Studying the Properties of Compressible Magnetohydrodynamic Turbulence Using Synchrotron Fluctuation Statistics
Studying the Properties of Compressible Magnetohydrodynamic Turbulence Using Synchrotron Fluctuation Statistics
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DOI：
10.3847/1538-4357/ac9d31
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发表时间：
2022-10
期刊：
影响因子：
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通讯作者：
Ru-Yue Wang;Jianfu Zhang;A. Lazarian;H. Xiao;F. Xiang
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作者：
Ru-Yue Wang;Jianfu Zhang;A. Lazarian;H. Xiao;F. Xiang
基于3DMHD数值模拟的合成同步加速器观测数据，研究了可压缩磁流体(MHD)湍流在不同湍流状态下的可观测特性。利用同步辐射发射率和强度，我们首先利用归一化关联函数研究了宇宙线光谱指数对湍流性质测量的影响。然后，我们研究了由三个基本MHD模产生的同步加速器总强度和偏振强度的各向异性如何随视角，即平均磁场与视线之间的夹角而变化。为此，我们采用四极矩与单极矩之比(QM)。数值结果表明：(1)对于任意的宇宙线谱指数，同步加速器统计的两点关联函数与磁场指数γ=2的特例有关，与Lazarian&Pogosyan给出的解析公式一致：(2)由Alfvén模和慢模引起的同步加速器总强度和偏振强度的各向异性随视角的增大而增大，而快模的各向异性几乎不随视角的变化而增加；(3)用于研究湍流的同步加速器强度的解析公式可以用来描述偏振强度的统计特性，而QM可以成功地恢复湍流的各向异性。这项研究验证了Lazarian&Pogosyan的分析方法，并开辟了一条从观测研究湍流的途径。
We study the observable properties of compressible magnetohydrodynamic (MHD) turbulence covering different turbulence regimes, based on synthetic synchrotron observations arising from 3D MHD numerical simulations. Using the synchrotron emissivity and intensity, we first explore how the cosmic-ray spectral indices affect the measurements of the turbulence properties by employing normalized correlation functions. We then study how the anisotropy of the synchrotron total and polarization intensities arising from the three fundamental MHD modes varies with the viewing angle, i.e., the angle between the mean magnetic field and the line of sight. We employ the ratio of the quadrupole moment to the monopole moment (QM) for this purpose. Our numerical results demonstrate that: (1) the two-point correlation function of synchrotron statistics for the arbitrary cosmic-ray spectral index is related to the special case of the magnetic field index γ = 2, in agreement with the analytical formulae provided by Lazarian & Pogosyan; (2) the anisotropy of the synchrotron total and polarization intensities arising from the Alfvén and slow modes increases with the increase of the viewing angle, while that of fast mode remains almost unchanged with the viewing angle; and (3) the analytical formulae of the synchrotron intensities for studying turbulence can be applied to describe the statistics of the polarization intensities, and the QM can be successfully used to recover the turbulence anisotropy. This study validates the analytical approach of Lazarian & Pogosyan and opens up a way of studying turbulence from observations.