15 Décembre – Thesis defense - Arnaud Mares
10 h Room seminar - CENBG (Gradignan)
Search for proton accelerators in the Galaxy with the Fermi-LAT and the H.E.S.S. telescopes.
The emergence of gamma-ray astronomy has deepened our understanding of the origin of cosmic rays and the mechanisms responsible for their acceleration. Despite observational evidences that supernova remnants and pulsar wind nebulae are efficient electrons accelerators, evidences for the acceleration of protons, which represent 90% of the cosmic rays, are much more scarce.
This thesis presents the analysis of HESS J1640-465 and the PeVatron candidate HESS J1641-463 using GeV data from the Fermi satellite to constrain the emission processes and the nature of these sources. This analysis revealed that their multi-wavelength emissions are very well modelled by systems composed of a pulsar and its nebula, in which high-energy electrons scatter on the ambient photon fields by inverse Compton scattering. On the other hand, the complementary analysis of data of the H.E.S.S. Cherenkov telescope array provides arguments in favour of a self-consistent scenario in which the TeV emission from both sources is produced by the interaction of high energy protons with molecular clouds. This scenario explains by itself the very hard gamma-ray spectrum of HESS J1641-463 at TeV, as well as that of a new source in coincidence with a molecular cloud linking these sources: PNM 4041.
In the context of the study of the PeVatron candidate HESS J1641-463, an improvement of Model++ analysis chain of H.E.S.S was also developed. The recovery of cut images of electromagnetic showers, not considered until now, improves the effective area of all Model++ analysis profiles while keeping an angular resolution lower than 0.1° up to 50 TeV. By slightly modifying the values of the parameters used in Model++, the recovery of these events improves the significance, the number of gamma-ray photons and the signal-to-noise ratio whatever the zenith angle of the observed sources. A dedicated high-energy optimisation has been performed in order to maximize the significance of sources above 5 TeV for the search and study of Galactic PeVatrons. This optimisation improves the effective area by more than 85% at 80 TeV at low zenith angles compared to the H.E.S.S. Faint profile, while maintaining a very good angular and energy resolution.