094087

Late-time observations of type II supernovae (SNe II) are a window into theuncertain mass-loss history of their red supergiant (RSG) star progenitors aswell as a direct probe of the physics of shock interaction as SN ejecta collidewith distant circumstellar material (CSM). We propose target of opportunity(ToO) XMM observations of SNe II following UV/optical imaging through anapproved HST snapshot program. The novel combination of X-ray UV and opticalwavelengths will construct the first spectral energy distribution of its kindcapable of directly constraining the unknown thermalization efficiency ofradiation produced by the SN shock. These observations will also directlyconstrain the highly debated mass-loss histories of RSGs. [truncated! Please see actual data for full text]