article · Physics Letters B
Interactions of cosmic rays with the interstellar medium in the inner Milky Way produce gamma rays and an associated neutrino flux from the Galactic Ridge. Data from the ANTARES neutrino telescope, spanning 1 to 100 TeV, were examined to constrain this neutrino emission across a defined galactic region. Both track and shower events were evaluated and compared against background estimates derived from an off-zone region. The energy distributions within the search area show an excess over the expected background at approximately a 96 percent confidence level. This observed signal aligns with a power-law neutrino flux featuring a spectral index of 2.45. Furthermore, the signal is consistent with expectations if most of the observed gamma-ray flux from the Galactic Ridge arises from cosmic ray protons and nuclei extending into PeV energies.
Identifying neutrino signals from the inner galaxy helps resolve long-standing questions about the origins of cosmic rays. Because neutrinos are produced alongside gamma rays during proton and nuclei collisions, detecting them confirms the specific particle interactions driving high-energy phenomena in the Milky Way and helps map the energetic mechanisms at work in our galaxy.
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Interactions of cosmic ray protons, atomic nuclei, and electrons in the interstellar medium in the inner part of the Milky Way produce a γ-ray flux from the Galactic Ridge. If the γ-ray emission is dominated by proton and nuclei interactions, a neutrino flux comparable to the γ-ray flux is expected from the same sky region. Data collected by the ANTARES neutrino telescope are used to constrain the neutrino flux from the Galactic Ridge in the 1-100 TeV energy range. Neutrino events reconstructed both as tracks and showers are considered in the analysis and the selection is optimized for the search of an excess in the region |l|<30°, |b|<2°. The expected background in the search region is estimated using an off-zone region with similar sky coverage. Neutrino signal originating from a power-law spectrum with spectral index ranging from Γν=1 to 4 is simulated in both channels. The observed energy distributions are fitted to constrain the neutrino emission from the Ridge. The energy distributions in the signal region are inconsistent with the background expectation at ∼96% confidence level. The mild excess over the background is consistent with a neutrino flux with a power law with a spectral index 2.45−0.34+0.22 and a flux normalization dNνdEν=4.0−2.0+2.7×10−16 GeV−1 cm−2 s−1 sr−1 at 40 TeV reference energy. Such flux is consistent with the expected neutrino signal if the bulk of the observed γ-ray flux from the Galactic Ridge originates from interactions of cosmic ray protons and nuclei with a power-law spectrum extending well into the PeV energy range.
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DOI: 10.1016/j.physletb.2023.137951
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