http://arxiv.org/abs/1609.01013
Most of the studies on extragalactic {\gamma}-ray propagation performed up to now only accounted for primary gamma-ray absorption and adiabatic losses (absorption-only model). However, there is growing evidence that this model is oversimplified and must be modified in some way. (…) There are many hints that a secondary component from electromagnetic cascades initiated by primary $\gamma$-rays or nuclei may be observed in the spectra of some blazars. We study the impact of electromagnetic cascades from primary $\gamma$-rays or protons on the physical interpretation of blazar spectra obtained with imaging Cherenkov telescopes. We use the publicly-available code ELMAG to compute observable spectra of electromagnetic cascades from primary $\gamma$-rays. For the case of primary proton, we develop a simple, fast, and reasonably accurate hybrid method to calculate the observable spectrum. (…) Electromagnetic cascades show at least two very distinct regimes labeled by the energy of the primary $\gamma$-ray ($E_{0}): the one-generation regime for the case of $E_{0}$ <10 TeV and the universal regime for $E_{0}$ >100 TeV and redshift to the source $z_{s}$>0.02. (…) In the framework of the intermediate hadronic model, the observable spectrum depends only slightly on the primary proton energy, but it strongly depends on z c at E>500 GeV. As a rule, both electromagnetic and hadronic cascade models provide acceptable fits to the observed SEDs. We show that the best-fit model intensity in the multi-TeV region of the spectrum in the framework of the electromagnetic cascade model is typically greater than the one for the case of the absorption-only model. Finally, for the case of blazar 1ES 0229+200 we provide strong constraints on the intermediate hadronic model (…).
T. Dzhatdoev, E. Khalikov, A. Kircheva, et. al.
Tue, 6 Sep 16
61/74
Comments: 24 pages, 31 figures, abstract above shortened
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