The early UV/Optical emission from core-collapse supernovae

TL;DR

This paper presents a simplified model for the early UV/optical emission of core-collapse supernovae, linking observable features to progenitor properties and composition, and validates it with real supernova data.

Contribution

The authors develop a new approximate model for early supernova emission that accounts for opacity changes and spectral deviations, improving estimates of progenitor characteristics.

Findings

Early UV/optical emission constrains progenitor radius and composition.

Neglecting recombination can overestimate progenitor radius by over an order of magnitude.

Model predictions are consistent with observations of SN2008D and SNLS-04D2dc.

Abstract

We derive a simple approximate model describing the early, hours to days, UV/optical supernova emission, which is produced by the expansion of the outer <~0.01 solar mass part of the shock-heated envelope, and precedes the optical emission driven by radioactive decay. Our model includes an approximate description of the time dependence of the opacity (due mainly to recombination), and of the deviation of the emitted spectrum from a black body spectrum. We show that the characteristics of the early UV/O emission constrain the radius of the progenitor star, its envelope composition, and the ratio of the ejecta energy to its mass, E/M. For He envelopes, neglecting the effect of recombination may lead to an over estimate of progenitor radius by more than an order of magnitude. We also show that the relative extinction at different wavelengths may be inferred from the light-curves at these wave-lengths, removing the uncertainty in the estimate of progenitor radius due to reddening (but not the uncertainty in E/M due to uncertainty in absolute extinction). The early UV/O observations of the type Ib SN2008D and of the type IIp SNLS-04D2dc are consistent with our model predictions. For SN2008D we find progenitor radius to be approx. 10^11 cm, and an indication that the He envelope contains a significant C/O fraction.