Аннотация:Gamma-ray burst afterglows are believed to be described reasonably by synchrotron emission from relativistic blast waves at cosmological distances. We perform a detailed calculation using a full angle-, time- and frequency-dependent transfer equation and taking into account the effect of synchrotron self-absorption. The method developed for solving the transfer equation can be applied to the motion of a fluid with a Lorentz factor of up to 1000. We consider emission from the whole region behind the shock front and use the Blandford-McKee self-similar solution to describe the fluid behind the shock. We calculate the spectra and the light curves from a power-law distribution of electrons in an expanding relativistic shock and compare them with theoretical estimations.