A low density of the Extragalactic Background Light revealed by the H.E.S.S. spectra of the BLLac objects 1ES 1101-232 and H 2356-309

Abstract

The unexpectedly hard spectra measured by HESS for the BLLacs 1ES 1101-232 and H 2356-309 has allowed an upper limit on the Extragalactic Background Light (EBL) to be derived in the optical/near-infrared range, which is very close to the lower limit given by the resolved galaxy counts. This result seems to exclude a large contribution to the EBL from other sources (e.g. Population III stars) and indicates that the intergalactic space is more transparent to gamma-rays than previously thought. A brief discussion of EBL absorption effects on blazar spectra and further observational tests to check this conclusion are presented, including the selection of new candidates for observations with Cherenkov telescopes.

6 pages, 9 figures, 1 table. Proceedings of the conference "The Multi-Messenger Approach to High-Energy Gamma-ray Sources", Barcelona, July 4-7 2006