Supernovae 2016bdu and 2005gl, and their link with SN 2009ip-like transients: another piece of the puzzle

Supernova (SN) 2016bdu is an unusual transient resembling SN 2009ip. SN\n2009ip-like events are characterized by a long-lasting phase of erratic\nvariability which ends with two luminous outbursts a few weeks apart. The\nsecond outburst is significantly more luminous (about 3 mag) than the first. In\nthe case of SN 2016bdu, the first outburst (Event A) reached an absolute\nmagnitude M(r) ~ -15.3 mag, while the second one (Event B) occurred over one\nmonth later and reached M(r) ~ -18 mag. By inspecting archival data, a faint\nsource at the position of SN 2016bdu is detectable several times in the past\nfew years. We interpret these detections as signatures of a phase of erratic\nvariability, similar to that experienced by SN 2009ip between 2008 and\nmid-2012, and resembling the currently observed variability of the luminous\nblue variable SN 2000ch in NGC 3432. Spectroscopic monitoring of SN 2016bdu\nduring the second peak initially shows features typical of a SN IIn. One month\nafter the Event B maximum, the spectra develop broad Balmer lines with P Cygni\nprofiles and broad metal features. At these late phases, the spectra resemble\nthose of a typical Type II SN. All members of this SN 2009ip-like group are\nremarkably similar to the Type IIn SN 2005gl. For this object, the claim of a\nterminal SN explosion is supported by the disappearance of the progenitor star.\nThe similarity with SN 2005gl suggests that all members of this family may\nfinally explode as genuine SNe, although the unequivocal detection of\nnucleosynthesised elements in their nebular spectra is still missing.\n