Observation of photons above 300 TeV associated with a high-energy neutrino from the Cygnus region

TL;DR

This paper reports the first evidence of joint high-energy neutrino and gamma-ray production from a Galactic source, specifically the Cygnus region, indicating cosmic-ray interactions at energies above 300 TeV.

Contribution

It presents the first observation of correlated gamma-ray and neutrino emissions from a Galactic PeVatron, confirming joint production mechanisms.

Findings

Detection of a 3.1-sigma excess of atmospheric air showers from Cygnus.

Observation of a gamma-ray flare above 300 TeV coincident with a neutrino event.

Fluence of gamma-ray flare consistent with neutrino production models.

Abstract

Galactic sites of acceleration of cosmic rays to energies of order 10^15 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 November 2020, 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 3.1-sigma (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.