Laboratory link : http://irfu.cea.fr/dphp/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3429
More : https://www.mpi-hd.mpg.de/hfm/HESS/
Very high energy gamma ray astronomy observes the sky above a few tens of GeV. This emerging field of astronomy has been in constant expansion since the early 1990s, in particular since the commissioning of the H.E.S.S. array in 2004 in Namibia. IRFU/CEA-Paris Saclay is a particularly active member of this collaboration from the start. It is also involved in the preparation of the future CTA observatory (Cherenkov Telescope Array), which should come into operations by 2024. The detection of gamma rays above a few tens of GeV makes it possible to study the processes of charged particles acceleration within objects as diverse as supernova remnants or active galactic nuclei. Through this, H.E.S.S. aims in particular at answering the century-old question of the origin of cosmic rays.
HESS allows measuring the direction, the energy and the arrival time of each detected photon. The time measurement makes it possible to highlight sources which present significant temporal or periodic flux variations. The study of these variable emissions (transient or periodic), either towards the Galactic Center or active nuclei of galaxies (AGN) at cosmological distance allows for a better understanding of the emission processes at work in these sources. It also helps characterizing the medium in which the photons propagate and testing the validity of some fundamental physical laws such as Lorentz invariance. It is possible to probe a wide range of time scales variations in the flux of astrophysical sources. These time scales range from a few seconds (gamma ray bursts, primordial black holes) to a few years (binary systems of high mass, active galaxy nuclei).
One of the major successes of the first decade of data collection of H.E.S.S. was to conduct the first Galactic Plan survey of sources in this energy range. This survey, comprising more than 10 years of data, combines observations dedicated to known sources, such as the Galactic Center or some supernova remnants, as well as blind observations for the discovery of new sources. The subject of the thesis proposed here deals with one aspect of the study of the Galactic plane that remains to be explored: research and study of the variability and periodicity of gamma-ray sources throughout this dataset.