The Orion Gamma-ray emission and the Orion-Eridanus bubble

We review the implications of the gamma-ray emission detected by COMPTEL in Orion, assuming that it is due to energetic particle (EP) interactions within the Orion clouds. We show that a series of independent arguments converge toward a model in which the EPs originate from the Orion-Eridanus bubble, located in front of the molecular cloud complex. We investigate in detail the question of energetics, introducing new indicators such as the total energy and the total mass of the EPs, and show that the average density of the EP confining region is a crucial parameter for any model of the Orion emission. Finally, we compare two extreme situations, where the EPs fill either the whole Orion-Eridanus bubble or a limited volume around the site of a recent supernova explosion in the Orion OB1 association. We conclude that the COMPTEL emission could be explained self-consistently by a hybrid solution in which a new supernova explodes within the energetic superbubble, propitious to particule acceleration. Possible generalisation to other Galactic sites is also investigated.