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Session 45 - The Structure and Evolution of The Universe - II.
Topical, Oral session, Tuesday, June 09
Presidio,
The enigma of gamma-ray bursts is beginning to unravel, under the impact of superb recent discoveries from CGRO, Beppo-SAX, HST, ASCA, RXTE and ground-based observations of afterglows at X-ray, optical and radio wavelengths, as well as recent reports of distance measurements which place them at cosmological distances. The energy release inferred in these outbursts rivals that of supernovae, while its photon energy output rate may even exceed it. Most of the emitted photon energy is concentrated in the early gamma-ray and X-ray phases in the first tens of seconds, followed by a characteristic decay at increasingly softer wavelengths over timescales extending to months. Current models envisage this to be the outcome of a cataclysmic stellar event leading to a relativistically expanding fireball, in which particles are accelerated at shocks and produce nonthermal radiation. We review the rich observational evidence as well as the puzzles faced by theoretical models, and discuss the impact of future space observations in addressing these challenges.
