Padova-Asiago Supernova Group

Interacting supernovae and supernova impostors. LSQ13zm: an outburst heralds the death of a massive star
Tartaglia et al. 2016 MNRAS 459, 1039
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We report photometric and spectroscopic observations of the optical transient LSQ13zm. Historical data reveal the presence of an eruptive episode (that we label as 2013a) followed by a much brighter outburst (2013b) three weeks later, that we argue to be the genuine supernova explosion. This sequence of events closely resem- ble those observed for SN 2010mc and (in 2012) SN 2009ip. The absolute magnitude reached by LSQ13zm during 2013a (MR = 14.87+/-0.25 mag) is comparable with those of supernova impostors, while that of the 2013b event (MR = 18.46 +/- 0.21 mag) is consistent with those of interacting supernovae. Our spectra reveal the presence of a dense and structured circumstellar medium, probably produced through numerous pre-supernova mass-loss events. In addition, we find evidence for high-velocity ejecta, with a fraction of gas expelled at more than 20000km s1. The spectra of LSQ13zm show remarkable similarity with those of well-studied core-collapse supernovae. From the analysis of the available photometric and spectroscopic data, we conclude that we first observed the last event of an eruptive sequence from a massive star, likely a Lu- minous Blue Variable, which a short time later exploded as a core-collapse supernova. The detailed analysis of archival images suggest that the host galaxy is a star-forming Blue Dwarf Compact Galaxy. 76