A window on stochastic processes and gamma-ray cosmology through spectral and temporal studies of AGN observed with H.E.S.S.

Abstract : Fifty years after the discovery that quasars are extragalactic sources, their bright cores (AGN) and the jets that some of them exhibit still have plenty of secrets to share, particularly through observations in the gamma-ray band. Above 100 GeV, Cherenkov telescopes such as H.E.S.S. have detected 50 AGN, mostly blazars, objects whose jets are pointed toward the observer. The detection of two faint ones, 1ES 1312-423 and SHBL J001355.9-185406, is described in this thesis. Their multiwavelength spectra are reproduced with a synchrotron self-Compton model. The γ rays emitted by blazars are partly absorbed by the extragalactic background light (EBL), the second most intense cosmological background, which carries the integrated history of star formation. The first detection of this absorption above 100 GeV is performed, enabling the measurement of the EBL peak-amplitude in the optical band at the 20% level. In addition to these spectral studies, the fast flux-variations of blazars are investigated using the outbursts of PKS 2155-304 seen by H.E.S.S.. The observation of a skewed flux distribution and of an R.M.S.-flux correlation are interpreted within a kinematic model, where the emission is a realization of a stochastic process.
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Submitted on : Tuesday, May 14, 2013 - 12:58:12 PM
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Jonathan Biteau. A window on stochastic processes and gamma-ray cosmology through spectral and temporal studies of AGN observed with H.E.S.S.. High Energy Astrophysical Phenomena [astro-ph.HE]. Ecole Polytechnique X, 2013. English. ⟨pastel-00822242⟩

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