Sub-Threshold Fermi-LAT Sources in the Vicinity of KM3-230312A

Abstract

The KM3NeT collaboration has recently reported the detection of an extraordinary ultra-high-energy neutrino event with an energy of 220 PeV. Ultrahigh energy neutrinos and gamma-rays are co-produced in ultrahigh energy cosmic-ray interactions. The ultrahigh energy gamma-rays produced alongside the KM3NeT neutrino may quickly cascade down to lower energies due to interactions with intergalactic photons and magnetic fields. Because of this, the KM3NeT neutrino could be accompanied by an observable GeV - TeV gamma-ray signal. We investigate the data collected by the Large Area Telescope (LAT) on-board the Gamma-ray Space Telescope for transient and sub-threshold gamma-ray sources in the vicinity of the KM3NeT neutrino. We find three sub-threshold sources with TS ≳16 within 3.5° of the neutrino event not included in any existing LAT catalogs. One of the three, J0616.1-0428, is a transient sub-threshold gamma-ray source that appears only after the neutrino observation, but may be the unrelated flaring of a nearby microquasar. Another sub-threshold source, J0621.1-0610, also exhibits fluctuations in gamma-rays immediately following the neutrino observation, and may be coincident with a radio blazar. We note that the number of sub-threshold sources observed around the KM3NeT neutrino could be expected at another sky region of the same Galactic latitude, and that the fluctuations they exhibit appear to be consistent with background.