Modelling the rapid variability of Blazar emission

A homogeneous, synchro-Compton model (SSC) of the spectra of gamma-ray emitting blazars is discussed in which, in a single emission region, electrons emit synchrotron photons and scatter them to high (gamma-ray) energy. In contrast to previous work, the full time-dependent evolution of the electron and photon spectra are followed, assuming a power-law for the electron injection. The predictions of the model with regard to variability of the source are calculated and applied to the object Mkn 421, which displayed rapid variability in its X-ray and TeV emission during a multi-wavelength campaign in 1994. By fitting first the observed quiescent spectrum over all 18 orders of magnitude in frequency, it is shown that the time dependence of the keV/TeV flare could have been the result of a sudden increase in the maximum energy of the injected electrons. We also present solutions showing that the behaviour of the emission is qualitatively different when external photons are used as the targets for inverse Compton scattering, indicating that the targets during the 1994 TeV flare of Mkn 421 are more likely to have been of synchro-Compton origin.