The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA
The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA
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DOI：
10.3847/1538-4357/aaf732
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发表时间：
2019-01
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通讯作者：
S. Issaoun;S. Issaoun;Michael D. Johnson;L. Blackburn;C. Brinkerink;M. Mościbrodzka;A. Chael;C. Go
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作者：
S. Issaoun;S. Issaoun;Michael D. Johnson;L. Blackburn;C. Brinkerink;M. Mościbrodzka;A. Chael;C. Go
银河系中心超大质量黑洞人马座A* (Sgr A*)是利用甚长基线干涉测量（VLBI）直接成像技术研究黑洞吸积和流出动力学的最有希望的目标之一。在3.5 mm （86 GHz）波段，Sgr A*的发射可以用全球毫米波VLBI阵列（GMVA）分辨。我们首次利用阿塔卡马大型毫米/亚毫米阵列（ALMA）加入GMVA，对Sgr A*进行观测。我们的观察结果达到了~ 87 μas的角分辨率，比以前的实验提高了两倍。我们重建了Sgr a *在3.5 mm处的未散射源结构的第一张图像，减轻了星际散射的影响。非散射光源的长轴尺寸为120±34 μas（12±3.4 Schwarzschild半径），具有对称的形状（轴比为），并且在3σ范围内具有与零一致的闭合相。我们表明，Sgr A*的多个圆盘主导模型符合我们的观测约束，而考虑的两个射流主导模型受到小视角的约束。我们对ALMA的长基线探测也为Sgr A*的散射提供了新的约束条件，我们表明，对于Sgr A* 1.3 mm的图像，事件视界望远镜的折射散射效应可能很弱。我们的研究结果为Sgr A*的固有形态和折射散射提供了迄今为止最严格的约束，证明了ALMA对毫米VLBI的特殊贡献。
The Galactic center supermassive black hole Sagittarius A* (Sgr A*) is one of the most promising targets to study the dynamics of black hole accretion and outflow via direct imaging with very long baseline interferometry (VLBI). At 3.5 mm (86 GHz), the emission from Sgr A* is resolvable with the Global Millimeter VLBI Array (GMVA). We present the first observations of Sgr A* with the phased Atacama Large Millimeter/submillimeter Array (ALMA) joining the GMVA. Our observations achieve an angular resolution of ∼87 μas, improving upon previous experiments by a factor of two. We reconstruct a first image of the unscattered source structure of Sgr A* at 3.5 mm, mitigating the effects of interstellar scattering. The unscattered source has a major-axis size of 120 ± 34 μas (12 ± 3.4 Schwarzschild radii) and a symmetrical morphology (axial ratio of ), which is further supported by closure phases consistent with zero within 3σ. We show that multiple disk-dominated models of Sgr A* match our observational constraints, while the two jet-dominated models considered are constrained to small viewing angles. Our long-baseline detections to ALMA also provide new constraints on the scattering of Sgr A*, and we show that refractive scattering effects are likely to be weak for images of Sgr A* at 1.3 mm with the Event Horizon Telescope. Our results provide the most stringent constraints to date for the intrinsic morphology and refractive scattering of Sgr A*, demonstrating the exceptional contribution of ALMA to millimeter VLBI.