Galactic neutrinos in the TeV to PeV range

Abstract

We study the contribution of Galactic sources to the flux of astrophysical neutrinos recently observed by the IceCube Collaboration. We show that in the simplest model of homogeneous and isotropic cosmic ray diffusion in the Milky Way the Galactic diffuse neutrino emission consistent with $\ensuremath{\gamma}$-ray (Fermi-LAT) and cosmic ray data (KASCADE, KASCADE-Grande and CREAM) is expected to account for only 4%--8% of the IceCube flux above 60 TeV. Direct neutrino emission from cosmic-ray-gas ($pp$) interactions in the sources will require an unusually large average opacity above 0.01. On the other hand, we find that the IceCube events already probe Galactic neutrino scenarios via the distribution of event arrival directions. Based on the latter, we show that most Galactic scenarios can only have a limited contribution to the astrophysical signal: diffuse Galactic emission ($\ensuremath{\lesssim}50%$), quasidiffuse emission of neutrino sources ($\ensuremath{\lesssim}65%$), extended diffuse emission from the Fermi bubbles ($\ensuremath{\lesssim}25%$) or unidentified TeV $\ensuremath{\gamma}$-ray sources ($\ensuremath{\lesssim}25%$). The arguments discussed here leave, at present, dark matter decay unconstrained.