Dead or alive? Long-term evolution of SN 2015bh (SNhunt275)

N. Elias-Rosa*, A. Pastorello, S. Benetti, E. Cappellaro, S. Taubenberger, G. Terreran, M. Fraser, P. J. Brown, L. Tartaglia, A. Morales-Garoffolo, J. Harmanen, N. D. Richardson, E. Artigau, L. Tomasella, R. Margutti, S. J. Smartt, M. Dennefeld, M. Turatto, G. C. Anupama, R. ArbourM. Berton, K. S. Bjorkman, T. Boles, F. Briganti, R. Chornock, F. Ciabattari, G. Cortini, A. Dimai, C. J. Gerhartz, K. Itagaki, R. Kotak, R. Mancini, F. Martinelli, D. Milisavljevic, K. Misra, P. Ochner, D. Patnaude, J. Polshaw, D. K. Sahu, S. Zaggia

*Corresponding author for this work

Research output: Contribution to journalArticle

27 Scopus citations

Abstract

Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of Mr ~ -13.4 mag, and was initially classified as an SN impostor. Here, we present the photometric and spectroscopic evolution of SN 2015bh from discovery to late phases (~1 yr after). In addition, we inspect archival images of the host galaxy up to ~21 yr before discovery, finding a burst ~1 yr before discovery, and further signatures of stellar instability until late 2014. Later on, the luminosity of the transient slowly increases, and a broad light-curve peak is reached after about three months. We propose that the transient discovered in early 2015 could be a core-collapse SN explosion. The pre-SN luminosity variability history, the long-lasting rise and faintness first light-curve peak suggests that the progenitor was a very massive, unstable and blue star, which exploded as a faint SN because of severe fallback of material. Later on, the object experiences a sudden brightening of 3 mag, which results from the interaction of the SN ejecta with circumstellar material formed through repeated past mass-loss events. Spectroscopic signatures of interaction are however visible at all epochs. A similar chain of events was previously proposed for the similar interacting SN 2009ip.

Original languageEnglish (US)
Pages (from-to)3894-3920
Number of pages27
JournalMonthly Notices of the Royal Astronomical Society
Volume463
Issue number4
DOIs
StatePublished - Dec 2016

Keywords

  • Galaxies: individual: NGC 2770
  • Stars: evolution
  • Supernovae: general
  • Supernovae: individual: SN 2009ip
  • Supernovae: individual: SN 2015bh

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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