The origins of the extraterrestrial neutrinos observed in IceCube have yet to be determined. In this study we perform a one-point fluctuation analysis of the six-year high-energy starting event shower data, with fixed non-Poissonian contributions from atmospheric, galactic and some extragalactic components, as well as an isotropic (and weakly non-Poissonian) template. In addition to the star-forming galaxies and blazars, our analysis suggests the presence of an additional isotropic component, not associated with any detected class of point sources, with best-fit intensity of $(2.8\pm 0.2)\times {10}^{-18}(E/100\mathrm{TeV}{)}^{-2.7\pm 0.5}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}{\mathrm{GeV}}^{-1}$. For the first time, we also consider high-energy extrapolations of several phenomenological models for the diffuse galactic emission (tuned to both local cosmic-ray data and diffuse gamma-ray emission in the GeV–TeV domain). We demonstrate the potential of our framework in discriminating between different scenarios, with possible implications on the physics of cosmic-ray transport in the TeV–PeV range.

• Received 13 November 2017

DOI:https://doi.org/10.1103/PhysRevD.97.103017