Speaker
Description
Cosmic rays (CRs) interact with turbulent magnetic fields in the interstellar medium (ISM), generating non-thermal emission. Recent ultra-high-energy gamma-ray (UHEGR) observations by LHAASO, linked to star-forming regions in the ISM, have introduced new challenges in understanding CR acceleration and propagation in these environments. Despite decades of study, the diffusion of CRs within the sources and the ISM remains a major theoretical challenge. We combined 3D magnetohydrodynamic (MHD) simulations of star-forming regions with test particle simulations to investigate CR diffusion, focusing on the role of mirror diffusion and its interplay with standard resonant scattering diffusion. Our results indicate that mirror diffusion plays a crucial role in regulating CR transport parallel to the magnetic field, leading to significantly slower overall diffusion. Our simulations indicate a diffusion coefficient of ∼10^{27}cm^2/s for particles with energies of a few hundred TeV within a few parsecs of their source - 10 to 100 times smaller than standard predictions. This finding aligns with the UHEGR observations, which require suppressed CR diffusion in localized regions. Additionally, we present results from 3D Monte Carlo simulations of CR cascading within a massive stellar cluster environment, derived from a 3D MHD simulation, where CR diffusion incorporates both mirroring and scattering. These systems are prime candidates for explaining the origin of observed UHEGRs in the Galaxy, and we will present the resulting integrated gamma-ray flux from our simulations.
