BEPPOSAX OBSERVATION OF THE X-RAY-EMISSION OF GAMMA-RAY BURSTS

For more than 20 years the difficulty, to locate the direction of a be am, intrinsic to the gamma ray detection techniques, and the rapidity of the phenomenon itself has been the insurmountable limit to the asso ciation of Gamma-Ray Bursts with an already established class of sourc es. The combination of different instruments aboard BeppoSAX has turne d out to be a real breakthrough for the study of this outstanding phen omenon. From January to May; 1997 four gamma ray bursts were detected with Wide Field Instruments and a rapidly pointed with Narrow Field In struments. In the direction of three of these burst (and likely also o f the fourth one) faint, fading sources, have been found. These fading sources decay according to a power law but with the evidence of a fla ring activity. The spectra are hard and non-thermal. Some data suggest that the burst itself continuously evolves into the decaying source a nd the energy associated to the source is comparable to that of the bu rst itself. This discovery, followed by the detection of optical trans ients associated with two of the X-ray sources, one with a nebulosity ad another with redshifted absorption features and a scintillating rad io source. has substantially enriched the phenomenological landscape o f orders of magnitude in wavelength, positioning and time starting a n ew season of theoretical interpretations. The perspectives of this res earch of BeppoSAX and the new contribution of other missions, with par ticular regard to RossiXTE, are also discussed.