CARDILLO , MARTINAMARTINACARDILLOMARCHILI, NicolaNicolaMARCHILIPIANO, GiovanniGiovanniPIANOGIULIANI, ANDREAANDREAGIULIANITAVANI, MARCOMARCOTAVANIMOLINARI, SergioSergioMOLINARI2021-02-172021-02-1720190004-6361http://hdl.handle.net/20.500.12386/30435Context. In recent years, an in-depth γ-ray analysis of the Orion region has been carried out by the AGILE and Fermi/LAT (Large Area Telescope) teams with the aim of estimating the H2-CO conversion factor, XCO. The comparison of the data from both satellites with models of diffuse γ-ray Galactic emission unveiled an excess at (l, b) = [213.9, -19.5], in a region at a short angular distance from the OB star κ-Ori. Possible explanations of this excess are scattering of the so-called "dark gas", non-linearity in the H2-CO relation, or cosmic-ray (CR) energization at the κ-Ori wind shock. Aims: Concerning this last hypothesis, we want to verify whether cosmic-ray acceleration or re-acceleration could be triggered at the κ-Ori forward shock, which we suppose to be interacting with a star-forming shell detected in several wavebands and probably triggered by high energy particles. Methods: Starting from the AGILE spectrum of the detected γ-ray excess, showed here for the first time, we developed a valid physical model for cosmic-ray energization, taking into account re-acceleration, acceleration, energy losses, and secondary electron contribution. Results: Despite the characteristic low velocity of an OB star forward shock during its "snowplow" expansion phase, we find that the Orion γ-ray excess could be explained by re-acceleration of pre-existing cosmic rays in the interaction between the forward shock of κ-Ori and the CO-detected, star-forming shell swept-up by the star expansion. According to our calculations, a possible contribution from freshly accelerated particles is sub-dominant with respect the re-acceleration contribution. However, a simple adiabatic compression of the shell could also explain the detected γ-ray emission. Futher GeV and TeV observations of this region are highly recommended in order to correctly identify the real physical scenario.STAMPAenArticle10.1051/0004-6361/2018336512-s2.0-85060872136000456967000002http://arxiv.org/abs/1901.01764https://www.aanda.org/articles/aa/full_html/2019/02/aa33651-18/aa33651-18.html2019A&A...622A..57CFIS/05 - ASTRONOMIA E ASTROFISICA