Multi-messenger gamma-ray counterpart of the IceCube neutrino signal

Abstract: A signal of high-energy extraterrestrial neutrinos from unknown source(s) was recently discovered by the IceCube experiment. Neutrinos are always produced together with gamma-rays, but the gamma-ray flux from extragalactic sources is suppressed due to attenuation in the intergalactic medium. We report the discovery of a gamma-ray excess at high Galactic latitudes starting at energies 300 GeV in the data of the Fermi telescope. We show that the multi-TeV gamma-ray diffuse emission has spectral characteristics at both low and high Galactic latitudes compatible with those of the IceCube high neutrino signal in the same sky regions. This suggests that these gamma-rays are the counterpart of the IceCube neutrino signal, implying that a sizable part of the IceCube neutrino flux originates from the Milky Way. We argue that the diffuse neutrino and gamma-ray signal at high Galactic latitudes originates either from previously unknown nearby cosmic ray "PeVatron" source(s), an extended Galactic CR halo or from decays of heavy dark matter particles.