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On the site of the Gamsberg
in Namibia, the first telescope of the European and African(1)
experiment HESS (High Energy Stereoscopic System)(2)
, in which numerous CNRS laboratories- IN2P3(3) and INSU(4)-
are taking part, is being inaugurated on September 2 and 3, 2002. With
its very high definition camera, and its fast electronics, HESS is already
a world front-runner in experiments for detecting, on the ground, very
high density gamma rays. Observing these signals procures key information
on some of the most violent phenomena in the Universe. In 2003, when its
array of four telescopes will be operational, HESS will become world leader
in this field.
The inauguration ceremony is
taking place in the presence of representatives from the governments of
Namibia and of South Africa, from the University of Namibia, and from
the French and German Embassies in Namibia. On October 15, 2001, CNRS
and the University of Namibia (UNAM) signed a memorandum in Windhoek (Namibia),
the object of which is to promote scientific and technological co-operation.
The new-generation detector HESS will observe the Southern Universe under
excellent conditions, which was not possible with Cat and Celeste, two
experiments in which French teams are already involved(5)
, because they are located in the Northern Hemisphere. By detecting very
high energy gamma rays by means of the light flashes that these rays produce
by interacting with the Earth’s atmosphere (by the Cherenkov effect),
HESS will provide precious information on some of the most violent phenomena
in the Universe (supernovae, active galaxy nuclei, etc.).
It is under construction on the site of the Gamsberg in Namibia, at an
altitude of 1,800 meters, and 150 kilometers from the capital Windhoek,
in a desert-like region reputed for its clear and transparent nights.
Ultimately, this new experimental system will consist of an array of Cherenkov
telescopes(6) , four in the first phase which will be
completed by the end of 2003. Each one will comprise a mirror (108 square
meters in area, and 15 meters in focal length) made up of 382 small mirrors
that are 60 cm in diameter. The structure that will support this mirror
has a total height of 28 meters. During 2001, the first three structures
were installed. One of them has already been equipped with its mirrors.
In a second phase, once the principle has been demonstrated, it will be
possible to go from experimentation to an international observatory, by
increasing the number of telescopes so as to improve the sensitivity and
the flexibility of the instrument.
A camera weighing 800 kg
The first camera, an assembly measuring two meters in length for a diameter
of one meter sixty and a total weight of eight hundred kilograms, was
assembled and then installed on the structure in June 2002, the date on
which the experiment started collecting data. This camera, which is the
core of the experiment, is the major contribution from the French groups,
who have taken charge of designing and producing the mechanics, the electronics,
and the acquisition system of the cameras of the experiment. The modularity
of the system offers definite advantages in terms of maintenance, given
how far away the site is. The two major assets of the cameras are fine
imaging and fast electronics.
The addition of the three other telescopes of the first phase will enable
Hess to increase its sensitivity of flux detection further. With a detection
threshold in the vicinity of 80 GeV, and energy resolution of 15%, this
experiment will then have very high potential for discovering new sources
in the Southern Hemisphere.
Photos on request:
http://www.mpi-hd.mpg.de/HESS/public/full_images/full_images.htm
(1) Mainly
Germany, France, and the United Kingdom in Europe; Namibia and South Africa
in Africa.
(2) For more information on the Hess experiment:
http://lpnp90.in2p3.fr/~hess/brochure/HESS.html
(3) Institut national de physique nucléaire
et de physique des particules or “French National Institute for Nuclear
and Particle Physics” (IN2P3): Laboratoire de physique nucléaire
et hautes énergies (LPNHE), Laboratoire Leprince-Ringuet (LLR)
and Laboratoire de physique corpusculaire et cosmologie (PCC).
(4) Institut national des sciences de l’Univers
or “French National Institute for Sciences of the Universe”
(INSU): Centre d’étude spatiale des rayonnements (CESR), Laboratoire
d’astrophysique de l’observatoire des sciences de l’Univers
de Grenoble (LAOG) and Observatoire de Paris.
(5) The cosmic gamma ray detector Celeste was commissioned
in 2000, alongside the detector Cat, operational on the same site of Thémis
in the Eastern Pyrenees since 1996.
For more information: http://www.in2p3.fr/page/communication/com_info/dossierspresse/Themis/Themis.htm
(6) A Cherenkov telescope is made up of a passive
portion (the atmosphere), in which the high-energy cosmic rays interact,
and of an active portion (the telescope), constituted by a mirror which
focuses the light signals on a camera assigned the task of recording the
phenomenon.
For more details, see : http://lpnp90.in2p3.fr/~hess/brochure/img5.html
Researcher
contacts:
for physics
Bernard Degrange
Tel : +33 1 69 33 31 05
e-mail : degrange@poly.in2p3.fr
for instrumentation
Monique Rivoal
Tel : +33 1 44 27 43 64
e-mail : rivoal@in2p3.fr
Press contact
:
Magali Sarazin
Tel : +33 1 44 96 46 06
e-mail : magali.sarazin@cnrs-dir.fr
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