用EHT偏振测量探测银心吸积Turbulence
Probing Accretion Turbulence in the Galactic Center with EHT Polarimetry
摘要：
由微分旋转驱动的不稳定性产生的磁场被认为是黑洞吸积的关键。这些不稳定性在湍流状态下饱和;因此，人马座A*（Sgr A*）的视界分辨图像的空间和时间变化将能够凭经验评估吸积理论的这一关键方面。然而，星际散射模糊了银河系中心的高频无线电图像，并引入了虚假的小尺度结构，使图像中空间波动的解释变得复杂。我们探索星际散射对Sgr A* 偏振图像的影响，并证明了对于可靠的物理参数，干涉散射是非双折射的。因此，我们构建了一个散射缓解方案，利用地平线解决极化毫米/亚毫米VLBI观测产生的内在空间波动的统计措施，因此底层吸积流湍流。一个最佳的极化基础被确定，对应于在三维空间中的磁场取向的波动的测量。我们使用模拟数据集验证我们的缓解方案，并发现当前和未来的地面实验将很容易能够准确地测量图像波动功率谱。
英文摘要：
Magnetic fields grown by instabilities driven by differential rotation are believed to be essential to accretion onto black holes. These instabilities saturate in a turbulent state; therefore, the spatial and temporal variability in the horizon-resolving images of Sagittarius A* (Sgr A*) will be able to empirically assess this critical aspect of accretion theory. However, interstellar scattering blurs high-frequency radio images from the Galactic center and introduces spurious small-scale structures, complicating the interpretation of spatial fluctuations in the image. We explore the impact of interstellar scattering on the polarized images of Sgr A* and demonstrate that for credible physical parameters, the intervening scattering is non-birefringent. Therefore, we construct a scattering mitigation scheme that exploits horizon-resolving polarized millimeter/submillimeter VLBI observations to generate statistical measures of the intrinsic spatial fluctuations and therefore the underlying accretion flow turbulence. An optimal polarization basis is identified, corresponding to measurements of the fluctuations in magnetic field orientation in three dimensions. We validate our mitigation scheme using simulated data sets and find that current and future ground-based experiments will readily be able to accurately measure the image-fluctuation power spectrum.
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