Double-peaked Supernovae and the Signature of Progenitors with Low-mass Extended Envelopes

Early observations of supernova light curves are powerful tools for shedding light on the pre-explosion structures of their progenitors and their mass-loss histories just prior to explosion. Some core-collapse supernovae that are detected during the first days after the explosion prominently show two peaks in the optical bands, where the first is presumably powered by the cooling of shocked surface material and the second peak is clearly powered by radioactive decay. Here we explore, first, whether this type of light curve can be generated by a progenitor with a “standard” density profile, such as a red supergiant or a Wolf-Rayet star. We find that such a progenitor: (i) cannot produce a double-peaked light curve in the R and I bands, and (ii) cannot exhibit a fast drop in the bolometric luminosity as is seen after the first peak. We then explore the signature of a progenitor with a massive, compact core surrounded by extended, low-mass material. This may be a hydrostatic low-mass envelope or material ejected just prior to the explosion. We show that it naturally produce both of these features. We use this result to provide simple formulae to estimate: (i) the mass of the extended material from the time of the first peak, (ii) the extended material radius from the luminosity of the first peak, and (iii) an upper limit on the core radius from the luminosity minimum between the two peaks. Subject headings: hydrodynamics — shock waves — supernovae: general