基于二阶矩正则化的黑洞的VLBI成像
VLBI imaging of black holes via second moment regularization
摘要：
事件视界望远镜（EHT）的成像保真度目前取决于其稀疏的基线覆盖。特别是，EHT覆盖范围主要是由长基线，是高度敏感的大气条件和实验之间的网站损失。有限的短/中距离基线特别影响成像过程，阻碍了图像中更多扩展特征的恢复。我们提出了一个算法的应急缺乏良好的约束短基线在紧凑的源，如超大质量黑洞与EHT观察到的成像。该技术以尺寸约束的形式对重建图像施加特定的二阶矩，该尺寸约束对应于零基线处测量的可见度函数的曲率。该方法能够恢复在短基线上基线覆盖的间隙中丢失的信息，并能够校正观测中提供短基线测量的台站的任何系统振幅偏移。正则化可以使用历史源大小测量来约束重建图像的二阶矩以匹配观察到的大小。我们还表明，一个特征尺寸可以从现有的短基线测量，从其他波长外推，或估计没有互补的尺寸限制与参数搜索。我们证明了这种方法的静态和电影重建的可变源的能力。
英文摘要：
The imaging fidelity of the Event Horizon Telescope (EHT) is currently determined by its sparse baseline coverage. In particular, EHT coverage is dominated by long baselines, and is highly sensitive to atmospheric conditions and loss of sites between experiments. The limited short/mid-range baselines especially affect the imaging process, hindering the recovery of more extended features in the image. We present an algorithmic contingency for the absence of well-constrained short baselines in the imaging of compact sources, such as the supermassive black holes observed with the EHT. This technique enforces a specific second moment on the reconstructed image in the form of a size constraint, which corresponds to the curvature of the measured visibility function at zero baseline. The method enables the recovery of information lost in gaps of the baseline coverage on short baselines and enables corrections of any systematic amplitude offsets for the stations giving short-baseline measurements present in the observation. The regularization can use historical source size measurements to constrain the second moment of the reconstructed image to match the observed size. We additionally show that a characteristic size can be derived from available short-baseline measurements, extrapolated from other wavelengths, or estimated without complementary size constraints with parameter searches. We demonstrate the capabilities of this method for both static and movie reconstructions of variable sources.
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