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

Journal
Date Issued
2016
Author(s)
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Taubenberger, S.
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Terreran, G.
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Fraser, M.
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Brown, P. J.
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Morales-Garoffolo, A.
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Harmanen, J.
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Richardson, N. D.
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Artigau, É.
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Margutti, R.
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Smartt, S. J.
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Dennefeld, M.
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Anupama, G. C.
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Arbour, R.
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Berton, M.
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Bjorkman, K. S.
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Boles, T.
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Briganti, F.
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Chornock, R.
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Ciabattari, F.
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Cortini, G.
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Dimai, A.
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Gerhartz, C. J.
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Itagaki, K.
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Kotak, R.
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Mancini, R.
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Martinelli, F.
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Milisavljevic, D.
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Misra, K.
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Ochner, P.
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Patnaude, D.
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Polshaw, J.
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Sahu, D. K.
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DOI
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.
Volume
463
Issue
4
Start page
3894
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2016MNRAS.463.3894E
Rights
open.access
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