The evolution of supernova remnants as radio sources

The acceleration of relativistic electrons by hydromagnetic turbulence in shell-type supernova remnants (SNRs) is examined in relation to their structural development through interaction with the interstellar medium. The transport equation governing the energy spectrum of the electrons is analytically solved, enabling study of the evolution of their synchrotron radio emission. The sudden emergence of SNRs as long-lived radio sources, several decades after the supernova event, is then explained. Their subsequent radio evolution, with spectral changes and structural details as exemplified by the young remnant Cassiopeia A, follows naturally. (author)