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

Published version
Peer-reviewed

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Authors

Elias-Rosa, N 
Pastorello, A 
Benetti, S 
Cappellaro, E 
Taubenberger, S 

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.

Description

This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw2253

Keywords

stars: evolution, supernovae: general, supernovae: individual: SN 2015bh, supernovae: individual: SN 2009ip, galaxies: individual: NGC 2770

Journal Title

Monthly Notices of the Royal Astronomical Society

Conference Name

Journal ISSN

0035-8711
1365-2966

Volume Title

463

Publisher

Oxford University Press (OUP)
Sponsorship
European Research Council under the European Union's Seventh Framework Programme, Science and Technology Facilities Council