First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass
First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass
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DOI：
10.3847/2041-8213/ac6736
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发表时间：
2022-05
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通讯作者：
Event Horizon Telescope Collaboration;K. Akiyama;A. Alberdi;W. Alef;J. Algaba;R. Anantua;K. Asada
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作者：
Event Horizon Telescope Collaboration;K. Akiyama;A. Alberdi;W. Alef;J. Algaba;R. Anantua;K. Asada
在本文中，我们量化了2017年4月EHT在1.3 mm波长处观察到的Sgr A* 的地平线尺度发射的时间变化和图像形态。我们发现Sgr A* 数据表现出的变化性超过了数据中的不确定性或星际散射的影响所能解释的。这种变化的幅度可以是相关通量密度的很大一部分，在某些基线上达到100%。通过简单的几何源模型的探索，我们证明了环状形态提供更好的适合Sgr A* 数据比其他形态具有可比的复杂性。我们开发了两种策略，用于拟合静态几何环模型的时间变量Sgr A* 数据;一种策略适合模型的短段数据的源是静态的，并平均这些独立的拟合，而另一个适合模型的完整的数据集使用参数模型的结构变异性功率谱周围的平均源结构。几何建模和图像域特征提取技术确定环直径为51.8 ± 2.3 μas（68%可信区间），环厚度限制为环直径的30%至50%之间的FWHM。为了使直径测量到一个共同的物理尺度，我们使用GRMHD模拟生成的合成数据对其进行校准。这种校准将引力半径的角大小限制为4.8 − 0.7 + 1.4 μas，我们联合收割机来自脉泽散射的独立距离测量，确定Sgr A* 的质量为4.0 − 0.6 + 1.1 × 10 6 M。
In this paper we quantify the temporal variability and image morphology of the horizon-scale emission from Sgr A*, as observed by the EHT in 2017 April at a wavelength of 1.3 mm. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching ∼100% on some baselines. Through an exploration of simple geometric source models, we demonstrate that ring-like morphologies provide better fits to the Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full data set using a parametric model for the structural variability power spectrum around the average source structure. Both geometric modeling and image-domain feature extraction techniques determine the ring diameter to be 51.8 ± 2.3 μas (68% credible intervals), with the ring thickness constrained to have an FWHM between ∼30% and 50% of the ring diameter. To bring the diameter measurements to a common physical scale, we calibrate them using synthetic data generated from GRMHD simulations. This calibration constrains the angular size of the gravitational radius to be 4.8 − 0.7 + 1.4 μas, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A* to be 4.0 − 0.6 + 1.1 × 10 6 M ⊙.