Intrinsic absorption in 3C 279 at GeV-TeV energies and consequences for   estimates of the EBL
  We revisit the limits of the level of the extragalactic background light (EBL) recently reported by the MAGIC collaboration based on the observed gamma-ray spectrum of the quasar 3C279, considering the impact of absorption of high-energy gamma-ray photons inside the broad line region (BLR) of the quasar. We use the photoionization code CLOUDY to calculate the expected optical-UV radiation field inside the BLR and the optical depth to gamma-rays for a relatively extended set of the parameters. We found that the absorption of gamma-ray photons, though important for the estimate of the true radiative output of the source, does not produce an important hardening of the spectrum of 3C279 in the energy band accessible by MAGIC, supporting the method used to infer the upper limits to the level of the EBL. 
F. Tavecchio, D. Mazin