In most of the scenarios currently considered, the progenitor is a black hole recently formed, surrounded by an accretion disk. This black hole can result from the collapse of a very massive star in fast rotation (hypernova model) or from the collapse of two neutron stars (merger model). The matter is ejected in both cases with an ultra relativistic speed (Lorentz factor larger than 100) in a cone whose opening is of a few degrees, the observer being placed by chance in a direction included in this cone. Various matter shells are ejected with different speeds. When a shell meets another one, there is an internal shock. The electrons accelerated by this shock radiate, probably by synchrotron radiation in the existing magnetic fields, and produce gamma rays (emission which has given the name to the phenomenon), but also X rays and visible light (prompt emission). Several internal shocks can take place, which accounts for the complexity and the variety of the GRB phenomenon. Finally the shells collide with the surrounding matter, which can be the interstellar environment or the material expelled previously by the progenitor. A radiation, probably due to the synchrotron emission, is then produced, covering all the electromagnetic spectrum from X rays to the radio waves (afterglow emission).

These scenarios have been confirmed by several observations: