Black hole magnetic fields and their imprint on circular polarization images
Black hole magnetic fields and their imprint on circular polarization images
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DOI：
10.1093/mnras/stab1289
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
Angelo Ricarte;R. Qiu;R. Narayan
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文献类型：
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作者：
Angelo Ricarte;R. Qiu;R. Narayan
黑洞吸积流的圆极化可以编码底层磁场结构的特性。利用广义相对论磁流体动力学 (GRMHD) 模拟，我们研究了事件视界望远镜 (EHT) 可能观测到的圆偏振图像上磁场几何形状的印记。我们将图像分解为在这些模型中产生圆偏振的不同机制，这些模型对视线方向和磁场扭曲都很敏感。在这些模型中，如在多个源中观察到的那样，圆偏振随时间的稳定迹象可归因于这些特性的稳定性。我们说明了通用螺旋磁场几何形状的不同方面如何印在圆偏振图像上。我们还发现了光弯曲的新效应，它会影响事件视界尺度上的圆偏振图像。一个结果是面对面系统中连续光子环的符号翻转，如果法拉第旋转可观察到并且未被法拉第旋转破坏，则可以直接编码接近磁场的旋向性。
The circular polarization of black hole accretion flows can encode properties of the underlying magnetic field structure. Using general relativistic magnetohydrodynamics (GRMHD) simulations, we study the imprint of magnetic field geometry on circular polarization images potentially observable by the Event Horizon Telescope (EHT). We decompose images into the different mechanisms that generate circular polarization in these models, which are sensitive to both the line of sight direction and twist of the magnetic field. In these models, a stable sign of the circular polarization over time, as observed for several sources, can be attributed to a stability of these properties. We illustrate how different aspects of a generic helical magnetic field geometry become imprinted on a circular polarization image. We also identify novel effects of light bending that affect the circular polarization image on event horizon scales. One consequence is the sign flipping of successive photon rings in face-on systems, which if observable and uncorrupted by Faraday rotation, can directly encode the handedness of the approaching magnetic field.