The Supernova Impostors

Abstract

The ''supernova impostors'' in nearby galaxies mimic the appearance of atrue supernova, but rather than a terminal explosion, the impostorsappear to be massive stars that have undergone a powerful eruption.Several of these have energetics comparable to true supernovae, and may,in fact, be analogous to the Great Eruption of {η} Carinae in the1800s. We distinguish the observed characteristics of impostors fromtrue supernovae. We discuss in detail the prototypical impostor, SN1961V. We also discuss other known examples where available data implythat these are also impostors. Finally, we connect the impostors to truesupernova events{\mdash}in other words, several recent supernovae appearto have progenitors which experienced high mass-loss events immediatelyprior to explosion, with one case clearly having an impostor-likeeruption only 2 years before discovery as a supernova. The supernovaimpostors represent rare instances of analogs to {η} Car and otherknown luminous blue variables from which we can acquire importantinsight into the final stages in the evolution of very massive stars.