High Energy Stereoscopic System

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High Energy Stereoscopic System (H.E.S.S.)
HESS II gamma ray experiment official logo.jpg
Logo of the H.E.S.S. experiment
Organization H.E.S.S. Collaboration
Location Khomas Highland, Namibia
Coordinates 23°16.28′S 16°30′E / 23.27133°S 16.500°E / -23.27133; 16.500Coordinates: 23°16.28′S 16°30′E / 23.27133°S 16.500°E / -23.27133; 16.500
Altitude 1,800 m (5,900 ft)
Collecting area H.E.S.S. I: 108 m2
H.E.S.S. II: 614 m2
Focal length H.E.S.S. I: f/0.8 (15 m)
H.E.S.S. II: 36 m
Website http://www.mpi-hd.mpg.de/hfm/HESS/

High Energy Stereoscopic System (H.E.S.S.) is a system of Imaging Atmospheric Cherenkov Telescopes (IACT) for the investigation of cosmic gamma rays in the energy range of 30 GeV to 100 TeV. The acronym was chosen in honour of Victor Hess, who was the first to observe cosmic rays.

The name also emphasizes two main features of the installation, namely the simultaneous observation of air showers with several telescopes, under different viewing angles, and the combination of telescopes to a large system to increase the effective detection area for gamma rays. H.E.S.S. permits the exploration of gamma-ray sources with intensities at a level of a few thousandth parts of the flux of the Crab Nebula.

H.E.S.S. has five telescopes, four with a mirror just under 12m in diameter, arranged 120m apart from each other in a square, and one larger telescope with a 28m mirror, constructed in the centre of the array. This current system, called H.E.S.S. II, saw its first light at 0:43 a.m. on 26 July 2012.[1]

As with other gamma-ray telescopes, H.E.S.S. observes high energy processes in the universe. Gamma-ray producing sources include supernova remnants, active galactic nucleii and pulsar wind nebulae. It also actively tests unproven theories in physics such as looking for the predicted gamma-ray annihilation signal from WIMP dark matter particles and testing lorentz invariance predictions of loop quantum gravity.

H.E.S.S. is located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg, an area well known for its excellent optical quality. The first of the four telescopes of Phase I of the H.E.S.S. project went into operation in Summer 2002; all four were operational in December 2003.

In 2004 H.E.S.S. was the first IACT experiment to spatially resolve a source of cosmic gamma rays.

In 2005, it was announced that H.E.S.S. had detected eight new high-energy gamma ray sources, doubling the known number of such sources. As of 2014, more than 90 TeV gamma-ray sources were discovered by H.E.S.S.[2]

The five-telescope H.E.S.S. array 
A 1/30 scale model of a HESS telescope on display in the Science Museum, London
Four telescopes in operation at night 

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