Time dependent spectra of Blazars
  We calculate the time dependent electron distribution under the assumption of continuous injection of new relativistic particles, and assuming radiative cooling (by sinchrotron and inverse Compton) and particle escape. Resulting photon spectra are calculated taking into account the time delays introduced by the different light travel times across the source. We apply these calculations to the varying X-ray spectrum of Mkn 421. 
Marco Chiaberge, Gabriele Ghisellini