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Register a new userImaging Atmospheric Cerenkov Telescopes: Techniques and Results
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Authors
S. M. Bradbury
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The hunt for cosmic TeV particle accelerators is prospering through Imaging Atmospheric Cerenkov Telescopes. We face challenges such as low light levels and MHz trigger rates, and the need to distinguish between particle air showers stemming from primary gamma rays and those due to the hadronic cosmic ray background. Our test beam is provided by the Crab Nebula, a steady accelerator of particles to energies beyond 20 TeV. Highly variable gamma-ray emission, coincident with flares at longer wavelengths, is revealing the particle acceleration mechanisms at work in the relativistic jets of Active Galaxies. These 200 GeV to 20 TeV photons propagating over cosmological distances allow us to place a limit on the infra-red background linked to galaxy formation and, some speculate, to the decay of massive relic neutrinos. Gamma rays produced in neutralino annihilation or the evaporation of primordial black holes may also be detectable. These phenomena and a zoo of astrophysical objects will be the targets of the next generation multi-national telescope facilities.
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Three different analysis techniques for Atmospheric Imaging System are presented. The classical Hillas parameters based technique is shown to be robust and efficient, but more elaborate techniques can improve the sensitivity of the analysis. A comparison of the different analysis techniques shows that they use different information for gamma-hadron separation, and that it is possible to combine their qualities.
Atmospheric Cerenkov telescopes are used to detect electromagnetic showers from primary gamma rays of energy > 300 GeV and to discriminate these from cascades due to hadrons using the shape and orientation of the Cerenkov images. The geomagnetic field affects the development of showers and diffuses and distorts the images. When the component of the field normal to the shower axis is sufficiently large (> 0.4 G) the performance of gamma ray telescopes may be affected.
After the launch and successful beginning of operations of the FERMI satellite, the topics related to high-energy observations of gamma-ray bursts have obtained a considerable attention by the scientific community. Undoubtedly, the diagnostic power of high-energy observations in constraining the emission processes and the physical conditions of gamma-ray burst is relevant. We briefly discuss how gamma-ray burst observations with ground-based imaging array Cerenkov telescopes, in the GeV-TeV range, can compete and cooperate with FERMI observations, in the MeV-GeV range, to allow researchers to obtain a more detailed and complete picture of the prompt and afterglow phases of gamma-ray bursts.
Ground-based gamma-ray astronomy experienced a major boost with the advent of the present generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) in the past decade. Photons of energies >~ 0.1 TeV are a very useful tool in the study of several fundamental physics topics, which have become an important part of the research program of all major IACTs. A review of some recent results in the field is presented.
The annihilations of WIMPs produce high energy gamma-rays in the final state. These high energy gamma-rays may be detected by imaging atmospheric Cherenkov telescopes (IACTs). Amongst the plausible targets are the Galactic Center, the centre of galaxy clusters, dwarf Sphreroidal galaxies and substructures in Galactic haloes. I will review on the recent results from observations of ongoing IACTs.
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