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, 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. Arbour, M. BertonK. 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

26 Citations (Scopus)

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
Pages (from-to)3894-3920
JournalMonthly Notices of the Royal Astronomical Society
Volume463
Issue number4
Early online date07 Sep 2016
DOIs
Publication statusPublished - 01 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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    Elias-Rosa, N., Pastorello, A., Benetti, S., Cappellaro, E., Taubenberger, S., Terreran, G., Fraser, M., Tartaglia, L., Morales-Garoffolo, A., Harmanen, J., Richardson, N. D., Artigau, E., Tomasella, L., Margutti, R., Smartt, S. J., Dennefeld, M., Turatto, M., Anupama, G. C., Arbour, R., ... Zaggia, S. (2016). Dead or alive? Long-term evolution of SN 2015bh (SNhunt275). Monthly Notices of the Royal Astronomical Society, 463(4), 3894-3920. https://doi.org/10.1093/mnras/stw2253