A new interpretation of the gamma-ray observations of active galactic nuclei

Gamma-ray telescopes have reported some surprising observations of multiTeV photons from distant active galactic nuclei (AGN), which show no significant attenuation due to pair production off the extragalactic background light (EBL). Furthermore, some sources are believed to have such a high intrinsic density of low-energy photons that the very high energy (VHE) photons should have been absorbed near the source. We suggest a new interpretation of these observations, which is consistent with both the leading EBL calculations and the popular AGN models. Ultrahigh-energy cosmic rays with energies below 50 EeV, produced by AGN, can cross cosmological distances and generate secondary photons in their interactions with EBL relatively close to Earth. We calculate the spectrum of the secondary photons and find that it agrees with the γ-ray data. The delays in the proton arrival times can explain the lack of time correlations and the mismatch of the variability time scales inferred from the multiwavelength observations. The gamma-ray data are consistent with the detection of the secondary photons, which has important ramifications for gamma-ray astronomy, cosmic ray physics, EBL, and the intergalactic magnetic fields. Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa, Chiba 2778568, Japan