Cosmic gamma-ray bursts

The results of the observation of cosmic gamma-ray bursts are discussed and available theoretical models are presented. Emphasis is placed on a cosmological model in which a gamma burst results from a powerful (≈ 10⁵¹–10⁵³ erg) and very short ( ≈10 –100 s) energy release which occurs in a compact ( ≈ 10⁶–10⁷ cm) region and gives rise to a photon–lepton fireball expanding at an ultrarelativistic velocity (Lorentz-factor Γ ≥ 100). The interaction of the relativistic shock wave with its environment produces the observed X-ray and optical afterglows of a burst. Possible physical models of such an energy release event are discussed and some related problems considered.