Cosmic Čerenkov emission

In real intensive cosmic sources it is necessary to take into account the ?erenkov reabsorption which restricts the brightness temperature of ?erenkov emission by energies of emitted relativistic electrons. As ?erenkov optical depth is given by τ_c~N/E, the brightness temperature of emission on frequencies near gyrofrequency is determined by electron energyE _r in which τ_c(E _r)=1. It is shown that most of the synchrotron sources (quasars, pulsars) must be powerful sources of ?erenkov emission. In these sources the high density of low frequency ?erenkov emission can give rise to many parametric effects.