The Optical to X-ray Luminosity and Spectra of Supernova Wind Breakouts

I will discuss our recent work on the breakout of SN shock waves through extended dense circumstellar medium (CSM), which observations indicate is common at radii of 10¹⁴ – 10¹⁵ cm around core-collapse SN progenitors. The breakout of the radiation-mediated shock (RMS) through such CSM leads to the formation of a collisionless shock (CLS). We analyzed the evolution of the shock structure and associated radiation field during and after the RMS-CLS transition for non-relativistic breakouts, providing an analytic description of the key properties of the emitted optical to X-ray radiation, supported by numeric radiation-hydrodynamics calculations. I will show that the characteristic photon energy shifts from the UV to X-rays as the shock moves to a few breakout radii on a few breakout timescales (days), and that the X-ray signal is not suppressed by propagation through the upstream wind. Upcoming surveys that will systematically detect large numbers of young SNe will enable the use of these results to infer the pre-explosion mass loss history of the SN progenitor population.