Tagliaferri, G.G.TagliaferriGhisellini, G.G.GhiselliniGiommi, P.P.GiommiCelotti, A.A.CelottiChiaberge, M.M.ChiabergeChiappetti, L.L.ChiappettiGlass, I. S.I. S.GlassMaraschi, L.L.MaraschiTavecchio, F.F.TavecchioTreves, A.A.TrevesWolter, A.A.Wolter2020-09-172020-09-172001-03-01https://hdl.handle.net/20.500.13025/16Astronomy and Astrophysics, v.368, p.38-43 (2001)The bright BL Lac object PKS 2005-489 was observed by BeppoSAX on November 1-2, 1998, following an active X-ray state detected by RossiXTE. The source, detected between 0.1 and 200 keV, was in a very high state with a continuum well fitted by a steepening spectrum due to synchrotron emission only. Our X-ray spectrum is the flattest ever observed for this source. The different X-ray spectral slopes and fluxes, as measured by various satellites, are consistent with relatively little changes of the peak frequency of the synchrotron emission, always located below 10^17 Hz. We discuss these results in the framework of synchrotron self-Compton models. We found that for the BeppoSAX observation, the synchrotron peak frequency is between 10^15^ and 2.5 10^16 Hz, depending on the model assumptions.BL Lacertae objects: generalX-rays: galaxiesBL Lacertae objects: individual: PKS 2005-489Astrophysicsjournal article10.1051/0004-6361 20010011http://adsabs.harvard.edu/abs/2001A&A...368...38T2001A&A...368...38T