Transition of the light velocity in the Vavilov-Cerenkov effect

Accelerated and decelerated motions of a. charged point particle inside medium are studied. It is shown explicitly that in addition to the bremsstrahlung and Cerenkov singular waves: previously unknown electromagnetic singular wave should be observed. It arises when the charge velocity coincides with the light velocity in medium. This wave has the same singularity as the Cerenkov one and, therefore, it is more singular than the bremsstrahlung wave. The spacetime regions where these waves exist and conditions under which they appear are determined.