X-Ray Emission Properties of Supernova Remnants

X-ray emission from supernova remnants can be broadly divided into thermal X-ray emission from the shock-heated plasmas and in nonthermal (synchrotron) emission caused by very high-energy (10–100 TeV) electrons moving in the magnetic fields of the hot plasmas. The thermal X-ray emission of young supernova remnants is often dominated by line emission from alpha-elements (O, Ne, Mg, Si, S, Ar, Ca) and iron-group elements. X-ray imaging spectroscopy is therefore an invaluable tool to measure the elemental composition of the supernova ejecta and its spatial distribution. In addition, thermal X-ray emission provides important plasma diagnostics, such as the plasma electron temperatures and the densities. The plasma is often out of ionization equilibrium, as a result of the low densities and young ages of the supernova remnants. The ionization nonequilibrium is characterized by the ionization age parameter or n e t. The ionization age and the emission measure can both be used to also estimate the plasma densities. X-ray synchrotron radiation, which in the youngest remnants is emitted from narrow filaments, provides important clues about the cosmic-ray acceleration properties and magnetic field strengths and turbulence near supernova remnant shock fronts.