Professor Umran S. Inan

Winter 1997-98

Date: Wednesday, February 18, 1998

Time: 4:15 PM Refreshments at 4:00

Location: Gesb 124 (Green Earth Sciences Bldg.)

The Mystery of Cosmic Gamma-Ray Bursts Resolved

Prof. Vahe Petrosian

Applied Physics

Stanford University


For about thirty years the gamma-ray bursts, GRBs for short, have puzzled the astrophysicists as to their location, origin, energy source and radiation processes. GRBs first were detected by Vela satelites which were put in orbit to moniter the existing nuclear test ban treaties. These sources are characterized by short (<1000s), highly variable (time scale about 0.001s) and intense emission of gamma-rays (tens of KeV to GeV photons). The short time scale indicate association with object equal to or smaller than a neutron star (about 10km). But because of their short durations discovery of counterparts at other wavelengths has been proven difficult. Consequently, there has been models putting them at distances ranging from inside the solar system to large cosmological distances, with a lengthy and serious debate whether these are sources located in our galaxy or are some unknown extrgalactic objects. However, new observations, mostly less than a year old, appear to be on the verge of resolving this issue in favor of the cosmological hypothesis. This does not completly solve the basic problem of the origin of the GRBs. It makes them much more interesting and enigmatic because now they most likely are the highest luminosity sources detected so far, emitting most of their energy at highest photon energies. Some old and new ideas about their energy source and radiation mechanism will be described.