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Active galactic nuclei (AGN) can produce both gamma rays and cosmic rays. Theobserved high-energy gamma-ray signals from distant blazars may be dominated bysecondary gamma rays produced along the line of sight by the interactions ofcosmic-ray protons with background photons. This explains the surprisingly lowattenuation observed for distant blazars, because the production of secondarygamma rays occurs, on average, much closer to Earth than the distance to thesource. Thus the observed spectrum in the TeV range does not depend on theintrinsic gamma-ray spectrum, while it depends on the output of the source incosmic rays. We apply this hypothesis to a number of sources and, in everycase, we obtain an excellent fit, strengthening the interpretation of theobserved spectra as being due to secondary gamma rays. We explore theramifications of this interpretation for limits on the extragalactic backgroundlight and for the production of cosmic rays in AGN. We also make predictionsfor the neutrino signals, which can help probe acceleration of cosmic rays inAGN.

Role of line-of-sight cosmic ray interactions in forming the spectra of distant blazars in TeV gamma rays and high-energy neutrinos