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

Elias-Rosa, N. ; Pastorello, A. ; Benetti, S. ; Cappellaro, E. ; Taubenberger, S. ; Terreran, G. ; Fraser, M. ; Brown, P. J. ; Tartaglia, L. ; Morales-Garoffolo, A. ; Harmanen, J. ; Richardson, N. D. ; Artigau, É. ; Tomasella, L. ; Margutti, R. ; Smartt, S. J. ; Dennefeld, M. ; Turatto, M. ; Anupama, G. C. ; Arbour, R. ; Berton, M. ; Bjorkman, K. S. ; Boles, T. ; Briganti, F. ; Chornock, R. ; Ciabattari, F. ; Cortini, G. ; Dimai, A. ; Gerhartz, C. J. ; Itagaki, K. ; Kotak, R. ; Mancini, R. ; Martinelli, F. ; Milisavljevic, D. ; Misra, K. ; Ochner, P. ; Patnaude, D. ; Polshaw, J. ; Sahu, D. K. ; Zaggia, S. (2016) Dead or alive? long-term evolution of SN 2015bh (SNhunt275) Monthly Notices of the Royal Astronomical Society, 463 (4). pp. 3894-3920. ISSN 0035-8711

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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 a 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.

Item Type:Article
Source:Copyright of this article belongs to Oxford University Press.
Keywords:Galaxies: Individual (NGC 2770); Stars: Evolution; Supernovae: General; Supernovae: Individual (SN 2015bh, SN 2009ip)
ID Code:100884
Deposited On:10 Dec 2016 12:03
Last Modified:10 Dec 2016 12:04

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