用同步辐射偏振仪探测磁性turbulence：Stokes关联函数磁场的统计和结构
Probing magnetic turbulence by synchrotron polarimetry: statistics and structure of magnetic fields from Stokes correlators
摘要：
我们描述了一种基于射电偏振测量数据探测宇宙磁场统计特性的技术。像功率谱这样的二阶磁场统计不能总是区分具有本质上不同的空间结构的磁场。同步辐射偏振测量自然允许从观测数据中推断出某些四阶磁场统计，这提升了这种简并性，从而可以帮助我们更好地了解宇宙场的结构，并测试描述磁湍流的理论场景。在这项工作中，我们表明，四阶相关的物理利益，张力谱，可以恢复从偏振同步辐射数据。我们开发了一个估计这个数量的基础上极化发射观测法拉第旋转自由频率制度。我们考虑两种情况：统计各向同性场分布，统计各向同性场叠加在一个弱平均场。在这两种情况下，张力功率谱是可测量的;在后一种情况下，磁功率谱也可以获得。该方法是精确的，在理想化的情况下，均匀的相对论电子分布，具有幂律能谱与谱指数p=3，并假设统计各向同性的湍流场。我们使用数值模拟磁场产生的合成数据进行测试，我们的方法。我们表明，该方法是有效的，它是不过分敏感的电子光谱指数的值，并观察到的张力谱允许一个区分，例如，随机缠结的磁场（许多研究中的默认假设）和以折叠的通量片或细丝组织的场。
英文摘要：
We describe a technique for probing the statistical properties of cosmic magnetic fields based on radio polarimetry data. Second-order magnetic field statistics like the power spectrum cannot always distinguish between magnetic fields with essentially different spatial structure. Synchrotron polarimetry naturally allows certain 4th-order magnetic field statistics to be inferred from observational data, which lifts this degeneracy and can thereby help us gain a better picture of the structure of the cosmic fields and test theoretical scenarios describing magnetic turbulence. In this work we show that a 4th-order correlator of physical interest, the tension-force spectrum, can be recovered from the polarized synchrotron emission data. We develop an estimator for this quantity based on polarized-emission observations in the Faraday-rotation-free frequency regime. We consider two cases: a statistically isotropic field distribution, and a statistically isotropic field superimposed on a weak mean field. In both cases the tension force power spectrum is measurable; in the latter case, the magnetic power spectrum may also be obtainable. The method is exact in the idealized case of a homogeneous relativistic-electron distribution that has a power-law energy spectrum with a spectral index p=3, and assumes statistical isotropy of the turbulent field. We carry out tests of our method using synthetic data generated from numerically simulated magnetic fields. We show that the method is valid, that it is not prohibitively sensitive to the value of the electron spectral index, and that the observed tension-force spectrum allows one to distinguish between, e.g., a randomly tangled magnetic field (a default assumption in many studies) and a field organized in folded flux sheets or filaments.
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