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