New limit on high Galactic latitude PeV γ-ray flux from Tibet ASγ data

The Tibet ASγ collaboration has recently reported the detection of γ -rays with energies up to Peta-electronvolt from parts of the Galactic plane. We note that the analysis of γ -ray flux by the Tibet-ASγ experiment also implies an upper bound on the diffuse γ -ray flux from high Galactic latitudes (|b |> 20°) in the energy range between 100 TeV and 1 PeV. This bound is up to an order of magnitude stronger than previously derived bounds from GRAPES3, KASCADE, and CASA-MIA experiments. We discuss the new Tibet-ASγ limit on the high Galactic latitude γ -ray flux in the context of possible mechanisms of multi-messenger (γ -ray and neutrino) emission from nearby cosmic ray sources, dark matter decays, and the large-scale cosmic ray halo of the Milky Way.