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A multivariate particle classification approach is proposed and applied to the analysis of the data from H.E.S.S. (High Energy Stereoscopic System). The combination of results from the three shower reconstruction methods: Hillas, model and 3D-model, leads to a substantial gain in the discrimination power between photons and hadrons. The construction and use of a combined effective estimator improves by several factors the signal-to-background ratio which is extremely important in case of studies of the faint and extended sources. The results of this approach are presented for a typical set of sources. The consequent gain in the sensitivity is shown through a comparison to the H.E.S.S. published results. 相似文献
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We present a high-performance event reconstruction algorithm: an Image Pixel-wise fit for Atmospheric Cherenkov Telescopes (ImPACT). The reconstruction algorithm is based around the likelihood fitting of camera pixel amplitudes to an expected image template. A maximum likelihood fit is performed to find the best-fit shower parameters. A related reconstruction algorithm has already been shown to provide significant improvements over traditional reconstruction for both the CAT and H.E.S.S. experiments. We demonstrate a significant improvement to the template generation step of the procedure, by the use of a full Monte Carlo air shower simulation in combination with a ray-tracing optics simulation to more accurately model the expected camera images. This reconstruction step is combined with an MVA-based background rejection.Examples are shown of the performance of the ImPACT analysis on both simulated and measured (from a strong VHE source) gamma-ray data from the H.E.S.S. array, demonstrating an improvement in sensitivity of more than a factor two in observation time over traditional image moments-fitting methods, with comparable performance to previous likelihood fitting analyses. ImPACT is a particularly promising approach for future large arrays such as the Cherenkov Telescope Array (CTA) due to its improved high-energy performance and suitability for arrays of mixed telescope types. 相似文献
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Peter Cogan 《Astrophysics and Space Science》2005,297(1-4):275-281
The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is the next-generation ground-based gamma-ray observatory
that is being built in southern Arizona by a collaboration of 10 institutions in Canada, Ireland, the UK and the USA. VERITAS
is designed to operate in the range from 50 GeV to 50 TeV with optimal sensitivity near 200 GeV; it will effectively overlap
with the next generation of space-based gamma-ray telescopes. The first phase of VERITAS, consisting of four telescopes of
12 m aperture, will be operational by the time of the GLAST launch in 2007. Eventually, the array will be expanded to include
the full array of seven telescopes on a filled hexagonal grid of side 80 m. A prototype VERITAS telescope with a reduced number
of mirrors and signal channels has been built. Its design and performance is described here. The prototype is scheduled to
be upgraded to a full 499 pixel camera with 350 mirrors during the autumn of 2004.
The VERITAS collaboration consists of universities and institutions from Ireland, UK, USA and Canada. See for a full listing. 相似文献
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We have developed a method to measure the mirror reflectivity of telescopes. While it is relatively easy to measure the local reflectivity of the mirror material, it is not so straightforward to measure the amount of light that it focuses in a spot of a given diameter. Our method is based on the use of a CCD camera that is fixed on the mirror dish structure and observes simultaneously part of the telescope’s focal plane and the sky region around its optical axis. A white diffuse reflecting disk of known reflectivity is fixed in the telescopes focal plane. During a typical reflectivity measurement the telescope is directed to a selected star. The CCD camera can see two images of the selected star, one directly and another one as a spot focused by the mirror on the white disk. The ratio of the reflected starlight integrated by the CCD from the white disk to the directly measured one provides a precise result of the product of (mirror area × mirror reflectivity). 相似文献
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