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Abstract

The High Energy Stereoscopic system, H.E.S.S. is an array of four imaging atmospheric Cherenkov telescopes, designed for the study of non-thermal phenomena in the universe at very high energies (VHE). The sensitivity of telescope systems such as H.E.S.S. can considerably be improved by a better discrimination of the vast number of hadronic cosmic-ray background events against the very rare gamma-ray signal events. In this work, an elaborated discrimination technique – the Boosted Decision Tree method – has been developed and its capabilities in terms of gamma/hadron separation and improved sensitivity are demonstrated. In the second part, the BDT method is applied to data obtained in observations of massive star forming environments, namely the colliding wind binary η Carinae, the massive stellar cluster Westerlund 1 and the Starburst galaxy NGC 253. An upper limit on the gamma-ray flux of the famous colliding wind binary system η Carinae is derived and, for the first time, an alternative model for the high-energy emission observed by the Fermi satellite is presented. The detection of very extended VHE gamma-ray emission from the vicinity of Westerlund 1 is reported and thorough spectral and morphological tests are presented. Large parts of the resolved emission can be explained in a hadronic scenario, however, a decisive conclusion can not be drawn. Finally, the BDT method allowed to detect the first Starburst galaxy, namely NGC253, in VHE gamma rays. Spectral and morphological results are presented and suggest that large parts of the CR energy content are convectively and diffusively transported into the intergalactic medium.