, and we expect the next eruption of M31N 2008-12a to occur around 2016 mid-September.