Circumstellar Interaction

Abstract

In this chapter presents an introduction to hydrodynamic and radiative interactions of supernovae with circumstellar matter (CSM), primarily in the context of core-collapse supernovae. Hydrodynamic interaction between the supernova ejecta and CSM produced by a wind from the progenitor star leads to a forward shock that accelerates and heats the inner layers of the CSM, a reverse shock that reheats the outer layers of the ejecta, and a thin interaction region (ideally a contact discontinuity) between the two, where the formation of a cool dense shell and Rayleigh-Taylor instabilities are expected. The hot shocked layers of the ejecta and the CSM may emit optical, ultraviolet, and X-ray radiation. Owing to radiative interactions, the cooler unshocked regions also may emit in these spectral ranges. Particle acceleration and magnetic-field amplification in the interaction region can result in synchrotron radio emission. Supernova irradiation destroys dust grains in the inner layers of the CSM, but in the outer layers surviving dust may absorb supernova radiation and re-emit in the infrared. Complications are clumping in the CSM, shells of CSM resulting from episodic presupernova ejections of matter, and optically-thick CSM. This chapter briefly presents evidence for CSM of Type Ia supernovae, which is more elusive and tends to be manifested in different ways; Chapter 21 gives more details.