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TeV observations of hard spectrum active galactic nuclei with HESS-I and HESS-II

Cologna, Gabriele

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Abstract

In my PhD thesis, I present the results of the analysis of three point-like gamma-ray emitters observed at very high energies with the High Energy Stereoscopic System (H.E.S.S.): the two well known blazars 1ES 0229+200 and Mrk 501, and HESS J1745-290. The nature of the latter source is unclear, although it is likely linked to Sgr A∗, the black hole at the center of the Galaxy. I make use of multiwavelength observations in order to assess the physical properties of the three sources and of the ambient medium, both via spectral and variability studies and by comparison with models and predictions found in the literature. I also present systematic comparisons of the gamma-ray energies as reconstructed for different sub-arrays of the H.E.S.S. system.

I search for correlated variability in simultaneous x-ray and very high energy observations of Sgr A∗ in order to understand whether or not the gamma-ray emission of HESS J1745-290 originates from the black hole, making it an active galactic nucleus. The correlation of the flux variability in different energy bands for 1ES 0229+200 supports the interpretation of a synchrotron self Compton emission model for this source. The refined spectrum of the inverse Compton peak helps constraining the strength of the intergalactic magnetic field. The hard intrinsic spectrum of Mrk 501 shows a dependency on the flux state. The spectrum can be used to constrain the extragalactic background light intensity in the mid-infrared for the redshift of the source. Multiwavelength observations suggest the presence of at least two emission zones or mechanisms in order to explain the broadband emission.

Item Type: Dissertation
Supervisor: Wagner, Prof. Dr. Stefan J.
Date of thesis defense: 11 May 2016
Date Deposited: 01 Jun 2016 08:08
Date: 2016
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Subjects: 520 Astronomy and allied sciences
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