AI 中文总结
本研究结合磁流体模拟与宇宙线传播计算，验证磁镜加散射的慢扩散机制可解释大质量年轻星团的甚高能伽马射线辐射，指出扩散模式而非源位置决定辐射特征。
AI 中文摘要
近年来，对能够将宇宙线（CRs）加速到PeV能量的银河系源的搜寻工作取得了显著进展。LHAASO等高能观测台在多个源周围探测到了延展的伽马射线晕，表明宇宙线以异常缓慢的扩散方式从其加速位点逃逸。理论研究提出，磁镜扩散结合湍流中的投掷角散射可以自然地抑制宇宙线的输运。\n本文首先展示了磁镜扩散结合散射如何抑制宇宙线输运，从而产生与能量相关的扩散系数$D(E)\propto E^{1/3}$。随后，我们将大质量年轻星团（YMSC）的三维磁流体动力学（MHD）模拟与蒙特卡洛宇宙线传播计算程序CRPropa相结合。该模型包含了背景气体密度、磁场、恒星黑体辐射与尘埃辐射、宇宙微波背景以及银河系星际辐射场。\n我们以YMSC W43为基准，对比了两种宇宙线注入几何构型：中心源构型，以及代表星团集体风激波的球壳构型。研究表明，满足$D(E)\propto E^{1/3}$的磁镜+散射扩散，结合$E^{-2}$的宇宙线注入谱，能够重现Fermi和LHAASO观测到的伽马射线谱。相比之下，能量依赖性更强的扩散需要更硬的宇宙线注入谱（约$E^{-1.6}$）才能匹配观测数据。轻子型逆康普顿辐射与强子型辐射的相对贡献对扩散区域极为敏感。最后，所得谱线对宇宙线注入位置的依赖性很小，仅中心源情形下注入光度更低。总体而言，我们的结果表明，观测到的伽马射线辐射主要由扩散传播区域决定，而非宇宙线源的精确位置。
英文摘要
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.
