Padova-Asiago Supernova Group

Dead or Alive? Long-time evolution of SN 2015bh (SNhunt275)
Elias-Rosa, N., et al. 2016 MNRAS submitted (arXiv:1606.09024
  (link to pdf)

Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of Mr ~ -13 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 ~ 16 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.

sn galaxy RA DEC discoverer type redshift ref class fits
SDSS J234711.91+1004 23:47:11.64 +10:04:59.56 ASASSN Ia 0.034 ATEL
  02:49:42.76 +46:34:36.6 PSST SN Ia 0.028 ATEL
2MASX J23203937+4823 23:20:38.50 +48:23:29.59 PSST II 0.044 ATEL
NPM1G +62.0196 16:26:29.21 +62:05:32.05 PSST Ia 0.052 ATEL
UGC 482 00:46:29.27 +08:25:58.85 PSST Ia 0.040 ATEL