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

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


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.


This is the final version of the article. It first appeared from Oxford University Press via


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

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Monthly Notices of the Royal Astronomical Society

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