Supernova Remnants at High Energy

Many shell supernova remnants are now known to radiate synchrotron X-rays. Several objects have also been detected in TeV gamma rays. Nonthermal X-rays and gamma rays can be produced in shell remnants by extremely energetic ions and electrons due to decay of π⁰ mesons produced in inelastic collisions between ions and thermal gas, or by electron synchrotron, bremsstrahlung, or inverse-Compton radiation. Thus observations at X-ray and gamma-ray wavelengths constrain the process of particle acceleration to high energies in the shock waves of supernova remnants. This review examines the relevant characteristics of Type Ia and core-collapse supernovae, the dynamics of their evolution through the Sedov blast-wave phase, the basic physics of diffusive shock acceleration, and the physics of the relevant radiative processes. It also reviews the current status of observations of shell remnants from X-rays to TeV gamma rays, and summarizes what we can learn about particle acceleration.