1999A&AS..138..533M

The discovery of X-ray, optical and radio afterglows of GRBs provides an important tool for understanding these sources. Most current models envisage GRB as arising in a cataclysmic stellar event leading to a relativistically expanding fireball, where particle acceleration at shocks lead to nonthermal radiation. The predictions of this scenario are in substantial agreement with the bulk of the observations. In addition, the data show a diversity of finer structure behavior, which is providing constraints for more detailed models. Current issues of interest are the implications of the beaming for the energetics, the afterglow time structure, dependence on progenitor system, and the role of the environment.