  Gamma-ray luminosities of some quasar-associated blazars imply jet powers
reaching values comparable to the accretion power even if assuming very strong
Doppler boosting and very high efficiency of gamma-ray production. With much
lower radiative efficiencies of protons than of electrons, and the recent
reports of very strong coupling of electrons with shock-heated protons
indicated by Particle-in-Cell (PIC) simulations, the leptonic models seem to be
strongly favored over the hadronic ones. However, the electron-proton coupling
combined with the ERC (External-Radiation-Compton) models of gamma-ray
production in leptonic models predict extremely hard X-ray spectra, with energy
indices about 0. This is inconsistent with the observed 2-10 keV slopes of
blazars, which cluster around an index value of 0.6. This problem can be
resolved by assuming that electrons can be cooled down radiatively to
non-relativistic energies, or that blazar spectra are entirely dominated by the
SSC (Synchrotron-Self Compton) component up to at least 10 keV. Here, we show
that the required cooling can be sufficiently efficient only at distances r <
0.03pc. SSC spectra, on the other hand, can be produced roughly co-spatially
with the observed synchrotron and ERC components, which are most likely located
roughly at a parsec scale. We show that the dominant SSC component can also be
produced much further than the dominant synchrotron and ERC components, at
distances larger than 10 parsecs. Hence, depending on the spatial distribution
of the energy dissipation along the jet, one may expect to see
gamma-ray/optical events with either correlated or uncorrelated X-rays. In all
cases the number of electron-positron pairs per proton is predicted to be very
low. The direct verification of the proposed SSC scenario requires sensitive
observations in the hard X-ray band which is now possible with the NuSTAR
satellite.
