Massive protostars as gamma-ray sources

Abstract

<i>Context. <i/>Massive protostars have associated bipolar outflows with velocities of hundreds of km s<sup>-1<sup/>. Such outflows can produce strong shocks when they interact with the ambient medium leading to regions of nonthermal radio emission.<i>Aims. <i/>We aim at exploring under which conditions relativistic particles are accelerated at the terminal shocks of the protostellar jets and whether they can produce significant gamma-ray emission.<i>Methods. <i/>We estimate the conditions necessary for particle acceleration up to very high energies and gamma-ray production in the nonthermal hot spots of jets associated with massive protostars embedded in dense molecular clouds.<i>Results. <i/>We show that relativistic bremsstrahlung and proton-proton collisions can make molecular clouds with massive young stellar objects detectable by the <i>Fermi<i/> satellite at MeV-GeV energies and by Cherenkov telescope arrays in the GeV-TeV range.<i>Conclusions. <i/>Gamma-ray astronomy can be used to probe the physical conditions in star-forming regions and particle acceleration processes in the complex environment of massive molecular clouds.