Supernova remnants on the stage when preshock pressure is not small : a new adiabatic stage and enlargement of envelope relative thickness.

A model is proposed for simulating a supernova remnant at the counterpressure stage, which replaces the radiative stage. The luminescence regime is replaced by one close to the adiabatic regime, and the envelope's relative thickness L begins to increase. It is hypothesized that the number of supernova remnants is distributed according to their relative thickness. The distribution of the sources observed shows an increase in their number with an increase in L, in quantitative agreement with theory.