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

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.; José, 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.
Bibliographical reference

The Astrophysical Journal, Volume 833, Issue 2, article id. 149, 38 pp. (2016).

Advertised on:
12
2016
Number of authors
55
IAC number of authors
1
Citations
102
Refereed citations
50
Description
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 {P}{rec}=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 ˜13,000 km s-1, 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 {P}{rec}=174+/- 10 days, and we expect the next eruption of M31N 2008-12a to occur around 2016 mid-September.