Thermal X-ray Emission and Cosmic Ray Production in Young Supernova Remnants

We have developed a simple model to investigate the modifications of the hydrodynamics and non-equilibrium ionization X-ray emission in young supernova remnants due to nonlinear particle acceleration. In nonlinear, diffusive shock acceleration, the heating of the gas to X-ray emitting temperatures is strongly coupled to the acceleration of cosmic ray ions. If the acceleration is efficient and a significant fraction of the shock ram energy ends up in cosmic rays, compression ratios will be higher and the shocked temperature lower than test-particle, Rankine-Hugoniot relations predict. In this Letter, we show that typical parameters of young supernova remnants should result in significant nonlinear acceleration, which strongly modifies the hydrodynamics and consequently the thermal X-ray emission. We illustrate how particle acceleration impacts the interpretation of X-ray data using the X-ray spectra of Kepler's remnant, observed by {\it ASCA} and {\it RXTE}. We show that thermal X-ray emission provides important constraints on the efficiency of particle acceleration, in complement to nonthermal emission. X-ray data from {\it Chandra} and {\it XMM Newton}, plus radio observations, will be essential to quantify nonlinear effects