Evidence for a cosmological effect in \gamma-ray spectra of BL Lacs

TL;DR

This paper investigates spectral breaks in BL Lac gamma-ray spectra, analyzing their dependence on distance and EBL absorption, using updated catalogs and a novel Bayesian model to constrain EBL effects.

Contribution

It introduces a new Bayesian approach to analyze gamma-ray spectral breaks and provides updated constraints on the extragalactic background light's impact.

Findings

Spectral breaks depend on source distance.

The Bayesian model constrains EBL-induced absorption.

Results support the presence of a cosmological effect in gamma-ray spectra.

Abstract

We update the list of GeV-TeV extragalactic \gamma-ray sources using the 2-year catalog from the Fermi-LAT and recent results ground-based \gamma-ray telescopes. Breaks in the spectra between the high energy (100 MeV <E< 300 GeV) and the very high energy (E> 200 GeV) ranges, and their dependence on distance, are discussed in the context of absorption on the extragalactic background light (EBL). We calculate the size of the expected break using a model for the EBL and compare it to the data taking into account systematic uncertainties in the measurements. We develop a novel Bayeasian model to describe this dataset and use it to constrain two simple models for the EBL-induced breaks.