Hadronic nature of high-energy emission from the Galactic Ridge

TL;DR

This paper confirms that high-energy gamma-ray and neutrino emissions from the Galactic Ridge are produced by interactions of high-energy protons, demonstrating variability in cosmic ray spectra across the Milky Way using multi-messenger observations.

Contribution

It provides the first unambiguous multi-messenger evidence linking neutrino and gamma-ray emissions to proton interactions in the Galactic Ridge, revealing cosmic ray spectrum variability.

Findings

Neutrino flux from the Galactic Ridge confirmed by IceCube and ANTARES.

Gamma-ray and neutrino spectra consistent with pion decay from proton interactions.

Cosmic ray spectrum in the Galactic Ridge is harder than local spectrum.

Abstract

We show that the IceCube observation of the Galactic neutrino flux component confirms the hint of detection of neutrinos from the Galactic Ridge (the inner part of the Milky Way disk within the Galactic longitude |l|<30 degrees), previously reported by the ANTARES collaboration. This confirmation indicates that the bulk of the high-energy flux from the Galactic Ridge in multi-TeV band is produced by interactions of high-energy protons and atomic nuclei, rather than electrons. We show that both ANTARES and IceCube measurements agree with the Fermi-LAT telescope measurements of the gamma-ray emission from the Ridge. The multi-messenger (neutrino plus gamma-ray) spectrum of the Ridge over a broad energy range from 10 GeV to 10 TeV is consistent with a model of pion decay emission produced by a power-law distribution of protons with a slope Gamma~2.5, harder than that of the locally observed cosmic ray spectrum. This provides for the first time an unambiguous multi-messenger demonstration of the variability of the spectrum of cosmic rays across the Galactic disk.