12-20 July 2017
Asia/Seoul timezone
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[DM035] Molecular clouds as the origin of the Fermi gamma-ray GeV-excess


  • Iris GEBAUER

Primary authors



We study the ”GeV-excess” of diffuse gamma-rays in the Galactic halo with a template fit based on energy spectra for each possible process of gamma-ray emission. In addition to the ”standard” physical processes for gamma-ray production from π0 decays produced by diffused cosmic rays, inverse Compton scattering and Bremsstrahlung one finds clear evidence for two additional processes: π0 production in sources during acceleration and π0 production in molecular clouds. The first one is characterized by nuclear cosmic rays with a hard 1/E^2 spectrum, expected from diffusive shockwave acceleration and can be traced by the 1.8 MeV gamma-ray line from radioactive 26 Al decays, which is synthesized in sources. The second one is characterized by nuclear cosmic rays inside molecular clouds with a sharp cutoff below 14 GV, which is most clearly observed in the dense Central Molecular Zone encircling the Galactic center in the Galactic disk. Molecular clouds can be traced by the rotation lines of the CO molecule. The cutoff leads to a suppression of low energy nuclei, which causes a shift in the maximum of the gamma-ray spectrum to higher energies, the hall-mark of the ”GeV-excess”, which has been previously interpreted as a dark matter annihilation signal.