Constraining Emission Models of Luminous Blazar Sources
  Many luminous blazars which are associated with quasar-type active galactic
nuclei display broad-band spectra characterized by a large luminosity ratio of
their high-energy (gamma-ray) and low-energy (synchrotron) spectral components.
This large ratio, reaching values up to 100, challenges the standard
synchrotron self-Compton models by means of substantial departures from the
minimum power condition. Luminous blazars have also typically very hard X-ray
spectra, and those in turn seem to challenge hadronic scenarios for the high
energy blazar emission. As shown in this paper, no such problems are faced by
the models which involve Comptonization of radiation provided by a broad
line-region, or dusty molecular torus. The lack or weakness of bulk Compton and
Klein-Nishina features indicated by the presently available data favors
production of gamma-rays via up-scattering of infrared photons from hot dust.
This implies that the blazar emission zone is located at parsec-scale distances
from the nucleus, and as such is possibly associated with the extended,
quasi-stationary reconfinement shocks formed in relativistic outflows. This
scenario predicts characteristic timescales for flux changes in luminous
blazars to be days/weeks, consistent with the variability patterns observed in
such systems at infrared, optical and gamma-ray frequencies. We also propose
that the parsec-scale blazar activity can be occasionally accompanied by
dissipative events taking place at sub-parsec distances and powered by internal
shocks and/or reconnection of magnetic fields. These could account for the
multiwavelength intra-day flares occasionally observed in powerful blazars
sources.
