On conservative models of "the pair-production anomaly" in blazar spectra at Very High Energies

Abstract

For some blazars, the gamma-ray absorption features due to pair-production on the Extragalactic Background Light (EBL) are fainter than expected. The present work reviews the main models that could explain this paradox, with emphasis on conservative ones, that do not include any new physics. The models that are intrinsic to the source, do allow a very hard primary spectrum, but fail to explain a regular redshift dependence of the anomaly starting energy. The model that includes a contribution from secondary photons produced by cosmic rays (CR) near the Earth seems to require a well collimated CR beam, what is hard to achieve. Finally, the model with secondary photons produced in electromagnetic (EM) cascades initiated by primary gamma-rays is considered. In principle, it allows to decrease the statistical significance of the anomaly and, while requiring quite low EGMF strength B, does not contradict to most contemporary constraints on the B value. Additionally, it is shown that the recently observed correlation between directions to hard gamma-ray sources and voids in the Large Scale Structure is a natural feature of the EM cascade model.

8 pages, 4 figures. This paper tries to summarize the status of the field by the end of January, 2015. In v. 2 several typos were corrected

References in corpus (9)

• The Imprint of The Extragalactic Background Light in the Gamma-Ray Spectra of Blazars
• Hints of the existence of Axion-Like-Particles from the gamma-ray spectra of cosmological sources
• Formation of hard VHE gamma-ray spectra of blazars due to internal photon-photon absorption
• Signatures of axion-like particles in the spectra of TeV gamma-ray sources
• Search for Extended γ-ray Emission around AGN with H.E.S.S. and Fermi-LAT
• Cascading on extragalactic background light
• A Correlation Between Hard Gamma-ray Sources and Cosmic Voids Along the Line of Sight
• Diffuse Extragalactic Background Radiation
• Synchrotron pair halo and echo emission from blazars in the cosmic web: application to extreme TeV blazars

Cited by in corpus (6)

• Electromagnetic cascade masquerade: a way to mimic $\gamma$--axion-like particle mixing effects in blazar spectra
• Lorentz Invariance Violation Effects on Gamma-Gamma Absorption and Compton Scattering
• Expected Signature For the Lorentz Invariance Violation Effects on $\gamma -\gamma$ Absorption
• Observable spectral and angular distributions of $\gamma$-rays from extragalactic ultrahigh energy cosmic ray accelerators: the case of extreme TeV blazars
• Testing models of extragalactic $\gamma$-ray propagation using observations of extreme blazars in GeV and TeV energy ranges
• The VHE anomaly in blazar spectra and related phenomena