Speaker
Description
Galactic diffuse gamma-rays emission (GDE) in the sub-PeV energy range (E > 100 TeV = $10^{14}$ eV) was first detected by the Tibet AS$\gamma$ experiment in 2021, ensuring the presence of PeV cosmic-ray accelerators in the Galaxy. On the other hand, in 2023 the Large High Altitude Air Shower Observatory (LHAASO) detected GDE covering an energy range between 10 TeV and 1 PeV. Interestingly, the sub-PeV GDE flux measured by LHAASO from the inner Galactic Plane region ($15^{\circ} < l < 125^{\circ}$ and $|b| < 5^{\circ}$) is lower than that measured by Tibet AS$\gamma$ ($25^{\circ} < l < 100^{\circ}$ and $|b| < 5^{\circ}$) by a factor of five. To study the discrepancy between the results of the two observatories, we estimate the contamination of the Tibet GDE flux from the sub-PeV gamma-ray sources presented in the first LHAASO catalog, accounting for the source masking scheme used in the Tibet GDE analysis. We find that the source contamination of the Tibet GDE flux is less than 30% in the sub-PeV energy range and cannot explain the discrepancy between the Tibet and LHAASO GDE fluxes. Using a GDE theoretical model of Lipari and Vernetto (2018), we also find that the residual discrepancy can be accommodated with the GDE flux from the source masking regions in the LHAASO GDE analysis. Our result supports that the Tibet GDE flux is indeed dominated by GDE and shows some important implications such as a fraction of GDE over the total Galactic sub-PeV gamma-ray emission and significant GDE contamination of the Cygnus Super Bubble.