Gamma telescope

Gamma telescopes are instruments for receiving and measuring the gamma radiation coming from space . This most energetic electromagnetic radiation goes to astronomical objects v. a. from nuclear physical processes, from extremely hot objects (e.g. supernovae ) and with strong material acceleration through black holes .

The gamma-ray astronomy is the youngest branch of research in astronomy and is about the tremendous energy processes within active galactic nuclei and gamma-ray bursts to be clarified.

Space observatories

The radiation with wavelengths below 0.01 nm cannot be observed from the ground because the atmosphere in this energy range (photons> 200 keV) is impermeable. That is why gamma telescopes are only used in research satellites or space observatories.

Gamma rays even penetrate telescopes for grazing incidence (see X-ray optics ) and can therefore hardly be bundled with traditional methods. A massive radiation detector is required to capture gamma photons at all. The Compton Gamma Ray Observatory (in operation from 1991 to 2000) had a mass of 17 tons. The localization of the gamma sources was insufficient to identify the generating objects.

That is why NASA has combined its new Swift gamma-ray observatory (launched in 2004) with an X-ray telescope , which can locate the longer-wave X-rays that usually arrive at the same time to within a few arc seconds . As soon as Swift detects an outbreak in the gamma-ray range, the other detectors search for the source in the X-ray and also in the optical spectral range.

Other space gamma observatories were or are COS-B , Integral , High Energy Transient Explorer , AGILE , Fermi Gamma-ray Space Telescope .

Measurements on the ground

On the earth's surface, cosmic gamma rays can be detected indirectly through the triggering of particle showers in the air. The incident particles interact with air atoms, creating a cascade of secondary particles. In these air showers , nitrogen atoms emit their excitation energy as fluorescent light and Cherenkov radiation . The direction can be determined by measuring the delay along the shower front or stereoscopically (using several neighboring telescopes), the energy distribution from the particle numbers.

Such ground-based telescopes for gamma radiation are primarily the MAGIC system on La Palma and the High Energy Stereoscopic System (HESS) in Namibia.

literature

• J. Bennett, M. Donahue, N. Schneider, M. Voith: Astronomie (Chapter 6.4) , Ed. Harald Lesch, 5th edition, Pearson-Studienverlag, Munich-Boston-Harlow-Sydney-Madrid 2010
• Stars and space : a new window to the cosmos: gamma astronomy with HESS . SuW-Dossier 1/2010 "Seven Views into the Cosmos", Heidelberg 2010