Fermi observations of blazars and constraints on the location of the
gamma-ray emission region

The Large Area Telescope of the Fermi observatory has detected
hundreds of AGNs, most of them are blazars. The GeV spectra of the
flat spectra radio quasars were claimed to be inconsistent with a
simple power law model or any smoothly curved models. Instead, a much
better description was obtained with a broken power law, with the
break energies of a few GeV. The sharpness and the position of the
breaks could be well reproduced by absorption of gamma-rays via
photon-photon pair production on He II and H I Lyman recombination
continuum (LyC) and lines. In addition to the spectra from individual
sources, we have created stacked redshift-corrected spectrum of
several bright blazars. This spectrum shows a strong break at 20 GeV
associated with hydrogen LyC. The detected breaks univocally prove
that the gamma-ray emitting region lies with the BLR. This solves the
long-standing question of the location of the gamma-ray production
region.