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The 2009 Fermi Symposium

H.E.S.S. VHE Gamma-ray Sources Associated with Molecular Clouds

Karl P. Kosack


We report on the observation of several Galactic sources of VHE gamma rays discovered by the H.E.S.S. system of Cherenkov telescopes that can be associated with the interaction of high-energy particle accelerators and molecular clouds. One of the major goals of gamma-ray astronomy has been to discover the sources of the highest-energy cosmic rays, which are long thought to be accelerated in supernova remnants. Though H.E.S.S. has successfully detected the resolved shells of young supernova remnants, it remains difficult to separate whether the emission seen is produced by leptons or hadrons. Fortunately, even in the case where the SNR shock itself produces little or no detectable VHE emission, gamma rays can be generated where the shock is directly interacting with a dense molecular cloud, and also when high-energy protons escape the remnant (or other acceleration site) and diffuse into a nearby cloud. In these cases, a hadronic scenario is favored where the clouds act as target material for high-energy protons and produce gamma rays through pion decay. Therefore, the gamma-ray sources discussed here provide a unique insight into the physics of supernova remnants and the origin of galactic cosmic rays, particularly when combined with multi-wavelength data from Fermi and lower-energy telescopes.