Speaker
Description
Imaging Atmospheric Cherenkov Telescopes measure cosmic gamma radiation at very-high-energies (VHE) between 20 GeV and about 100 TeV. While most of the observations are devoted to study astrophysical processes in the sources of the gamma-ray emission (Supernova remnants, pulsar wind nebulae, gamma-ray binaries, active galactic nuclei, gamma ray bursts etc), distant gamma rays can also be used to test cosmological models. In particular, the cosmic background low-energy photon field (called Extragalactic Background Light, EBL) is causing energy dependent absorption feature in the observed spectra of VHE gamma-ray sources. Alternatively, if the density of the EBL is known, the absorption feature can be used to determine the Hubble constant H0. Moreover, measured temporal and spatial emission recorded from distant blazars is sensitive to intergalactic magnetic fields in the voids. In this presentation I explain the technique used, the results obtained so far and give an outlook to the future prospects.
