  Whatever the ultimate energy source of gamma-ray bursts turns out to be, the
resulting sequence of physical events is likely to lead to a fairly generic,
almost unavoidable scenario: a relativistic fireball that dissipates its energy
after it has become optically thin. This is expected both for cosmological and
halo distances. Here we explore the observational motivation of this scenario,
and the consequences of the resulting models for the photon production in
different wavebands, the energetics and the time structure of classical
gamma-ray bursters.
