M31N 2008-12a - the remarkable recurrent nova in M31: Pan-chromatic observations of the 2015 eruption

• Published in: arXiv.org 2016-08
• Main Authors: Darnley, M J, Henze, M, Bode, M F, Hachisu, I, Hernanz, M, Hornoch, K, Hounsell, R, Kato, M, J -U Ness, Osborne, J P, Page, K L, V A R M Ribeiro, Rodriguez-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, Kucakova, 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, Z Xu
• Format: Article
• Language: English
• Subjects: Andromeda Galaxy; Collimation; Emission spectra; Galaxies; High temperature; Infrared photometry; Ionization; Near infrared radiation; Outflow; Photometry; Soft x rays; Spectrum analysis; White dwarf stars
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1607.08082

The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption ten times, including yearly eruptions from 2008-2014. With a measured recurrence period of \(P_\mathrm{rec}=351\pm13\) 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 2m (Hawaii) discovered the 2015 eruption, estimated to have commenced at Aug. \(28.28\pm0.12\) UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities \(\sim13000\) 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 super-soft 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 \(P_\mathrm{rec}=174\pm10\) d, and we expect the next eruption of M31N 2008-12a to occur around mid-Sep. 2016.