FERMI LARGE AREA TELESCOPE CONSTRAINTS ON THE GAMMA-RAY OPACITY OF THE UNIVERSE
Abdo, A. A. ; Ackermann, M. ; Ajello, M. ; Cavazzuti, E. ; Giommi, P. ;
Nov - 2010
ISSN : 0004-637X ;
journal : The Astrophysical Journal

Issue : 2
type: Article Journal

Abstract
The extragalactic background light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above <10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the ³-ray flux of extragalactic sources such as blazars and gamma-ray bursts (GRBs). The Large Area Telescope on board Fermi detects a sample of ³-ray blazars with redshift up to z < 3, and GRBs with redshift up to z < 4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effect of ³-ray flux attenuation by the EBL. We place upper limits on the ³-ray opacity of the universe at various energies and redshifts and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the baseline model of Stecker et al. can be ruled out with high confidence.

keywords :