Observation of AGILE transient γ-ray sources in coincidence with cosmic neutrino events

The origin of the diffuse flux of very high-energy cosmic neutrinos above TeV energies observed by the IceCube experiment at the South Pole is still largely unknown. Simultaneous multi-frequency observations of the uncertainty location regions of these cosmic neutrinos are needed to identify the possible electromagnetic counterpart. Since 2016, the IceCube collaboration alerts almost in real time the astronomical community whenever a clear signature of a neutrino-induced event is recorded. The AGILE γ -ray satellite is fully involved in this multi-messenger hunt for cosmic neutrino sources. Using data obtained by the γ -ray imager onboard of the satellite, we searched for transient gamma-ray sources above 100 MeV that are temporally and spatially coincident with recent high-energy neutrino IceCube events. We find three AGILE candidate sources that can be considered as possible counterparts to neutrino events. The chance probability of this association is shown to be very low. One of the sources detected by AGILE in γ rays is the blazar TXS 0506+056, recently suggested as the first most likely extra-galactic emitter of TeV neutrinos. For the other two gamma-ray sources there are no obvious known counterparts, and both galactic and extragalactic origin should be considered.