On the transition of the adiabatic supernova remnant to the radiative   stage in a nonuniform interstellar medium
  Methods for estimation of different reference times which appear in the description of transition of a strong adiabatic shock into the radiative era are reviewed. The need for consideration of an additional transition subphase in between the end of the adiabatic era and the beginning of the radiative ''pressure-driven snowplow'' stage for a shock running in the uniform or nonuniform medium is emphasized. This could be of importance in particular for studying the interaction of supernova remnants (SNRs) with molecular clouds and therefore for understanding the processes of the cosmic ray production in such systems. The duration of this subphase - about 70% of SNR age at its beginning - is almost independent of the density gradient for media with increasing density and is longer for higher supernova explosion energy and for smaller density in the place of explosion. It is shown as well that if the density of the ambient medium decreases then the cooling processes could differ from the commonly accepted scenario of the ''thin dense radiative shell'' formation. This property should be studied in the future because it is important for models of nonspherical SNRs which could be only partially radiative. 
O.Petruk (Institute for Applied Problems in Mechanics and Mathematics)