  As a key process that refreshes the interstellar medium, the dynamics and
radiative properties of the supernova remnant (SNR) expansion front not only
reflect the physical environment of the old interstellar medium (ISM)
surrounding the supernova, but they also provide information about the
refreshed ISM. However the expansion dynamics of SNRs cannot be simply
explained by the conventional law of spherical shock wave propagation; on the
other hand, the high energy radiation requires an additional electron
acceleration mechanism in the shock front beyond thermal collision. We consider
herein the detonation wave description of the SNR expansion, in which magnetic
reconnection follows the shock front and transfers the SNR magnetic field
energy to both fluid thermal energy and particle kinetic energy. The structure
of the magnetic reconnection detonation (MRD) is identified based on scaling
analysis in this paper. By applying the MRD description of the SNR expansion
shock to the example of the Crab Nebula, this paper shows that the MRD
description can explain both the accelerative expansion of the nebula as well
as the origin of the luminous expanding shell.
