Revisiting the Indication for a low opacity Universe for very high energy gamma-rays
arXiv:1211.6405
Abstract
Very high energy (VHE, energy >~ 100 GeV) γ-rays undergo pair production with photons of the extragalactic background light (EBL). Thus, the intrinsic γ-ray flux of cosmological sources is attenuated and the Universe should be opaque to γ-rays above a redshift dependent energy. Recently, an indication has been found that the Universe is more transparent than predicted by a lower-limit EBL model. Here, this indication is confronted with additional VHE γ-ray spectra and different EBL models. Depending on the model for the opacity, the indication persist between a ~2.6 σ and ~4.3 σ confidence level.
Contributed to the 8th Patras Workshop on Axions, WIMPs and WISPs, Chicago, July 18-22, 2012, added further discussion and references for cascade emission, main conclusion unchanged