Shell-shocked Diffusion Model for the Light Curve of SN 2006gy

Abstract

We explore a simple model for the high luminosity of SN 2006gy involving photon diffusion of shock-deposited thermal energy. The distinguishing property of the model is that the large “stellar” radius of ∼160 AU required to prevent adiabatic losses is not the true stellar radius, but rather, it is the radius of an opaque, unbound circumstellar envelope, created when ∼10 M, was ejected in the decade before the supernova in an eruption analogous to that of h Carinae. The supernova light is produced primarily by diffusion of thermal energy following the passage of the blast wave through this shell. This model differs from traditional models of supernova debris interacting with an external circumstellar medium (CSM) in that here the shell is optically thick and the escape of radiation is delayed. We show that any model attempting to account for SN 2006gy’s huge luminosity with radiation emitted by ongoing CSM interaction fails for the following basic reason: the CSM density required to achieve the observed luminosity makes the same circumstellar envelope opaque ( ), forcing a thermal t 300 diffusion solution. In our model, the weaker CSM interaction giving rise to SN 2006gy’s characteristic Type IIn spectrum and soft X-rays is not linked to the power source of the visual continuum; instead, it arises after the blast wave breaks free from the opaque shell into the surrounding wind. While a simple diffusion model can explain the gross properties of the early light curve of SN 2006gy, it predicts that the light curve must plummet rapidly at late times, unless an additional power source is present. Subject headings: circumstellar matter — stars: evolution — supernovae: individual (SN 2006gy)