01-10-2012   13:30 hs.


Dr. M. Clementina Medina – IAR

Gamma ray telescopes are built to image γ-ray induced particle showers in the atmosphere. Telescopes are set in arrays in order to obtain a stereoscopic view of the atmospheric event, which allow efficient off-­?line background subtraction and a better determination of the γ-ray arrival direction. Moreover, to gain significantly in sensitivity, the next generation of Cherenkov telescopes shall make use of a very large reflective surface. For instance, CTA is an international project for the construction of the first observatory of very high energy γ-rays. Two sites, one in the North and one in the South are planned. In each of these sites an array of telescopes of different sizes will be installed. The final configuration of these arrays are not yet completely defined but the southern site of CTA will be composed of at least 50 telescopes of 3 different sizes and a total of ~5,000 m2 of mirrors will be necessary. The northern site, which is intended to be smaller, will require of order 3,500 m2 of mirrors. Such a massive production of mirrors has never been conducted for Cherenkov telescopes so far. For instance, the H.E.S.S. array after the completion of the large fifth telescope has a total reflecting surface of order 1,000 m2. Other running observatories involve 500 m2 (MAGIC, 2 telescopes) and 560 m2 (VERITAS, 4 telescopes) of mirrors.

Because of its large size, the reflector of a single Cherenkov telescope is composed of many individual mirror facets. The mirrors for H.E.S.S. and VERITAS are segments of solid glass aluminized on one side. For CTA mirrors, the glass solution is not a good option due to the large surface to be covered which constrains the cost of the facets. For a single telescope, less and larger facets is the more economic option but the glass ones become rapidly too heavy. This is an issue for the mechanical conception of the telescope and the energy required to make it move. The solution then is to develop composite mirrors, as in the MAGIC experiment for example.

In this talk, the latest advances on the development of these composite mirrors, carried out by the Irfu – CEA (France) team for CTA will be presented. More than 30 prototype mirrors have been already built with this tecnique and are being used to test their mechanical and optical properties.


Publicado en Charlas de divulgación, 2012.

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