SSC radiation in BL Lac sources, the end of the tether
  The synchrotron-self Compton (SSC) radiation process is widely held to
provide a close representation of the double peaked spectral energy
distributions from BL Lac Objects (BL Lacs), which are marked by non-thermal
beamed radiations, highly variable on timescales of days or less. Their
outbursts in the gamma ray relative to the optical/X rays might be surmised to
be enhanced in BL Lacs as these photons are upscattered via the inverse Compton
(IC) process. From the observed correlations among the spectral parameters
during optical/X-ray variations we aim at predicting corresponding correlations
in the gamma-ray band, and the actual relations between the gamma-ray and the
X-ray variability consistent with the SSC emission process. We start from the
homogeneous single-zone SSC source model, with log-parabolic energies
distributions of emitting electron as required by the X-ray data of many
sources. We find relations among spectral parameters of the IC radiation in
both the Thomson (for Low energy BL Lacs) and the Klein-Nishina regimes (mainly
for High energy BL Lacs) and we compute how variability is driven by a smooth
increase of key source parameters, primarily the root mean square electron
energy. The single component SSC source model in the Thomson regime turns out
to be adequate for many LBL sources. However, the simple model meets its limits
with the fast/strong flares recently reported for a few sources in the TeV
range; these require sudden accelerations of emitting electrons in a second
source component.
