Breaking the habit - the peculiar 2016 eruption of the unique recurrent nova M31N 2008-12a

Henze, M. and Darnley, M. J. and Williams, S. C. and Kato, M. and Hachisu, I. and Anupama, G. C. and Arai, A. and Boyd, D. and Burke, D. and Chinetti, K. and Ciardullo, R. and Cook, L. M. and Cook, M. J. and Erdman, P. and Gao, X. and Harris, B. and Hartmann, D. H. and Hornoch, K. and Horst, J. Chuck and Hounsell, R. and Husar, D. and Itagaki, K. and Kabashima, F. and Kafka, S. and Kaur, A. and Kiyota, S. and Kojiguchi, N. and Kucakova, H. and Kuramoto, K. and Maehara, H. and Mantero, A. and Masci, F. J. and Matsumoto, K. and Naito, H. and Ness, J. -U. and Nishiyama, K. and Oksanen, A. and Osborne, J. P. and Page, K. L. and Paunzen, E. and Pavana, M. and Pickard, R. and Prieto-Arranz, J. and Rodriguez-Gil, P. and Sala, G. and Sano, Y. and Shafter, A. W. and Sugiura, Y. and Tan, H. and Tordai, T. and Vratil, J. and Wagner, R. M. and Watanabe, F. and Williams, B. F. and Bode, M. F. and Bruno, A. and Buchheim, B. and Crawford, T. and Goff, B. and Hernanz, M. and Igarashi, A. S. and Jose, J. and Motta, M. and O'Brien, T. J. and Oswalt, T. and Poyner, G. and Ribeiro, V. A. R. M. and Sabo, R. and Shara, M. M. and Shears, J. and Starkey, D. and Starrfield, S. and Woodward, C. E. (2018) Breaking the habit - the peculiar 2016 eruption of the unique recurrent nova M31N 2008-12a. The Astrophysical Journal. ISSN 0004-637X

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Abstract

Since its discovery in 2008, the Andromeda galaxy nova M31N 2008-12a has been observed in eruption every single year. This unprecedented frequency indicates an extreme object, with a massive white dwarf and a high accretion rate, which is the most promising candidate for the single-degenerate progenitor of a type-Ia supernova known to date. The previous three eruptions of M31N 2008-12a have displayed remarkably homogeneous multi-wavelength properties: (i) From a faint peak, the optical light curve declined rapidly by two magnitudes in less than two days; (ii) Early spectra showed initial high velocities that slowed down significantly within days and displayed clear He/N lines throughout; (iii) The supersoft X-ray source (SSS) phase of the nova began extremely early, six days after eruption, and only lasted for about two weeks. In contrast, the peculiar 2016 eruption was clearly different. Here we report (i) the considerable delay in the 2016 eruption date, (ii) the significantly shorter SSS phase, and (iii) the brighter optical peak magnitude (with a hitherto unobserved cusp shape). Early theoretical models suggest that these three different effects can be consistently understood as caused by a lower quiescence mass-accretion rate. The corresponding higher ignition mass caused a brighter peak in the free-free emission model. The less-massive accretion disk experienced greater disruption, consequently delaying re-establishment of effective accretion. Without the early refueling, the SSS phase was shortened. Observing the next few eruptions will determine whether the properties of the 2016 outburst make it a genuine outlier in the evolution of M31N 2008-12a.

Item Type:
Journal Article
Journal or Publication Title:
The Astrophysical Journal
Additional Information:
This is an author-created, un-copyedited version of an article accepted for publication/published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi:10.3847/1538-4357/aab6a6
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/1900/1912
Subjects:
ID Code:
125367
Deposited By:
Deposited On:
22 May 2018 09:28
Refereed?:
Yes
Published?:
Published
Last Modified:
18 Sep 2020 04:14