AI 中文总结
该研究通过双流体磁流体动力学模拟，发现强超声速、高超阿尔文湍流可在离子-中性粒子阻尼显著时，维持慢且近各向同性的宇宙射线输运，匹配观测推断的扩散系数范围。
AI 中文摘要
扩展的TeV-PeV伽马射线晕观测表明，尽管存在大尺度银河磁场，宇宙射线（CR）的扩散速度仍显著慢于银河平均值且仅具有弱各向异性。我们研究这种输运是否能在部分电离的源环境中产生，其中离子-中性粒子阻尼会消除导致回旋共振散射的小尺度涨落。通过使用包含相对论性测试粒子追踪的双流体磁流体动力学湍流模拟，我们发现，在跨声速湍流中，阻尼使平行扩散系数增加约两个数量级，从而显著增强沿磁场的输运。在超声速湍流中，与激波相关的磁涨落在阻尼后仍能留存，并维持非共振的投掷角散射，使平行扩散系数的增加仅为几倍到十倍。在阿尔文马赫数MA≳5时，磁场方向在阿尔文尺度上退相关，促使平行扩散系数D∥与垂直扩散系数D⊥趋于相等。对于Ms≃10、MA≃5-10以及百TeV伽马射线源环境的代表性参数，我们得到的D∥与D⊥相当，处于观测推断的~10^27-10^28 cm² s⁻¹范围内。这些结果表明，源环境中强超声速、高超阿尔文湍流即使在离子-中性粒子阻尼效应显著时，也能维持慢且近各向同性的CR输运。
英文摘要
Extended TeV-PeV gamma-ray halo observations imply cosmic-ray (CR) diffusion that is both substantially slower than the Galactic mean and only weakly anisotropic, despite the presence of a large-scale Galactic magnetic field. We investigate whether such transport can arise in partially ionized source environments, where ion-neutral damping removes the small-scale fluctuations responsible for gyroresonant scattering. Using two-fluid magnetohydrodynamic turbulence simulations with relativistic test-particle tracking, we find that damping increases the parallel diffusion coefficient by approximately two orders of magnitude in trans-sonic turbulence, thereby strongly enhancing field-aligned transport. In supersonic turbulence, shock-associated magnetic fluctuations survive the damping and sustain non-resonant pitch-angle scattering, limiting the increase in parallel diffusion to a factor of a few to ten. At high Alfvénic Mach numbers, $M_A\gtrsim5$, the magnetic-field direction decorrelates over the Alfvén scale, driving parallel diffusion coefficient $D_\parallel$ and perpendicular diffusion coefficient $D_\perp$ toward equality. For $M_s\simeq10$, $M_A\simeq5$-$10$, and representative parameters for hundred-TeV gamma-ray source environments, we obtain comparable $D_\parallel$ and $D_\perp$, within the observationally inferred range of $\sim10^{27}$-$10^{28}\,\mathrm{cm^2\,s^{-1}}$. These results show that strongly supersonic, highly super-Alfvénic turbulence in source environments can sustain slow, nearly isotropic CR transport even when the ion-neutral damping effect is important.
Comments10 pages, 6 figures, accepted for publication in ApJL
