A new similarity solution for reverse shocks in supernova remnants

A new self-similar solution to the early time development of an adiabatic reverse shock in initially uniform supernova ejecta is presented. The solution is obtained by treating the reverse shock as an infinitely thin, freely expanding shell. The solution is in satisfactory agreement with hydrodynamic simulations. The solution may provide a better approximation to the shell structure at early times than those simulations, because of the finite gridding of the latter and the large density and temperature gradients in the shell. It is much simpler to use than hydrodynamic simulations. The solution may also have some application to the reverse shock structure in freely expanding clumps of ejecta.