Cosmic Ray Diffusion and the Origin of Very High Energy Gamma-Ray Emission in Young Massive Stellar Clusters

[2608.14547] Cosmic Ray Diffusion and the Origin of Very High Energy Gamma-Ray Emission in Young Massive Stellar Clusters Skip to main content Search Submit Donate Log in Search arXiv Press Enter to search · Advanced search Astrophysics > High Energy Astrophysical Phenomena arXiv:2608.14547 (astro-ph) [Submitted on 14 Aug 2026] Title: Cosmic Ray Diffusion and the Origin of Very High Energy Gamma-Ray Emission in Young Massive Stellar Clusters Authors: Lucas Barreto-Mota , Elisabete M. de Gouveia Dal Pino , Gaetano Di Marco , Rafael Alves Batista , Stela Adduci Faria View a PDF of the paper titled Cosmic Ray Diffusion and the Origin of Very High Energy Gamma-Ray Emission in Young Massive Stellar Clusters, by Lucas Barreto-Mota and 4 other authors View PDF HTML (experimental) Abstract: The search for Galactic sources capable of accelerating cosmic rays (CRs) to PeV energies has advanced significantly in recent years. High-energy observatories such as LHAASO have detected extended gamma-ray halos around several sources, suggesting that CRs escape their acceleration sites through anomalously slow diffusion. Theoretical studies propose that magnetic mirror diffusion combined with pitch-angle scattering in turbulent flow can naturally suppress CR transport. Here, we first show how mirror diffusion combined with scattering suppresses cosmic-ray transport, leading to an energy-dependent diffusion coefficient $D(E)\propto E^{1/3}$. We then combine a 3D magnetohydrodynamic (MHD) simulation of a young massive stellar cluster (YMSC) with Monte Carlo CR propagation calculations (CRPropa). The model includes the background gas density, magnetic field, stellar blackbody and dust emission, the cosmic microwave background, and the Galactic interstellar radiation field. Using the YMSC W43 as a benchmark, we compare two CR injection geometries: a central source and a spherical shell representing the cluster's collective wind shock. We show that mirror+scattering diffusion $D(E)\propto E^{1/3}$, combined with a CR injection spectrum $E^{-2}$, reproduces the gamma-ray spectrum observed by Fermi and LHAASO. In contrast, stronger energy-dependent diffusion requires a harder CR injection spectrum, $\sim E^{-1.6}$, to match the data. The relative contributions of leptonic inverse-Compton and hadronic emission depend sensitively on the diffusion regime. Finally, the resulting spectra show little dependence on the CR injection location, aside from a lower injection luminosity in the central-source case. Overall, our results indicate that the observed gamma-ray emission is shaped primarily by the diffusive propagation regime rather than by the precise location of the CR source. Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) Cite as: arXiv:2608.14547 [astro-ph.HE] (or arXiv:2608.14547v1 [astro-ph.HE] for this version) https://doi.org/10.48550/arXiv.2608.14547 Focus to learn more arXiv-issued DOI via DataCite Submission history From: Lucas Barreto-Mota [ view email ] [v1] Fri, 14 Aug 2026 17:59:15 UTC (931 KB) Full-text links: Access Paper: View a PDF of the paper titled Cosmic Ray Diffusion and the Origin of Very High Energy Gamma-Ray Emission in Young Massive Stellar Clusters, by Lucas Barreto-Mota and 4 other authors View PDF HTML (experimental) TeX Source view license Additional Features Audio Summary Current browse context: astro-ph.HE < prev | next > new | recent | 2026-08 Change to browse by: astro-ph References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar export BibTeX citation Loading... BibTeX formatted citation × loading... 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