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Galactic sites of acceleration of cosmic rays to energies of order 1015 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In 2020 November, the IceCube neutrino observatory reported an ∼150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1σ (post-trial) excess of atmospheric air showers from the same direction, observed by the Carpet–2 experiment and consistent with a few months flare in photons above 300 TeV, in temporal coincidence with the neutrino event. The fluence of the gamma-ray flare is of the same order as that expected from the neutrino observation, assuming the standard mechanism of neutrino production. This is the first evidence for the joint production of high-energy neutrinos and gamma-rays in a Galactic source.

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The γ-ray spectrum of the source HAWC J1825-134 measured with the High Altitude Water Cherenkov (HAWC) observatory extends beyond 200 TeV without any evidence for a steepening or cutoff. There are some indications that the γ-rays detected with HAWC were produced by cosmic-ray protons or nuclei colliding with the ambient gas. Assuming primary protons, we inquire which shape of the primary proton spectrum is compatible with the HAWC measurements. We find that the primary proton spectrum with the power-law shape of γ p = 2.2 and the cutoff energy E c−p > 500 TeV describes the data well. However, much harder spectra with γ p down to 1.3 and E c−p as low as 200 TeV also do not contradict the HAWC measurements. The former option might be realized if the accelerator is inside or very near to the γ-ray production zone. The latter option is viable for the case of a cosmic-ray source that effectively confines low-energy (E p < 10 TeV) accelerated protons. Using publicly available data of the Fermi-LAT space γ-ray telescope, we derive upper limits on the intensity of the HAWC J1825-134 source in the 1 GeV–1 TeV energy range. We show that the account of these upper limits drastically changes the interpretation: only hard (γ p < 1.7) spectra describe the combined HAWC and Fermi-LAT data sets well.