The 0.1-200 keV spectrum of the blazar PKS 2005-489 during an active state

The bright BL Lac object PKS 2005-439 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 st ate 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 in the model assumptions.