Spectrum and Anisotropy of Turbulence from Multi-Frequency Measurement of Synchrotron Polarization

TL;DR

This paper develops a statistical framework to analyze turbulence in synchrotron-emitting media using polarization fluctuations across frequencies and spatial separations, enabling extraction of turbulence properties and magnetic field orientation.

Contribution

The authors introduce new measures for spectral slopes and correlation scales of magnetic turbulence and Faraday rotation, applicable to sparse interferometric data and various emission scenarios.

Findings

Methods to determine turbulence spectral slopes and correlation scales.

Techniques to infer magnetic field anisotropy and 3D orientation.

Applicability to existing and future large-scale radio data sets.

Abstract

We consider turbulent synchrotron emitting media that also exhibits Faraday rotation and provide a statistical description of synchrotron polarization fluctuations. In particular, we consider these fluctuations as a function of the spatial separation of the direction of measurements and as a function of wavelength for the same line-of-sight. On the basis of our general analytical approach, we introduce several measures that can be used to obtain the spectral slopes and correlation scales of both the underlying magnetic turbulence responsible for emission and the spectrum of the Faraday rotation fluctuations. We show the synergetic nature of these measures and discuss how the study can be performed using sparsely sampled interferometric data. We also discuss how additional characteristics of turbulence can be obtained, including the turbulence anisotropy, the three dimensional direction of the mean magnetic field. We consider both cases when the synchrotron emission and Faraday rotation regions coincide and when they are spatially separated. Appealing to our earlier study in Lazarian and Pogosyan (2012) we explain that our new results are applicable to a wide range of spectral indexes of relativistic electrons responsible for synchrotron emission. We expect wide application of our techniques both with existing synchrotron data sets as well as with big forthcoming data sets from LOFAR and SKA.