PoS - Proceedings of Science
Volume 301 - 35th International Cosmic Ray Conference (ICRC2017) - Session Gamma-Ray Astronomy. GA-extra-galactic
Measurement of the EBL through a combined likelihood analysis of gamma-ray observations of blazars with the MAGIC telescopes
A. Moralejo*, A. Dominguez, V. Fallah Ramazani, T. Hassan, D. Mazin, M. Nievas Rosillo, E. Prandini, J. Sitarek, G. Vanzo, M. Vazquez Acosta  on behalf of the MAGIC collaboration
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Pre-published on: August 16, 2017
Published on: August 03, 2018
The extragalactic background light (EBL) is the radiation accumulated through the history of the
Universe in the wavelength range from the ultraviolet to the far infrared. Local foregrounds make
the direct measurement of the diffuse EBL notoriously difficult, while robust lower limits have
been obtained by adding up the contributions of all the discrete sources resolved in deep infrared
and optical galaxy observations. Gamma-ray astronomy has emerged in the past few years as a
powerful tool for the study of the EBL: very-high-energy (VHE) photons traversing cosmological
distances can interact with EBL photons to produce e+e- pairs, resulting in an energy-dependent
depletion of the gamma-ray flux of distant sources that can be used to set constraints on the EBL
density. The study of the EBL is one of the key scientific programs currently carried out by the
MAGIC collaboration. We present here the results of the analysis of 32 VHE spectra of 12 blazars
in the redshift range 0.03 - 0.94, obtained with over 300 hours of observations with the MAGIC
telescopes between 2010 and 2016. A combined likelihood maximization approach is used to
evaluate the density and spectrum of the EBL most consistent with the MAGIC observations.
The results are compatible with state-of-the-art EBL models, and constrain the EBL density to be
within ' 20% the nominal value in such models. The study reveals no anomalies in gamma-ray
propagation in the large optical depth regime - contrary to some claims based on meta-analyses
of published VHE spectra.
DOI: https://doi.org/10.22323/1.301.0604
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