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Home page > PhD fellowships > Previous Calls > Proposed PhD subjects 2013-2016 > Deciphering extragalactic gamma-ray sources

Deciphering extragalactic gamma-ray sources

by Yannis Karyotakis - 25 February 2013

Topics : Gamma-ray Astrophysics-Astroparticle-Cosmology Proponents : Giovanni Lamanna (LAPP) & Pasquale Serpico (LAPTh)
Address : LAPP & LAPTh - 9, chemin de Bellevue B.P. 110 - 74941 Annecy-le-Vieux Cedex
Phone : + 33 4 50 09 16 79
Contact email :;;

Summary :

Active Galactic Nuclei (in particular in the “head-on” configuration of blazars) are among the most efficient objects in converting gravitational energy into non-thermal forms whichoriginating either directly from the acceleration sites or as byproduct of cosmic ray energy losses on the path to Earth-can be detectable in the form of photons, ranging from the radio to the TeV gamma-ray band.
The mechanisms of production and propagation of this radiation are still partially obscure and may require introducing new physical mechanisms to be fully understood. Existing models often fail to describe the complex phenomenology shown by these objects, like for example their time variability.
The proposed work will be developed at the interface of observational and data analysis activity with current and future gamma-ray Cherenkov telescopes within the H.E.S.S. – High Energy Stereoscopic System - and CTA - Cherenkov Telescope Array - research team at LAPP and phenomenological interpretation and modeling in collaboration with theoretical research team at LAPTh.
The activity will consist for example in:
• evaluating the extent to which a population study useful for physical diagnostics can be performed with existing data (highlighting e.g. systematic differences between flaring and non-flaring emissions.)
• testing different models for gamma-ray emission of AGNs with a multi-messenger approach (combining for example HESS data with publicly available data from Fermi, X-ray observatories, radio, etc.)
• computing the secondary radiation and effects in the propagation of the radiation to the Earth, taking into account for example the impact of the magnetic fields in the intergalactic medium (in turn using the gamma rays as a probe of this poorly known topic of cosmological interest.)
• improving existing theoretical models accounting for some plasma astrophysics aspects of the processes involved.
The candidate will have the opportunity to conduct her/his research and studies in the context of international research working groups dedicated to AGNs.
At more advanced stage the candidate is expected to be also involved into an observational proposal for further observations with HESS-II, as well as in some perspective work for CTA.
[1] HESS:
[2] CTA: