BeppoSAX observation of the X-ray emission of Gamma-Ray Bursts

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