M31N 2008-12a - the remarkable recurrent nova in M31: Pan-chromatic observations of the 2015 eruption
Creators: name: Darnley, M. J.
name: Henze, M.
name: Bode, M. F.
name: Hachisu, I.
name: Hernanz, M.
name: Hornoch, K.
name: Hounsell, R.
name: Kato, M.
name: Ness, J. -U.
name: Osborne, J. P.
name: Page, K. L.
name: Ribeiro, V. A. R. M.
name: Rodriguez-Gil, P.
name: Shafter, A. W.
name: Shara, M. M.
name: Steele, I. A.
name: Williams, S. C.
name: Arai, A.
name: Arcavi, I.
name: Barsukova, E. A.
name: Boumis, P.
name: Chen, T.
name: Fabrika, S.
name: Figueira, J.
name: Gao, X.
name: Gehrels, N.
name: Godon, P.
name: Goranskij, V. P.
name: Harman, D. J.
name: Hartmann, D. H.
name: Hosseinzadeh, G.
name: Horst, J. Chuck
name: Itagaki, K.
name: Jose, J.
name: Kabashima, F.
name: Kaur, A.
name: Kawai, N.
name: Kennea, J. A.
name: Kiyota, S.
name: Kucakova, H.
name: Lau, K. M.
name: Maehara, H.
name: Naito, H.
name: Nakajima, K.
name: Nishiyama, K.
name: O'Brien, T. J.
name: Quimby, R.
name: Sala, G.
name: Sano, Y.
name: Sion, E. M.
name: Valeev, A. F.
name: Watanabe, F.
name: Watanabe, M.
name: Williams, B. F.
name: Xu, Z.
Publisher: name: arXiv
Year: 2016
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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.
description: 46 pages, 19 figures, 14 tables, accepted for publication in ApJ (accepted version, minor changes made during the refereeing process)