Polarised radio synchrotron emission from interstellar, intracluster and intergalactic magnetic fields is affected by frequency-dependent Faraday depolarisation. The maximum polarised intensity depends on the physical properties of the depolarising medium. New-generation radio telescopes like LOFAR, SKA and its precursors need a wide range of frequencies to cover the full range of objects. The optimum frequency of maximum polarised intensity (PI) is computed for the cases of depolarisation in magneto-ionic media by regular magnetic fields (differential Faraday rotation) or by turbulent magnetic fields (internal or external Faraday dispersion), assuming that the Faraday spectrum of the medium is dominated by one component or that the medium is turbulent. Polarised emission from bright galaxy disks, spiral arms and cores of galaxy clusters are best observed at wavelengths below a few centimeters (at frequencies beyond about 10 GHz), halos of galaxies and clusters around decimeter wavelengths (at frequencies below about 2 GHz). Intergalactic filaments need observations at meter wavelengths (frequencies below 300 MHz). Sources with extremely large intrinsic $|RM|$ or RM dispersion can be searched with mm-wave telescopes. Measurement of the PI spectrum allows us to derive the average Faraday rotation measure $|RM|$ or the Faraday dispersion within the source, as demonstrated for the case of the spiral galaxy NGC 6946. Periodic fluctuations in PI at low frequencies are a signature of differential Faraday rotation. Internal and external Faraday dispersion can be distinguished by the different slopes of the PI spectrum at low frequencies. A wide band around the optimum frequency is important to distinguish between varieties of depolarisation effects.
Spectropolarimetry with the Giant Metrewave Radio Telescope at 610 MHz: a case study of two Southern Compact Group fields
我们目前610兆赫的光谱偏振图像从巨型米波射电望远镜（GMRT）。我们详细讨论了GMRT的全偏振模式的属性，并提供了仪器的偏振性能的技术表征。我们表明，该望远镜可用于宽视场分光偏振。旋转测量合成的应用导致在法拉第空间中的几十微焦的水平的灵敏度。作为该仪器的能力的演示，我们提出了两个南方契约组-鹤四重奏和USCG S 063的意见。观测结果与其他无线电和红外数据进行了比较，以限制组成员的光谱指数，偏振分数和法拉第深度。无线电连续辐射是从天鹤座四重奏中的所有四个星系和USCG S 063中的一个星系中检测到的。线性偏振是从NGC 7552的环核星暴环，NGC 7582的活动核和三个扩展的射电星系在天鹤座四重奏场的背景中检测到的。这些背景源允许分类FR-I和X形射电星系。没有证据表明，在任何星系群与群内介质的相互作用。
Radio polarimetry of compact steep spectrum sources at sub-arcsecond resolution
目的-我们报告新的甚大阵列极化观测紧凑陡谱（CSS）源在8.4，15和23 GHz。方法-使用多频VLA观测，我们得出了总强度，偏振和旋转测量（RM）分布的亚弧秒分辨率图像。结果标题-我们提出的CSS源的多频VLA偏振观测。即使在0.1x0.1角秒的分辨率下，也有大约一半的源是点状的。其余的来源有双重或三重结构。CSS源中偏振发射的百分比的低值被确认。平均而言，类星体比星系更极化。已经测量了广泛的RM值。有明确的迹象表明，RM非常大，高达5\,585 rad m**（-2）。CSS星系的特征是RM值大于CSS类星体。大多数物体显示出非常大的RM值。结论-亚弧秒尺度的CSS源的静止框架RM估计的可用数据表明，这些值有很大的范围，可扩展到约36，000 rad m**（-2）。RM估计表明磁离子介质的整体密度大于经典射电源。
Faraday Complexity and Depolarisation in a High-Rotation-Measure Radio Galaxy from the Spectra and Polarisation In Cutouts of Extragalactic Sources (SPICE-RACS) DR2
Indian Institute of Engineering Science and Technology（印度工程科学与技术学院）；Banwarilal Bhalotia College（班瓦里拉尔·巴洛蒂亚学院）
The diffuse radio emission in the high-redshift cluster PSZ2 G091.83+26.11: total intensity and polarisation analysis with Very Large Array 1-4 GHz observations
本文利用 VLA 1–4 GHz 及多波段射电和 Chandra X 射线数据，研究高红移星系团 PSZ2G091.83+26.11 中的拉长弥散射电源，确认其为射电遗迹，并通过谱指数、偏振和磁场方向揭示其由并合激波压缩形成，提出该星系团可能处于年轻并合阶段。
