CALTECH CORE-COLLAPSE PROJECT (CCCP) OBSERVATIONS OF TYPE IIn SUPERNOVAE: TYPICAL PROPERTIES AND IMPLICATIONS FOR THEIR PROGENITOR STARS

Abstract

Type IIn Supernovae (SNe IIn) are rare events, constituting only a few\npercent of all core-collapse SNe, and the current sample of well observed SNe\nIIn is small. Here, we study the four SNe IIn observed by the Caltech\nCore-Collapse Project (CCCP). The CCCP SN sample is unbiased to the extent that\nobject selection was not influenced by target SN properties. Therefore, these\nevents are representative of the observed population of SNe IIn. We find that a\nnarrow P-Cygni profile in the hydrogen Balmer lines appears to be a ubiquitous\nfeature of SNe IIn. Our light curves show a relatively long rise time (>20\ndays) followed by a slow decline stage (0.01 to 0.15 mag/day), and a typical\nV-band peak magnitude of M_V=-18.4 +/- 1.0 mag. We measure the progenitor star\nwind velocities (600 - 1400 km/s) for the SNe in our sample and derive\npre-explosion mass loss rates (0.026 - 0.12 solar masses per year). We compile\nsimilar data for SNe IIn from the literature, and discuss our results in the\ncontext of this larger sample. Our results indicate that typical SNe IIn arise\nfrom progenitor stars that undergo LBV-like mass-loss shortly before they\nexplode.\n