Very massive stars in the final phases of their lives often show unpredictable outbursts that can mimic supernovae , so-called , ‘ ‘ SN impostors ’ ’ , but the distinction is not always straigthforward .
Here we present observations of a luminous blue variable ( LBV ) in NGC 2770 in outburst over more than 20 years that experienced a possible terminal explosion as type IIn SN in 2015 , named SN 2015bh .
This possible SN or ‘ ‘ main event ’ ’ was preceded by a precursor peaking \sim 40 days before maximum .
The total energy release of the main event is \sim 1.8 \times 10 ^ { 49 } erg , which can be modeled by a < 0.5 M _ { \odot } shell plunging into a dense CSM .
All emission lines show a single narrow P-Cygni profile during the LBV phase and a double P-Cygni profile post maximum suggesting an association of this second component with the possible SN .
Since 1994 the star has been redder than during a typical S-Dor like outburst .
SN 2015bh lies within a spiral arm of NGC 2770 next to a number of small star-forming regions with a metallicity of \sim 0.5 solar and a stellar population age of 7–10 Myr .
SN 2015bh shares many similarities with SN 2009ip , which , together with other examples may form a new class of objects that exhibit outbursts a few decades prior to ‘ ‘ hyper-eruption '' or final core-collapse .
If the star survives this event it is undoubtedly altered , and we suggest that these ‘ ‘ zombie stars '' may evolve from an LBV to a Wolf Rayet star over a very short timescale of only a few years .
The final fate of these types of massive stars can only be determined with observations years after the possible SN .