The downward X-ray spectrum of PKS 2155-304 in the inner jet description

The compact radio source PKS 2155-304 ( z=0.116) is a gamma-ray blazar and one of the brightest in UV and X-ray bands, repeatedly monitored at X-ray frequencies in the past years, and observed recently by Chandra and XMM-Newton. Various intensity states and a continuously downward-curved trend with the energy is displayed clearly, summarizing some of this broadband X-ray spectral energy distributions. A synchrotron self-Compton (in-jet) model, with a single emitting region, accounts well for the multiwavelength behaviour of this blazar.