Montanari, E.E.MontanariAmati, L.L.AmatiFrontera, F.F.FronteraCapalbi, MilviaMilviaCapalbi2020-09-172020-09-172001-01-01https://hdl.handle.net/20.500.13025/108Gamma-Ray Bursts in the Afterglow Era Proceedings of the International Workshop Held in Rome, Italy, 17-20 October 2000, ESO ASTROPHYSICS SYMPOSIA. ISBN 3-540-42771-6. Edited by E. Costa, F. Frontera, and J. Hjorth. Springer-Verlag, 2001, p. 195We present preliminary results of the analysis of BeppoSAX data of GRB 990806. The high energy spectrum of the prompt event is fitted by a single powerlaw whose spectral index does not vary significantly. In the error box of the GRB, determined by the WFC, the BSAX NFI have detected a previously unknown X-ray source. Based on the power-law temporal decay of its flux in the 2-10 keV range, f(t) ˜ t^{-1.15}, the source has been identified with the GRB afterglow.10.1007/10853853_53http://adsabs.harvard.edu/abs/2001grba.conf..195M2001grba.conf..195M