  Spectra of the brightest blazars detected by the Fermi Gamma-ray Space
Telescope Large Area Telescope cannot be described by a simple power law model.
A much better description is obtained with a broken power law, with the break
energies of a few GeV. We show here that the sharpness and the position of the
breaks can be well reproduced by absorption of gamma-rays via photon--photon
pair production on HeII Lyman recombination continuum and lines. This implies
that the blazar zone lies inside the region of the highest ionization of the
broad-line region (BLR) within a light-year from a super-massive black hole.
The observations of gamma-ray spectral breaks open a way of studying the BLR
photon field in the extreme-UV/soft X-rays, which are otherwise hidden from our
view.
