Inauguration at the Paris Observatory of the « Gamma-ray Cherenkov Telescope »

Until the end of the 1980s, astrophysicists only knew the Universe via its radio, infra-red, visible, X and low energy gamma ray emissions, as well as via cosmic ray particles However, there are also in the Universe many sources of extreme gamma rays. A primary objective is to understand the mechanisms which produce particles which in turn then produce radiation 100 billion times more energetic than visible light, and hence to probe deeper some of the key problems of contemporary astrophysics, such as, for example, the physics of compact objects and black holes.

CTA : a world observatory

An entirely new international observatory, the « Cherenkov Telescope Array » (CTA) was born from the need to study these sources. This world class initiative aims to build the largest and most sensitive high energy gammma ray telescope : it will be composed of a network of about 100 telescopes, spread over two sites, in the southern and northern [1] hemispheres. It will be built suring the period 2016 à 2022, and will be partially operational towards 2018.

GCT – the first prototype of the CTA telescope, equiped with a superpowerful camera

Part of the smallest of the three sizes of the telescopes which make up the CTA network (Small size telescope -SST), the first prototype of the GCT is almost ready for first light. It will coverf the CTA extreme energy range from 5 to 300 TeV (tera-électronvolts). Roughtly 70 SSTs will be needed for the CTA to be sufficiently sensitive at these colossal enerrgies.

This is the first CTA prototype to be equiped with a working camera.
In order to be able to detect the weak light flashes produced by the cosmic rays as they strike the terrestrial atmosphere [2], the telescope camera has to be about one miilion time faster than a digital reflex camera (of the DSLR type [3]). This is done by digitizing at high speed, coupled to a switching technique which can register images at a rate of a billion per second, and sufficiently sensitiveas to resolve individual photons.

In addition to that at the Observatory, two other SSTs sites in the world are being prototyped and tested : in Italy and in Poland. At present, it is foreseen that over twenty GCTs will make up the CTA network.

A new type of optical system

The Meudon prototype is one of the first realizations of a compact telescope using the so-called Schwarzschild-Couderc two mirror system, which had never been used in optical astronomy but was recently recognized as a particularly promising system for ground based gamma ray astronomy. This system produces good images over a wide field of view, and enables one to use telescopes and cameras which are lighter than the one mirror systems generally used till now for gamma ray astronomy.

An international collaboration

The GCTs will be built within the framework of an international collaboration putting together contributions from institutes and universities spread over many countries, including Germany, Australia, France, Japan, Holland and the United Kingdom.
The GCT consortium is at present made up of the following members : Aix-Marseille
Universitéy(France), CNRS (France), the Max-Planck Institute fsor Nuclear Physics
(Heidelberg, Germany), the Paris Observatory (France), and the universities of
Durham, Leicester, Liverpool et Oxford (United Kingdom), Nagoya (Japan), Erlangen-
Nurenberg (Germany), Adelaïde (Australia) et Amsterdam (Holland).

To know more about the CTA

Over 1 000 scientists and engineers from 32 countries [4], representing over 170 research centres, are participating in the project. The CTA will be an obervatory accessible to a wide community of astrophysicists and physicists, and will lead to a better understanding of the high energy, turbulent and non-thermal universe. The CTA observatory will detect high energy cosmic rays with a heretofore unequalled precision and with a sensitivy ten times better than existing instruments, giving us a new view of the most extreme and violent phenomena in the Universe.

The inaugration at the Meudon site of the Paris Observatory

Addresse : 11 avenue Marcelin Berthelot, 92195 Meudon

• 14h30 > Welcome at the lecture theatre in the building no.18.
  • Opening speech by Claude Catala, President of the Paris Observatory
  • Speeches by the CNRS representatives of the « Science and Technology Facilities Council » (STFC, United Kingdom), of the CTA consortium and the GCT consortium.
• 16h > on the Paris Observatory campus : visit of the prototype telescope
• 17h30 > the Uranie Hall at the château (building 9) : Cocktail