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Context. In recent years, an in-depth gamma-ray analysis of the Orion regionhas been carried out by the AGILE and Fermi-LAT (Large Area Telescope) teamswith the aim of estimating the H2-CO conversion factor, XCO. The comparison ofthe data from both satellites with models of diffuse gamma-ray Galacticemission unveiled an excess at (l,b)=[213.9, -19.5], in a region at a shortangular distance from the OB star k-Ori. Possible explanations of this excessare scattering of the so-called "dark gas", non-linearity in the H2-COrelation, or Cosmic-Ray (CR) energization at the k-Ori wind shock.  Aims. Concerning this last hypothesis, we want to verify whether cosmic-rayacceleration or re-acceleration could be triggered at the k-Ori forward shock,which we suppose to be interacting with a star-forming shell detected inseveral wavebands and probably triggered by high energy particles.  Methods. Starting from the AGILE spectrum of the detected gamma-ray excess,showed here for the first time, we developed a valid physical model forcosmic-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 shockduring its "snowplow" expansion phase, we find that the Orion gamma-ray excesscould be explained by re-acceleration of pre-existing cosmic rays in theinteraction between the forward shock of k-Ori and the CO-detected,star-forming shell swept-up by the star expansion. According to ourcalculations, a possible contribution from freshly accelerated particles issub-dominant with respect the re-acceleration contribution. However, a simpleadiabatic compression of the shell could also explain the detected gamma-rayemission. Futher GeV and TeV observations of this region are highly recommendedin order to correctly identify the real physical scenario.

The Orion Region: Evidence of enhanced cosmic-ray density in a stellar wind forward shock interaction with a high density shell