摘要：Context.Diffuse galacticγ-ray emission is produced by the interaction of cosmic rays (CRs) with the interstellar environment. The study ofγ-ray emission is therefore a powerful tool that can be used to investigate the origin of CRs and the processes through which they are accelerated.Aims.Our aim is to gain deeper insights into the nature ofγ-ray emission in the region of Orion, which is one of the best studied sites of ongoing star formation, by analysing data from the AGILE satellite. Because of the large amount of interstellar medium (ISM) present in it, the diffuseγ-ray emission expected from the Orion region is relatively high. Its separation from the galactic plane also ensures a very small contribution from foreground or background emission, which makes it an ideal site for studying the processes of particle acceleration in star-forming environments.Methods.The AGILE data are modelled through a template that quantifies theγ-ray diffuse emission expected from atomic and molecular hydrogen. Other sources of emission, such as inverse Compton (IC) scattering in interstellar radiation fields (ISRF) and extragalactic background, can be modelled as an isotropic contribution.Results.Gamma-ray emission exceeding the amount expected by the diffuse emission model is detected with a high level of significance. The main excess is in the high-longitude part of Orion A, which confirms previous results from theFermiLarge Area Telescope. A thorough analysis of this feature suggests a connection between the observedγ-ray emission and the B0.5 Ia starκOrionis.Conclusions.We present the results of the investigation ofγ-ray diffuse galactic emission from the region of Orion. The comparison between modelled and observed emission points towards the existence of higher-than-expectedγ-ray flux from a 1° radius region centred inκOrionis, compatible with the site where stellar wind collides with the ISM. Scattering on dark gas and cosmic-ray acceleration at the shock between the two environments are both discussed as possible explanations, with the latter hypothesis being supported by the hardness of the energy spectrum of the emission. If confirmed, this would be the first direct detection ofγ-ray emission from the interaction between ISM and a single star’s stellar wind.
关键词：Key wordsenacceleration of particlesstars: winds, outflowscosmic raysgamma rays: ISMISM: individual objects: Orion A
