Ground based gamma-ray telescopes are providing currently key observations to explore the non-thermal universe. The High Energy Stereoscopic System (H.E.S.S.) is a recently commissioned system of four air Cherenkov telescopes observing mainly the southern sky from Namibia at very high energies (VHE) of 100 GeV and above. The data taken during the first two years of operation have unveiled a rich and diverse population of gamma-ray emitters including Pulsar Wind nebulae, the environment of the super-massive black hole in the heart of the Galaxy, shell type supernova remnants, an X-ray binary, so far unidentified Galactic sources, and extragalactic objects mainly of the type of so-called TeV blazars. The extension of H.E.S.S. (Phase II) is already under construction and is scheduled to begin operation in 2007: A large (35 m diameter) Cherenkov telescope is added to the existing 12 m diameter telescopes. The new telescope will extend the energy range towards 20 GeV closing the so far unobserved gap in the energy range between 10 and 100 GeV.
D. Horns, D. Horns,
"Ground-based gamma-ray observations with H.E.S.S.: status and future", Proc. SPIE 6267, Ground-based and Airborne Telescopes, 62670H (21 June 2006); doi: 10.1117/12.674384; https://doi.org/10.1117/12.674384