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T: Fachverband Teilchenphysik

T 402: γ-Astronomie III

T 402.5: Talk

Thursday, March 8, 2007, 17:45–18:00, INF 308 Kl. HS

Probing the diffuse extragalactic background light with gamma-rays from blazars — •Luigi Costamante for the H.E.S.S. collaboration — Max-Planck-Institut fuer Kernphysik, Heidelberg

The diffuse Extragalactic Background Light (EBL) carries important information on the formation and evolution of the luminous structures in the Universe, but its knowledge is still uncertain. Gamma-rays from extragalactic sources can probe this diffuse field owing to the photon-photon collision and pair production process. The recent HESS results on the blazars 1ES 1101-232 and H 2356-309 represented a breakthrough on this issue. Their unexpectedly hard spectra allow an upper limit to the EBL to be derived in the Opt-NIR band, which is very close to the lower limit given by resolved galaxy counts. This result seems to exclude a large contribution to the EBL from other sources (e.g. Pop III stars) and indicates that intergalactic space is more transparent to gamma-rays than previously thought.