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Document Version Version Comment Date Status
395645.0 [No comment] 07.01.2009 10:18 Released

ID: 395645.0, MPI für Kernphysik / High-Energy Astrophysics
A Study of Very High Energy Gamma-Ray Emission from Extragalactic Objects with H.E.S.S.
Authors:Nedbal, Dalibor
Referees:Hofmann, Werner; Wagner, Stefan
Date of Approval (YYYY-MM-DD):2008-12-17
Name of University:Ruprecht-Karls Universität
Place of University:Heidelberg
Physical Description
(e.g. Total Number of Pages):
VIII, 146 S. : Ill., graph. Darst.
Audience:Experts Only
Abstract / Description:Very-high-energy (VHE) γ-ray astronomy has opened a unique window into the Universe of the highest energies, allowing one to efficiently investigate the question of the origin of high-energy cosmic rays. The H.E.S.S. array of four imaging atmospheric Cerenkov (IACT) telescopes is utilised in this work to search for VHE γ-rays from selected candidate extragalactic objects that are expected to contain significant populations of cosmic rays: galaxy clusters Abell 496, Abell 85, Coma cluster, Abell 754, Centaurus cluster and Hydra A, starburst galaxies NGC 253 and M 83, from an ultraluminous infrared galaxy Arp 220 and from an active galactic nucleus (AGN), RGB J0152+017. The instrument is described, giving an overview of the IACT technique, the data acquisition, data-quality determination, calibration, performance, and the actual analysis that was used to obtain
the results.
In the starburst galaxy NGC 253, a hint of a VHE signal is found at a ∼3σ significance level. No significant VHE signal is found from the remaining non-AGN objects, and upper limits are presented. The upper limits of Abell 85 and Abell 496 are used to constrain the non-thermal to thermal energy ratio, which is ∼8% for Abell 85 and is thus challenging
theoretical estimates. The AGN, RGBJ0152+017, is in this work discovered in VHE γ rays and its first-time broad-band spectral energy distribution is presented. While no
new type of a VHE emitter is established, the presented theoretical expectations are very promising for the planned CTA observatory.
Document Type:PhD-Thesis
Affiliations:MPI für Kernphysik/Group of W. Hofmann/Experimental High-Energy Astrophysics (M. Panter, G. Hermann)
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