Paris, 14 June 2010
Supernovas, black holes, active galactic nuclei, etc.: the existence of the most violent phenomena in the Universe is revealed by cosmic gamma rays(4), the sources of which are systematically tracked down. This is the objective of the HESS(5) experiment. Composed of four telescopes of 12 meters in diameter, the HESS observatory is situated on a high plateau in Namibia, in South-West Africa(6). Since it was commissioned in 2004, HESS has opened a new window on the Universe by unveiling a multitude of previously undetected gamma ray sources: of the 84 sources discovered to date, 53 have been detected by HESS. It is currently one of the best-performing ground-based gamma observatories in the world. Unlike conventional telescopes that observe the stars directly, the HESS telescopes lie in wait for the furtive light produced by the interaction in the atmosphere of high-energy gamma rays coming from the Universe. In fact, such gamma rays generate veritable showers of particles similar to those produced in particle accelerators. To capture the signal from these interactions in the atmosphere, the four HESS telescopes are equipped with extremely sensitive and rapid electronic cameras, enabling HESS to map celestial objects emitting high-energy gamma radiation.
In order to increase the instrument's sensitivity and reveal some of the mysteries of our Universe, the researchers involved in HESS are developing an even more efficient device, known as HESS-II, which consists in adding a very large central telescope of 28 m in diameter to the existing system. The 596 m2 of this telescope's mirror (compared to 107 m2 for each of the 4 telescopes already in place) will concentrate the light on a camera that has just been built. With a sensitive surface area of 2.15 m in diameter and a granularity(7) twice that of the cameras used at present, it will be able to detect gamma photons one by one with a response time on the nanosecond (10-9 s) scale. This camera is a real eagle's eye and the key component of the fifth telescope. It represents France's main contribution, with IN2P3/CNRS as project manager. The French laboratories, backed up by a network of industrial partners, built on the expertise acquired in developing cameras for the first four telescopes. The new camera still needs to undergo calibration tests before being shipped to Namibia and installed on the fifth telescope, which is expected to be fully operational by 2011.
HESS-II, which is more sensitive and covers a broader energy range, will pave the way for new discoveries and will make it possible to expand the catalogue of high-energy sources in the Universe. More specifically, this new network should help to increase the number of known sources emitting high-energy gamma rays and significantly improve images of celestial objects, such as the remains of supernovae.
International HESS collaboration
The HESS collaboration is a leader both in Europe and worldwide. It presently encompasses 180 researchers from 28 laboratories in 12 different countries, mainly Germany and France. The collaboration has achieved a plethora of scientific results, widely recognized internationally. These achievements have also been possible thanks to the human and computing resources at the Centre de Calcul of IN2P3. The HESS collaboration was rewarded with the Descartes Research Prize in 2006 and the Bruno Rossi Prize in 2010. These prizes were respectively awarded by the European Commission and by the American Astronomical Society.
French laboratories involved in HESS
- Laboratoire Astroparticule et Cosmologie (CNRS/Université Paris Diderot-Paris 7/CEA/Observatoire de Paris),
- Laboratoire d'Annecy-le-Vieux de Physique des Particules (CNRS/Université de Savoie),
- Laboratoire Leprince-Ringuet (CNRS/École Polytechnique),
- Laboratoire de Physique Nucléaire et de Hautes Energies (CNRS/UPMC/Université Paris Diderot-Paris 7),
- Laboratoire de Physique Théorique et Astroparticules (CNRS/Université de Montpellier 2),
- Centre d'Etude Spatiale des Rayonnements (CNRS/Université Toulouse 3, Observatoire Midi-Pyrénées/INSU),
- Laboratoire d'Astrophysique de Grenoble (CNRS/Université Joseph Fourier, Observatoire des Sciences de l'Univers de Grenoble/INSU),
- Laboratoire « Univers et Théories » (Observatoire de Paris/CNRS/Université Paris Diderot-Paris 7),
- Institut de Recherche sur les Lois Fondamentales de l'Univers (CEA-Irfu)
© Collection Ecole Polytechnique, Philippe Lavialle
Upper part of the camera: the granularity of its 2.15 m diameter photosensitive area is twice that of the cameras currently used in HESS.
(1) Institut National de Physique Nucléaire et de Physique des Particules of CNRS
(2) Institut National des Sciences de l'Univers of CNRS
(3) Institut de Recherche sur les Lois Fondamentales de l'Univers of CEA
(4) Composed of photons, like visible light or X-rays, gamma radiation has much higher energy, reaching one thousand billion times the energy of visible light.
(5) High Energy Stereoscopic System.
(6) HESS is located in a very sunny region at an altitude of 1,800 m, two factors that are very favorable to gamma ray detection.
(7) The image elements (pixels) are twice as numerous and twice as sharp in HESS-II as in the present system.
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