Radiation Mediated Shock and Planar Shock Breakout in the Presence of Atomic Transition Lines

Abstract

We numerically study fast Newtonian radiation mediated shocks (RMS - v/c~0.2) in two simplified problems in the context of supernova shock breakout; (1) An RMS traveling in a uniform medium, and (2) an RMS escaping a powerlaw density profile in planar geometry (\rho~x^n). Both problems were previously solved in the literature assuming a fully ionized plasma medium emitting Bremstrahllung. It was shown that at high shock velocities photons can deviate from local thermal equilibrium (LTE) and reach distributions peaked at many keV. In this study we incorporate, for the first time, opacity from bound species of heavy elements (solar-like composition) into these two problems, at times drastically augmenting the photon production due to bound-free and bound-bound radiative processes. We use a previously developed hydrodynamically coupled multi-group radiative diffusion code, including inelastic Compton scattering and frequency-dependent opacity from the publicly available TOPS table. Adding a more realistic opacity leads the radiation to maintain LTE at higher velocities in comparison to the fully ionized problem. In the planar SBO problem this opacity can reduce the emission temperature by half and even an order of magnitude. This result is important for the observation of supernova shock breakout emission. The SED of SN envelope breakout will very likely remain in LTE for explosions in red super giant stars without stellar wind (and part of blue super giant star explosions), making X-Ray observations less likely in these cases by orders of magnitude relative to previous predictions. We provide a semi-analytic description for the SED in the case where LTE is maintained. A correct shock-breakout calculation requires opacity tables that include bound yet highly ionized species, ruling out the use of certain line tables (such as the commonly used Kurucz table).