摘要：Context. In recent years, an in-depthγ-ray analysis of the Orion region has been carried out by the AGILE andFermi/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 diffuseγ-ray Galactic emission unveiled an excess at (l, b)=[213.9, −19.5], in a region at a short angular distance from the OB starκ-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 theκ-Ori wind shock.Aims. Concerning this last hypothesis, we want to verify whether cosmic-ray acceleration or re-acceleration could be triggered at theκ-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 detectedγ-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 Orionγ-ray excess could be explained by re-acceleration of pre-existing cosmic rays in the interaction between the forward shock ofκ-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 detectedγ-ray emission. Futher GeV and TeV observations of this region are highly recommended in order to correctly identify the real physical scenario.
关键词：enacceleration of particlesradiation mechanisms: non-thermalmethods: data analysisstars: windsoutflowscosmic raysgamma rays: ISM
