The magnetic power spectrum in Faraday rotation screens
The magnetic power spectrum in Faraday rotation screens
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法拉第旋转屏中的磁功率谱
DOI：
10.1051/0004-6361:20030172
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发表时间：
2003
影响因子：
6.5
通讯作者：
C. Vogt
中科院分区：
文献类型：
--
作者：
T. Ensslin;C. Vogt
扩展背景射电源的旋转测量（RM）图的自相关函数和类似的傅立叶功率谱可以用于测量前景法拉第屏内的磁自相关和功率谱张量的分量。在各向同性磁场分布统计的情况下，可以重建该张量的完整非螺旋部分。螺旋部分只能通过附加信息来访问;例如，场是无力的知识。磁场强度、能谱和自相关长度$\lambda_B$可以单独从非螺旋部分获得。我们证明，$\lambda_B$可以从$\lambda_{RM}$，观察上容易获得的RM映射的自相关长度有很大的不同。在典型的天体物理情况下，$\lambda_{RM}> \lambda_B$。任何不考虑这种区别的RM研究都可能低估了磁场强度。对于幂律磁功率谱，并为补丁磁场配置的中心RM自相关函数示出具有特征渐近形状。讨论了如何限制斑片状场分布的体积填充因子。我们讨论的策略来分析观测数据，考虑到-与窗口函数的帮助下-有限的范围内的极化射电源，空间分布的电子密度和平均磁能密度在屏幕上，并允许降噪数据加权。我们简要地讨论了可能的观测伪影的影响，以及避免它们的策略。
The autocorrelation function and similarly the Fourier-power spectrum of a rotation measure ( RM ) map of an extended background radio source can be used to measure components of the magnetic autocorrelation and power-spectrum tensor within a foreground Faraday screen. It is possible to reconstruct the full non-helical part of this tensor in the case of an isotropic magnetic field distribution statistics. The helical part is only accessible with additional information; e.g. the knowledge that the fields are force-free. The magnetic field strength, energy spectrum and autocorrelation length $\lambda_B$ can be obtained from the non-helical part alone. We demonstrate that $\lambda_B$ can differ substantially from $\lambda_{RM}$, the observationally easily accessible autocorrelation length of an RM map. In typical astrophysical situation $\lambda_{RM}> \lambda_B$. Any RM study, which does not take this distinction into account, likely underestimates the magnetic field strength. For power-law magnetic power spectra, and for patchy magnetic field configurations the central RM autocorrelation function is shown to have characteristic asymptotic shapes. Ways to constrain the volume filling factor of a patchy field distribution are discussed. We discuss strategies to analyse observational data, taking into account – with the help of a window function – the limited extent of the polarised radio source, the spatial distribution of the electron density and average magnetic energy density in the screen, and allowing for noise reducing data weighting. We briefly discuss the effects of possible observational artefacts, and strategies to avoid them.
影响因子：
1.3
作者：
R. Wielebinski
通讯作者：
R. Wielebinski