de Rosa, A.A.de RosaPiro, L.L.PiroNicastro, F.F.NicastroDadina, M.M.DadinaFiore, F.F.Fiore2020-09-172020-09-172001-12-01https://hdl.handle.net/20.500.13025/40X-RAY ASTRONOMY Stellar Endpoints,AGN, and the Diffuse X-ray Background. Edited by Nicholas E. White, Giuseppe Malaguti, and Giorgio G.C. Palumbo. Melville, NY American Institute of Physics, 2001. AIP Conference Proceedings, Volume 599, pp. 610-613 (2001).BeppoSAX has observed two Seyfert 1 galaxies, namely NGC 5548 and NGC 3783, for ~8 days and ~5 days, respectively. The long exposures have provided very high quality spectra. We were able to detect the high energy cut-off in these two sources for the first time. In addition, we observed an emission feature at 0.57 keV, probably due to the OVII Kalpha transition. Flux and spectral variations on time scales of hours and days were observed. A time resolved spectral analysis indicates that this spectral variability is due to a change of the intrinsic power law slope. .Seyfert galaxiesX-ray astronomyX-ray sources (astronomical)astronomical spectraspectral analysis10.1063/1.1434698http://adsabs.harvard.edu/abs/2001AIPC..599..610D2001AIPC..599..610D