  Blazar flare data show energy-dependent lags and correlated variability
between optical/X-ray and GeV-TeV energies, and follow characteristic
trajectories when plotted in the spectral-index/flux plane. This behavior is
qualitatively explained if nonthermal electrons are injected over a finite time
interval in the comoving plasma frame and cool by radiative processes.
Numerical results are presented which show the importance of the effects of
synchrotron self-Compton cooling and plasmoid deceleration. The use of INTEGRAL
to advance our understanding of these systems is discussed.
