New Limit On High Galactic Latitude Pev Gamma-Ray Flux From Tibet As Gamma Data

The Tibet AS gamma collaboration has recently reported the detection of gamma-rays with energies up to Peta-electronvolt from parts of the Galactic plane. We note that the analysis of gamma-ray flux by the Tibet-AS gamma experiment also implies an upper bound on the diffuse gamma-ray flux from high Galactic latitudes (|b|> 20 degrees) 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-AS gamma limit on the high Galactic latitude gamma-ray flux in the context of possible mechanisms of multi-messenger (gamma-ray and neutrino) emission from nearby cosmic ray sources, dark matter decays, and the large-scale cosmic ray halo of the Milky Way.