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

A Neronov,Ie Vovk,D Semikoz

doi:10.1051/0004-6361/202141800

Abstract

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.

Highlights

Diffuse GeV–TeV γ-ray flux from the sky is dominated by emission from interactions of cosmic rays in the interstellar medium (Ackermann et al 2012; Acero et al 2016; Lipari & Vernetto 2018; Neronov & Semikoz 2020)
We note that the analysis of γ-ray flux by the Tibet-ASγ experiment 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
In the energy range below several hundred Giga-electronvolts, high Galactic latitude diffuse flux has a sizeable contribution from extragalactic sources, but this contribution vanishes at higher energies because of the effect of absorption of extragalactic γ-rays during their propagation through the intergalactic medium (Gould & Schréder 1967; Franceschini et al 2008)

Summary

Introduction

Diffuse GeV–TeV γ-ray flux from the sky is dominated by emission from interactions of cosmic rays in the interstellar medium (Ackermann et al 2012; Acero et al 2016; Lipari & Vernetto 2018; Neronov & Semikoz 2020). High Galactic latitude flux has been measured up to several Tera-electronvolts in energy by the Fermi/LAT telescope (Neronov & Semikoz 2020) It is dominated by emission from the local interstellar medium, but can contain contributions from nearby very extended sources (Neronov et al 2018; Bouyahiaoui et al 2019). Diffuse γ-ray flux has been measured from parts of the sky by extensive air shower (EAS) arrays MILAGO, HAWC, and ARGO-YBJ (Abdo et al.2008; Bartoli et al 2015; Abeysekara et al 2017a) In this energy range, emission from the Galactic plane generally follows the powerlaw extrapolation of the lower energy flux (Neronov & Semikoz 2020), as expected from the flux produced by the cosmic rays with a powerlaw spectrum. An upper limit on the high Galactic latitude flux from the Tibet-ASγ measurements and explore its implications for models of high-energy particle acceleration in the Milky Way and for the models of super-heavy dark matter

Tibet-ASγ limit on the high Galactic latitude γ-ray flux

Findings

Implications of the revised bound