X-ray afterglow of gamma-ray bursts

In almost three years BeppoSAX has detected 27 gamma-ray bursts with the Wide Field Cameras. The majority have been localized in a short time and observed with the Narrow Field Instruments. More bursts detected by various satellite experiments or by the Interplanetary Network have been followed up by X-ray Telescopes, including SAX itself. Around 15 afterglow sources have been unambiguously detected and studied. Several features have been interpreted in the framework of synchrotron shocks in fireballs, but not all the data may be interpreted in terms of this simplified approach. I discuss the relevance of X-ray afterglow data to answer some open questions.