What IceCube data tell us about neutrino emission from star-forming galaxies (so far)

Very recently, the IceCube Collaboration reported a flux of neutrinos in the energy range 50 TeV < E_ν< 2 PeV, which departs from expectations from atmospheric background at the 5.7σlevel. This flux is in remarkable agreement with the expected diffuse flux of neutrinos from starburst galaxies, and the 3 highest energy events have uncertainty contours encompassing some of such systems. These events, all of which have well-measured energies above 1 PeV, exhibit shower topologies, for which the angular resolution is about 15^\circ. Due to this angular uncertainty and the a posteriori nature of cuts used in our study it is not possible to assign a robust statistical significance to this association. Using muon tracks, which have angular resolution < 1^\circ, we compute the number of observations required to make a statistically significant statement, and show that in a few years of operation the upgraded IceCube detector should be able to confirm or refute this hypothesis. We also note that double bang topology rates constitute a possible discriminator among various astrophysical sources.

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