Gamma-rays from Blazars and the Extragalactic Background Light

Abstract

Recent observations of blazars at high energy (HE, 0.1-100 GeV) and very high energy (VHE, >0.1 TeV) have provided important constraints on the intensity and spectrum of the diffuse Extragalactic Background Light (EBL), shedding light on its main origin. Several issues remain open, however, in particular in the mid- and far-infrared bands and in the blazar emission at multi-TeV energies. This review summarizes the observational and theoretical progress in the study of the EBL with gamma-rays and the most promising future improvements, which are mainly expected from spectra in the multi-TeV range.

Invited review for International Journal of Modern Physics D, 30 pages, 9 figures

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• Axion-like particles and the propagation of gamma rays over astronomical distances
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• Exploring the Active Galactic Nuclei population with extreme X-ray to optical flux ratios (Fx/Fo >50)
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• Aspects of astrophysical particle production and beyond the Standard Model phenomenology