X-ray emission from radiative shocks in type II supernovae

Abstract

The X-ray emission from the circumstellar interaction in type II supernovae with a dense circumstellar medium is calculated. In type IIL and type IIn supernovae, mass loss rates are generally high enough for the region behind the reverse shock to be radiative, producing strong radiation, particularly in X-rays. We present a model for the emission from the cooling region in the case of a radiative reverse shock. Under the assumption of a stationary flow, a hydrodynamic model is combined with a time-dependent ionization balance and multilevel calculations. The applicability of the steady state approximation is discussed for various values of the ejecta density gradient and different sets of chemical composition. We show how the emerging spectrum strongly depends on the reverse shock velocity and the composition of the shocked gas. We discuss differences between a spectrum produced by this model and a single-temperature spectrum. Large differences are found especially for the line emission, which can seriously affect abundance estimates. We also illustrate the effects of absorption in the cool shocked ejecta. The applicability of our model to various types of supernovae is discussed.