发表机构
Black Hole Initiative at Harvard University; Wake Forest University; Northwestern University; Institute for Advanced Study（哈佛大学黑洞倡议; 维克森林大学; 西北大学; 高等研究院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用Sgr A*的多仪器光变曲线数据，通过解析预测、透镜化模拟和GRMHD模拟三种框架分析其结构函数，发现MAD模型更符合观测，尤其在5-15分钟尺度上。
AI 中文摘要
在目前能够实现事件视界尺度成像的两个黑洞中，M87$^\ast$和Sgr A$^\ast$，只有我们银河系中心的Sgr A$^\ast$表现出亚小时尺度的光变，这使得对内部吸积流的光变曲线观测对于时空及周围等离子体的时域研究尤为宝贵。观测到的光变曲线通常以可变的采样间隔进行采样，因此常使用结构函数来量化其光变特性。在本工作中，我们汇集了一个由$\sim12$年内在230 GHz频率下通过不同仪器、不同持续时间和不同采样间隔获得的离散观测组成的Sgr A$^\ast$光变曲线异质数据集，并在三个框架下研究其结构函数。首先，我们考虑具有由Matérn协方差决定的傅里叶谱的平稳随机过程的结构函数特征的解析预测。然后，我们研究了在空间和时间上均用Matérn协方差近似的合成光学薄吸积流的透镜化影片所产生的结构函数，并识别出结构函数中哪些特征可归因于黑洞几何。最后，我们检查了由72个广义相对论磁流体动力学模拟组成的库的结构函数。我们发现，总体而言，磁 arrested 盘（MAD）模型产生的结构函数比标准及正常演化（SANE）模型更平滑，且斜率更陡。在5-15分钟的时间尺度上，观测到的Sgr A$^\ast$结构函数斜率更接近MAD趋势，而两种模拟类型在所有亚小时时间尺度上通常都比数据更具变异性。
英文摘要
Of the two black holes, M87$^\ast$ and Sgr A$^\ast$, for which event-horizon-scale imaging is currently achievable, only Sgr A$^\ast$ at our Galactic Center exhibits sub-hour variability, making light curve observations of the inner accretion flow especially valuable for time-domain studies of the spacetime and the surrounding plasma. Observed light curves are often sampled with variable cadence, so a structure function is often used to quantify their variability properties. In this work, we assemble a heterogeneous Sgr A$^\ast$ light curve data set from discrete observations acquired over $\sim12$ years {at 230 GHz}, with different instruments, durations, and cadences, and study its structure function in three frameworks. First, we consider analytic predictions for the features of structure functions of stationary random processes with Fourier spectra dictated by the Matérn covariance. We then study the structure functions resulting from lensed movies of synthetic optically thin accretion flows approximated with Matérn covariance in both space and time, and identify which features in the structure function can be attributed to the black-hole geometry. Lastly, we examine the structure functions of a library of $72$ general relativistic magnetohydrodynamic simulations. We find that, in general, magnetically arrested disk (MAD) models produce smoother structure functions with steeper slopes than standard and normal evolution (SANE) counterparts. On time scales of $5-15$ minutes, the observed structure function slope of Sgr A$^\ast$ more closely aligns with the MAD trend, while both simulation types are generally more variable than the data on all sub-hour timescales.
Comments10 pages, 5 figures, accepted in ApJL
