Quantitative constraint on the source contribution to the Galactic diffuse gamma rays detected by the Tibet air shower array

TL;DR

This study constrains the contribution of unresolved gamma-ray sources to the Galactic diffuse gamma-ray background above 398 TeV, indicating most high-energy diffuse events are genuinely diffuse rather than source-related.

Contribution

It provides a quantitative upper limit on unresolved source contributions to high-energy diffuse gamma rays using Tibet and LHAASO data, a novel multi-instrument analysis.

Findings

Unresolved sources contribute less than 31% above 398 TeV.

No diffuse events above 398 TeV originate from newly detected sources.

Most diffuse gamma-ray events are of truly diffusive origin.

Abstract

The fraction of the contribution from yet-unresolved gamma-ray sources in the Galactic diffuse gamma rays observed by the Tibet air shower array is an important key to interpreting recent multi-messenger observations. This paper shows a surprising fact: no Tibet diffuse events above 398TeV come from the gamma-ray sources newly detected above 100 TeV by LHAASO. Based on this observational fact, the contribution of sources unresolved by LHAASO to the Tibet diffuse events is estimated to be less than 31% above 398TeV with a 99% confidence level. Our result shows that unresolved sources make only a sub-dominant contribution to the Tibet diffuse events above 398 TeV and a large fraction of the events are truly a diffusive nature.