Revisiting the Indication for a low opacity Universe for very high energy gamma-rays

Abstract

Very high energy (VHE, energy >~ 100 GeV) {\gamma}-rays undergo pair production with photons of the extragalactic background light (EBL). Thus, the intrinsic {\gamma}-ray flux of cosmological sources is attenuated and the Universe should be opaque to {\gamma}-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 {\gamma}-ray spectra and different EBL models. Depending on the model for the opacity, the indication persist between a ~2.6 {\sigma} and ~4.3 {\sigma} confidence level.