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GRASP - Development of an event reconstruction method using a Gamma Ray Air Shower Parameterisation and application to gamma-ray sources with H.E.S.S.

Hillert, Andreas

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The H.E.S.S. experiment, with its high sensitivity and large field-of-view, is an ideal instrument to survey the Milky Way in VHE gamma-rays. An accurate reconstruction of the gamma-ray direction as well as a strong reduction of the hadronic background is essential for the analysis of the data. In this work a reconstruction algorithm is developed that applies a fit of pixel amplitudes to an expected image obtained from a Gamma Ray Air Shower Parameterisation (GRASP). This parameterisation was obtained using Monte Carlo air shower simulations by parameterising the angular Cherenkov photon distribution with suitable analytical functions. Furthermore, it provides new classifying variables to differentiate gamma-ray induced air showers from hadronic ones. The reconstruction of air shower parameters is achieved by a maximum likelihood fit and improves the angular resolution by 20-30% with respect to traditional image moment analysis methods. In combination with a MVA-based background rejection method using these new classifying variables the sensitivity can be improved by about 70%. An analysis of the Pulsar Wind Nebula MSH 15-5-2 and investigation of its morphology and spectral properties show an indication of energy dependent morphology in VHE gamma-rays.

Document type: Dissertation
Supervisor: Hofmann, Prof. Dr. Werner
Date of thesis defense: 24 July 2014
Date Deposited: 04 Aug 2014 09:42
Date: 2014
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
DDC-classification: 520 Astronomy and allied sciences
530 Physics
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