HIGH-RESOLUTION LINEAR POLARIMETRIC IMAGING FOR THE EVENT HORIZON TELESCOPE
HIGH-RESOLUTION LINEAR POLARIMETRIC IMAGING FOR THE EVENT HORIZON TELESCOPE
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DOI：
10.3847/0004-637x/829/1/11
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发表时间：
2016-09-20
影响因子：
4.9
通讯作者：
Bouman, Katherine L.
中科院分区：
文献类型：
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作者：
Chael, Andrew A.;Johnson, Michael D.;Bouman, Katherine L.
活动星系核（AGN）周围同步辐射的线性偏振图像突出了它们的投影磁场线，并为理解超大质量黑洞的吸积和流出物理学提供了关键数据。活动星系核的最高分辨率偏振图像是由甚长基线干涉测量（VLBI）产生的。由于VLBI对源图像的傅里叶变换不完全采样，因此任何填充未测量空间频率的图像重建都不是唯一的，并且需要重建算法。在本文中，我们探讨了最大熵方法（MEM）的线性极化VLBI成像的一些扩展。与以前的工作相比，我们的偏振MEM算法结合了斯托克斯我的成像仪，只使用双谱测量是免疫大气相位腐败，与联合斯托克斯Q和U成像仪，操作强大的偏振比。我们证明了我们的技术的有效性7和3毫米波长的类星体观测VLBA和模拟1.3毫米事件视界望远镜观测的Sgr A* 和M87。与过去的研究一致，我们发现，极化MEM可以产生上级分辨率相比，标准的CLEAN算法，成像时平滑和紧凑的源分布。作为成像框架，MEM具有高度适应性，允许对偏振结构进行一系列约束。因此，偏振MEM是一个有吸引力的选择与EHT的图像重建。
Images of the linear polarizations of synchrotron radiation around active galactic nuclei (AGNs) highlight their projected magnetic field lines and provide key data for understanding the physics of accretion and outflow from supermassive black holes. The highest-resolution polarimetric images of AGNs are produced with Very Long Baseline Interferometry (VLBI). Because VLBI incompletely samples the Fourier transform of the source image, any image reconstruction that fills in unmeasured spatial frequencies will not be unique and reconstruction algorithms are required. In this paper, we explore some extensions of the Maximum Entropy Method (MEM) to linear polarimetric VLBI imaging. In contrast to previous work, our polarimetric MEM algorithm combines a Stokes I imager that only uses bispectrum measurements that are immune to atmospheric phase corruption, with a joint Stokes Q and U imager that operates on robust polarimetric ratios. We demonstrate the effectiveness of our technique on 7 and 3 mm wavelength quasar observations from the VLBA and simulated 1.3 mm Event Horizon Telescope observations of Sgr A* and M87. Consistent with past studies, we find that polarimetric MEM can produce superior resolution compared to the standard CLEAN algorithm, when imaging smooth and compact source distributions. As an imaging framework, MEM is highly adaptable, allowing a range of constraints on polarization structure. Polarimetric MEM is thus an attractive choice for image reconstruction with the EHT.