Constraints on Galactic Neutrino Emission with Seven Years of IceCube Data

TL;DR

This paper uses seven years of IceCube data to set upper limits on the Galactic contribution to high-energy neutrino flux, constraining its significance relative to the total diffuse flux.

Contribution

It introduces two novel maximum likelihood methods and applies multiple templates to constrain Galactic neutrino emission using extensive IceCube data.

Findings

Galactic neutrino flux contribution is less than 14% of the total diffuse flux above 1 TeV.

Developed two methods for spatially-extended flux analysis from the Galactic plane.

Set upper limits on neutrino emission from known high-energy Galactic gamma-ray sources.

Abstract

The origins of high-energy astrophysical neutrinos remain a mystery despite extensive searches for their sources. We present constraints from seven years of IceCube Neutrino Observatory muon data on the neutrino flux coming from the Galactic plane. This flux is expected from cosmic-ray interactions with the interstellar medium or near localized sources. Two methods were developed to test for a spatially-extended flux from the entire plane, both maximum likelihood fits but with different signal and background modeling techniques. We consider three templates for Galactic neutrino emission based primarily on gamma-ray observations and models that cover a wide range of possibilities. Based on these templates and an unbroken $E^{-2.5}$ power-law energy spectrum, we set 90% confidence level upper limits constraining the possible Galactic contribution to the diffuse neutrino flux to be relatively small, less than 14% of the flux reported in Aartsen et al. (2015a) above 1 TeV. A stacking method is also used to test catalogs of known high energy Galactic gamma-ray sources.