Synchrotron and Compton Components and their Variability in BL Lac   Objects
  BL Lacertae objects are extreme extragalactic sources characterized by the emission of strong and rapidly variable nonthermal radiation over the entire electromagnetic spectrum. Synchrotron emission followed by inverse Compton scattering in a relativistic beaming scenario is generally thought to be the mechanism powering these objects. ... 
P.Giommi, G. Ghisellini, P. Padovani, and G. Tagliaferri