Very-high-energy (E>100 GeV) gamma-ray observations of astrophysical objects are a crucial tool for the understanding of the most violent non-thermal acceleration processes taking place in the Universe. The gamma rays allow to attack fundamental questions across a broad range of topics, including supermassive black holes, the origin of cosmic rays, and searches for new
physics beyond the Standard Model. Multi-wavelength observations of the center of the Milky Way unveil a complex and active region with the acceleration of cosmic rays to TeV energies
and beyond in astrophysical objects such as the supermassive black hole Sagittarius A* lying at the center of the Galaxy, supernova remnants or star-forming regions. The Galactic Centre (GC) stands out as one of the most studied regions of the sky in nearly every wavelength, and has been the target of some of the deepest exposures with high-energy observatories. Beyond the diversity of astrophysical accelerators, the GC should be the brightest source of dark matter particle annihilations in gamma rays.
The GC region harbors a cosmic Pevatron, i.e., a cosmic-ray particle accelerator to PeV energies, diffuse emissions from GeV to TeV such as the Galactic Centre Excess (GCE) whose origin is still unknown, potential variable TeV sources as well as likely unresolved source population. The interaction of electrons accelerated in these objects produces very-high-energy gamma rays
via the inverse Compton process of electrons scattering off ambient radiation fields. These gamma rays can also be efficiently produced through decays of neutral pions from inelastic
collisions protons and nuclei with the ambient gas. Among possible unresolved source populations in the GC region are millisecond pulsars in the Galactic bulge or an intermediate-mass (~20-10^5 Msun) black holes following the dark matter distribution of the Galactic halo. About 10^3 sources would be needed to explain the GCE emission. Such source population would leave characteristic imprints in the background fluctuations for which surveys of the GC region in TeV gamma rays with the H.E.S.S. observatory and the forthcoming CTA are unique to scrutinize them.
The H.E.S.S. observatory composed of five atmospheric Cherenkov telescopes detects gamma rays from a few ten GeV up to several ten TeV. H.E.S.S. has carried out extensive observations
of the GC with recently an observational campaign of the inner several degrees around the GC. The dataset accumulated so far provides an unprecedented sensitivity to study the acceleration and propagation of TeV cosmic rays and search for dark matter signals in the most promising region of the sky. These observations are unique to shape the observation programs of the future observatory CTA, optimize their implementation, and prepare future analyses.
The PhD thesis project will be focused on the analysis and interpretation of the observations carried out in the GC region by the H.E.S.S. over about 20 years. The first part of the work will be devoted to the low-level analysis of the GC data, the study of the systematic uncertainties in this massive GC dataset and the development of dedicated background models. In the second part, the PhD student will combine all the GC observations in order to search for TeV diffuse emissions, unresolved population of sources, and dark matter signals using multi-template analysis techniques including background modelling approaches. The third part will be dedicated to the implementation of the new analysis framework to CTA forthcoming data to prepare future GC analyses using the most up-to-date signal and background templates. In addition, the PhD student will be involved in the data taking and data quality selection of H.E.S.S. observations.