1111.0815 (Warren Essey et al.)

On weak redshift dependence of gamma-ray spectra of distant blazars    [PDF]

Warren Essey, Alexander Kusenko

Line-of-sight interactions of cosmic rays provide a natural explanation of
the hard gamma-ray spectra of distant blazars, which are believed to be capable
of producing both gamma rays and cosmic rays. For sources with redshifts z>
0.1, secondary gamma rays produced in cosmic-ray interactions with background
photons close to an observer can dominate over primary gamma-rays originating
at the source. The transition from one component to another is accompanied by a
change in the spectral index depending on the source redshift. We present
theoretical predictions and show that they agree with the data from Fermi Large
Area Telescope. This agreement, combined with the spectral data from
Atmospheric Cherenkov Telescopes, provides evidence of cosmic ray acceleration
by Active Galactic Nuclei and opens new opportunities for studying photon
backgrounds and intergalactic magnetic fields.

View original: http://arxiv.org/abs/1111.0815