Diffuse γ-ray emission from the galactic centre with H.E.S.S

The High Energy Stereoscopic System (H.E.S.S.) experiment uses the Imaging Atmospheric Cherenkov Technique (IACT) to study very-high-energy (VHE) $\gamma$-ray astrophysics. Its southern location provides the best opportunity to observe the Galactic Centre region. The Galactic Centre hosts many violent astrophysical objects and molecular gases. The diffuse TeV $\gamma$-ray emission in the Central Molecular Zone (CMZ) reveals the existence of powerful cosmic-ray (CR) accelerator(s) in the Galactic Centre. In particular, various studies postulated a PeV accelerator (PeVatron) continuously injecting CR protons to the ambience, resulting in a complex $\gamma$-ray morphology and absence of cutoff signature in the diffuse $\gamma$-ray spectrum. This study, using 11 years of H.E.S.S. data and an advanced 3D maximum-likelihood analysis method, re-establishes and constrains the diffuse $\gamma$-ray emission nature at 0.4 - 100 TeV. CR propagation is modelled and diffuse emission templates for the analysis are built accordingly, by assuming a hadronic origin in the Galactic Centre. This study unveils a CR energy cutoff at couple hundreds of TeV, opposing the postulation of a PeVatron existing in the Galactic Centre. Apart from the scenario of a continuously CR injecting source, an impulsively injecting source cannot be ruled out.