In this paper we extend our approach to modeling multifrequency emission variability from blazars to include external-radiation Compton ( ERC ) emission and electron energy losses from inverse Compton scattering of seed photons originating outside the jet .
We consider seed-photon emission from a dusty molecular torus and the broad line region ( BLR ) surrounding the central engine .
We establish constraints on the properties of the molecular torus and BLR under which synchrotron self-Compton ( SSC ) emission dominates such that the results obtained in our previous paper are applicable .
The focus of this study is on relative time delays between the light curves observed at different frequencies .
For definiteness , we consider emission resulting from a collision between relativistic shocks , but the results apply more generally to conditions involving acceleration of relativistic electrons and/or magnetic field amplification at any type of front .
Unlike SSC emission , ERC flares involving a constant field of seed photons are not delayed by light travel time of the seed photons .
The main cause of delays is from radiative energy losses , which result in frequency stratification behind the front and quench the flare first at the highest frequencies , progressing to lower frequencies as time advances .
However , if the spectrum of electrons injected at the shock front is characterized by a relatively high value of the minimum energy ( a Lorentz factor \gamma _ { { { } } min } \sim 100 is sufficient ) , the ERC flare in the X-ray band can be delayed and may even peak after the injection has ceased .
This effect is strongly frequency dependent , with a longer lag at lower frequencies and an X-ray spectral index that changes rapidly from positive ( inverted spectrum ) to steep values .