Messier 87* 模拟线偏振图像中的光子环对称性
Photon Ring Symmetries in Simulated Linear Polarization Images of Messier 87*
摘要：
事件视界望远镜（EHT）最近发布了第一张关于超大质量黑洞Messier 87*（以下简称\m{}）周围吸积流的线偏振图像。在EHT图像中发现的螺旋偏振模式有利于磁制动盘（MAD）作为EHT图像的解释。随着下一代甚长基线干涉测量（VLBI）的改进，理解被称为“光子环”的高度透镜结构中的类似偏振特征，光子在到达观察者之前围绕黑洞进行多个半轨道，这对分析未来的图像至关重要。最近的工作表明，相对于更直接的发射，这个图像区域可能是去偏振的。我们通过分解\m{}吸积系统EHT模拟图像库中的光子半轨道来扩展这一观察，发现MAD模拟图像显示光子环的相对去极化归因于相反螺旋电场矢量的相消干涉;这种反对称性，纯粹是由强引力透镜引起的，可以在光子环区域中相对于直接图像产生高达${\sim}50\%$的去偏振。在系统中，没有磁逮捕，并与高自旋和离子和电子的相同温度的系统除外，我们发现，高度透镜的间接子图像几乎完全去极化，造成适度的去极化的光子环区域在完整的图像。我们预测，下一代EHT观测\m{}极化应共同约束黑洞自旋和底层的发射和磁场几何。
英文摘要：
The Event Horizon Telescope (EHT) recently released the first linearly polarized images of the accretion flow around the supermassive black hole Messier 87*, hereafter \m{}. The spiraling polarization pattern found in EHT images favored magnetically arrested disks (MADs) as the explanation for the EHT image. With next-generation improvements to very long baseline interferometry (VLBI) on the horizon, understanding similar polarized features in the highly lensed structure known as the "photon ring," where photons make multiple half-orbits about the black hole before reaching the observer, will be critical to analysis of future images. Recent work has indicated that this image region may be depolarized relative to more direct emission. We expand this observation by decomposing photon half-orbits in the EHT library of simulated images of the \m{} accretion system and find that images of MAD simulations show a relative depolarization of the photon ring attributable to destructive interference of oppositely spiraling electric field vectors; this antisymmetry, which arises purely from strong gravitational lensing, can produce up to ${\sim}50\%$ depolarization in the photon ring region with respect to the direct image. In systems that are not magnetically arrested and with the exception of systems with high spin and ions and electrons of equal temperature, we find that highly lensed indirect sub-images are almost completely depolarized, causing a modest depolarization of the photon ring region in the complete image. We predict that next-generation EHT observations of \m{} polarization should jointly constrain the black hole spin and the underlying emission and magnetic field geometry.
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