Contribution of Unresolved Sources to Diffuse Gamma-Ray Emission from the Galactic Plane

TL;DR

This paper investigates how unresolved gamma-ray sources contribute to the diffuse emission in the Milky Way, using LHAASO data and a non-parametric source count distribution method, revealing regional differences in source contributions.

Contribution

It introduces a non-parametric approach to estimate unresolved source contributions to diffuse gamma-ray emission using LHAASO data, highlighting regional variations.

Findings

Unresolved sources significantly contribute to outer Galactic diffuse emission.

Model predictions align with observations in the outer Galaxy.

Inner Galaxy requires additional components beyond unresolved sources.

Abstract

The diffuse gamma-ray emission from the Milky Way serves as a crucial probe for understanding the propagation and interactions of cosmic rays within our galaxy. The Galactic diffuse gamma-ray emission between 10 TeV and 1 PeV has been recently measured by the square kilometer array (KM2A) of the Large High Altitude Air Shower Observatory (LHAASO). The flux is higher than predicted for cosmic rays interacting with the interstellar medium. In this work, we utilize a non-parametric method to derive the source count distribution using the published first LHAASO source catalog. Based on this distribution, we calculate the contribution of unresolved sources to the diffuse emission measured by KM2A. When comparing our results to the measured diffuse gamma-ray emission, we demonstrate that for the outer Galactic region, the contributions from unresolved sources and those predicted by models are roughly consistent with experimental observations within the uncertainty. However, for the inner Galactic region, additional components are required to account for the observed data.