Speaker
Description
Using the 3D simulation option of the GALPROP framework we modelled Galactic cosmic-ray (CR) diffusion utilising a distribution of CR sources stochastically placed in position and time within the Galaxy. This source distribution more accurately represents the formation rates and finite lifetimes compared to the steady-state CR injection models that are typically assumed.
We investigate the time variability of the diffuse gamma-ray emission along the Galactic plane.
Our results show that the leptonic component of the gamma-ray emission is highly sensitive to the assumed electron injection and spectral characteristics. Furthermore, the leptonic component is heavily dependent on the positions of the sources due to the rapid synchrotron cooling of the very-high-energy electrons. As the gamma-ray energy increases so does the magnitude of the variations in the total diffuse flux. At 100 GeV the variations due only to the stochastic nature of the CR electron source placement can be as large as 30 percent in the outer Galaxy, increasing to an order of magnitude at 10 TeV.
Considering the placement of the CR sources is critical in connecting the Galactic diffuse emission across the GeV--PeV regimes. The variations induced by the stochastic CR electron source placement predict emissions consistent with those inferred from the H.E.S.S. Galactic plane survey. Additionally, these variations provide a natural explanation for the observed excess gamma-ray emission measured by LHAASO without ad-hoc tuning of the models.
