03.12.2014 - (idw) Julius-Maximilians-Universitt Wrzburg

The astrophysicists Thomas Bretz and Daniela Dorner have developed a novel camera technology which for the first time allows sources of cosmic gamma radiation to be observed without interruption even when the moon is shining brightly. The scientists are now receiving an award in recognition of their work. The Wrzburg astrophysics department is thrilled: On 27 November, the Deutsche Physikalische Gesellschaft (DPG) announced that the 7,500 euro Gustav Hertz Award would be shared by scientist Daniela Dorner (35) and her colleague Thomas Bretz (40), who spent several years researching at the University of Wrzburg. The awards will be presented in Berlin on March 2015.

The DPG commends the laureates' "original and seminal impetus" to astroparticle physics with their contributions to enhancing Cherenkov telescopes. Bretz and Dorner achieved the success during their work for FACT (First Geiger-Mode Avalanche Photodiode Cherenkov Telescope), a joint project of Germany and Switzerland, which also involves scientists from TU Dortmund, ETH Zurich and the University of Geneva.

The challenge

So far, Cherenkov telescopes for observing cosmic gamma radiation have been based on detecting single photons by means of so-called photomultiplier tubes. Requiring high voltage in the kilovolt range, these photosensors are difficult to operate with outdoor telescopes. Moreover, they overload in the presence of bright moonlight and have to be switched off, which regularly results in data gaps.

But non-stop observation is crucial particularly in case of variable astronomical sources. Especially active galactic nuclei exhibit extreme variations in brightness which are crucial in order to understand physical processes taking place in the vicinity of black holes. Making progress in this field called for highly sensitive photosensors that require little electricity and no high-voltage supply while featuring nanosecond time resolution.

Putting an unusual idea into practice

To overcome this challenge, the scientists used an idea of the late physicist Eckhart Lorenz of the Max Planck Institute for Physics in Munich, namely to develop a camera with silicon-based semiconducting photosensors for a Cherenkov telescope. This idea seemed unsuitable at first and many experts advised against it.

But Thomas Bretz and Daniela Dorner nevertheless dared take the FACT collaboration one step further: They designed a camera, which was built at ETH Zurich, and installed it in a telescope on the Canary Island of La Palma in the Roque de los Muchachos Observatory, 2,200 metres above sea level.

The laureates' feat

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Breakthrough in astroparticle physics