Deep Late-Time Observations of the Supernova Impostors SN 1954J and SN 1961V

Abstract

SN 1954J in NGC 2403 and SN 1961V in NGC 1058 were two luminous transients whose definitive classification as either non-terminal eruptions or supernovae remains elusive. A critical question is whether a surviving star can be significantly obscured by dust formed from material ejected during the transient. We use three lines of argument to show that the candidate surviving stars are not significantly optically extincted ($τ\lesssim 1$) by dust formed in the transients. First, we use SED fits to new HST optical and near-IR photometry. Second, neither source is becoming brighter as required by absorption from an expanding shell of ejected material. Third, the ejecta masses implied by the H$α$ luminosities are too low to produce significant dust absorption. The latter two arguments hold independent of the dust properties. The H$α$ fluxes should also be declining with time as $t^{-3}$, and this seems not to be observed. As a result, it seems unlikely that recently formed dust can be responsible for the present faintness of the sources compared to their progenitors, although this can be verified with \textit{JWST}. This leaves three possibilities: 1) the survivors were misidentified; 2) they are intrinsically less luminous; 3) SN 1954J and SN 1961V were true supernovae.