[en] The analytic solution of equations for the evolution of supernova remnants in the radiative phase is found. It shows that the X-ray source Cygnus Superbubble might be formed by an explosion with the energy release 10₅₂-10₅₃ erg. The analysis of the light curve of SN 1961 shows that this supernova in the result of an explosion with energy about 2x10₅₂ erg in a supermassive star with the mass of order 10₃M * where M* is the solar mass. An evolutionary sequence for the formation of giant shell sources is suggested: presupernova - an object of the type R136a, supernova - an explosion of the type SN 1961 and the supernova remnant - a source of the type Cygnus Superbubble