Standard self-confinement and extrinsic turbulence models for cosmic ray transport are fundamentally incompatible with observations
Standard self-confinement and extrinsic turbulence models for cosmic ray transport are fundamentally incompatible with observations
复制标题
宇宙射线传输的标准自约束和外在湍流模型从根本上与观测不相容
DOI：
10.1093/mnras/stac2909
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发表时间：
2022
影响因子：
4.8
通讯作者：
Ji, Suoqing
中科院分区：
文献类型：
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作者：
Hopkins, Philip F.;Squire, Jonathan;Butsky, Iryna S.;Ji, Suoqing
宇宙线（CR）动力学的模型从根本上取决于CR散射率的磁波动。在ISM中，对于能量为MeV-TeV的CR，这些波动通常归因于“非本征湍流”（ET）-来自较大尺度的级联-或“自约束”（SC）-CR流的自生成波动。使用简单的分析参数和详细的“活”数值CR运输计算在星系模拟中，我们表明，这两个，在标准的形式，甚至不能解释所观察到的CR光谱的基本定性特征。对于ET，任何频谱，遵守临界平衡或功能现实的各向异性，或任何频谱，占有限阻尼低于耗散尺度，预测定性不正确的频谱形状和缩放的B/C和其他物种。即使以某种方式忽略了各向异性和阻尼，观测所需的散射率不同意ET预测的数量级。对于SC，驱动对CR能量密度的依赖性意味着几乎不可能恢复观察到的CR谱形状和缩放，并且再次存在数量级归一化问题。但更严重的是，具有超Alfvénic流的SC解决方案是不稳定的。在现场模拟中，他们要么恢复到任意快速的CR逃逸，二次生产为零，要么恢复到具有太强的CR约束和二次生产的瓶颈解决方案。解决这些根本问题而不放弃基本的等离子体过程需要调用不同的散射波动的驱动程序。这些必须在广泛的尺度上起作用，功率谱服从几个特定的（但似乎合理的）约束。
Models for cosmic ray (CR) dynamics fundamentally depend on the rate of CR scattering from magnetic fluctuations. In the ISM, for CRs with energies ∼MeV-TeV, these fluctuations are usually attributed either to ‘extrinsic turbulence’ (ET) – a cascade from larger scales – or ‘self-confinement’ (SC) – self-generated fluctuations from CR streaming. Using simple analytic arguments and detailed ‘live’ numerical CR transport calculations in galaxy simulations, we show that both of these, in standard form, cannot explain even basic qualitative features of observed CR spectra. For ET, any spectrum that obeys critical balance or features realistic anisotropy, or any spectrum that accounts for finite damping below the dissipation scale, predicts qualitatively incorrect spectral shapes and scalings of B/C and other species. Even if somehow one ignored both anisotropy and damping, observationally required scattering rates disagree with ET predictions by orders of magnitude. For SC, the dependence of driving on CR energy density means that it is nearly impossible to recover observed CR spectral shapes and scalings, and again there is an orders-of-magnitude normalization problem. But more severely, SC solutions with super-Alfvénic streaming are unstable. In live simulations, they revert to either arbitrarily rapid CR escape with zero secondary production, or to bottleneck solutions with far-too-strong CR confinement and secondary production. Resolving these fundamental issues without discarding basic plasma processes requires invoking different drivers for scattering fluctuations. These must act on a broad range of scales with a power spectrum obeying several specific (but plausible) constraints.