Intensity and possible structure of optical emission of supernova remnants in the radiative stage of their evolution

It is shown that the optical emission of a supernova remnant expanding through the gas of 0.2-1 sm-3 density should exceed the night-sky background if the expanding velocity v sub(s)>50-60 km/s. The emission originates from both thin, nearly homogeneous envelope formed by the blast wave and a system of faint filaments which according to Pikel'ner (1973) mechanism result from intersection of shock waves, diversely refracted by the discontinuties of interstellar medium. The value b sub(s) can be estimated from Doppler shifts of lines of the quasihomogeneous envelope or from velocities of the most faint filaments which are approach v sub(s) asymptotically