Outbursts from evolved massive stars: SN 2015bh and its relatives

摘要

In their final stages, massive stars can show large eruptions which can resemble core-collapse Iln SNe. Here we present SN 2015bh in NGC 2770, a IIn/impostor, where archival data show variabilities for at least 21 years before the main event in 2015. Serendipitous spectra during an outburst are the only SN progenitor spectra available since SN 1987A and show an LBV with a fast, dense outflow. Analogues to SN 2015bh are SN 2009ip and SNhunt 248 while the SN 2000ch impostor could be equivalent to the outburst phase of SN 2015bh. It is currently unclear whether SN 2015bh (and SN 2009ip) were final core-collapse events. Alternatively, they might be large outbursts shedding the outer envelope and creating a Wolf-Rayet star in only a matter of decades. Future large-scale high-cadence surveys such as LSST will detect many more of these events and allow us a unique insight into the largely unknown late stages of massive stellar evolution.