Using a combination of general-relativistic magnetohydrodynamics simulations and ray tracing of synchrotron emission, we study the effect of modest (24 degrees) misalignment between the black hole spin and plasma angular momentum, focusing on the variability of total flux, image centroids, and image sizes. We consider both millimeter and infrared (IR) observables motivated by Sagittarius A* (Sgr A*), though our results apply more generally to optically thin flows. For most quantities, tilted accretion is more variable, primarily due to a significantly hotter and denser "coronal" region well off the disk midplane. We find (1) a 150% increase in millimeter light curve variability when adding tilt to the flow; (2) the tilted image centroid in the millimeter shifts on a scale of 3.7 microarcseconds over 28 hours (5000 gravitational times) for some electron temperature models; (3) tilted disk image diameters in the millimeter can be 10% larger (52 versus 47 microarcseconds) than those of aligned disks at certain viewing angles; (4) the tilted models produce significant IR flux, similar to that seen in Sgr A*, with comparable or even greater variability than observed; (5) for some electron models, the tilted IR centroid moves by more than 50 microarcseconds over several hours, in a similar fashion to the centroid motion detected by the GRAVITY interferometer.
Wind-Fed GRMHD Simulations of Sagittarius A*: Tilt and Alignment of Jets and Accretion Discs, Electron Thermodynamics, and Multi-Scale Modeling of the Rotation Measure
The Intrinsic Shape of Sagittarius A* at 3.5-mm Wavelength
Sgr A $^\ast$的无线电发射被认为是由银河系中心一个超大质量黑洞$\sim\! 4\times10^6~ \rm{M}_\odot$的吸积提供动力的。在毫米波段，甚长基线干涉测量（VLBI）观测可以直接分辨出Sgr A $^\ast$最里面明亮的吸积区。由于在南北方向增加了许多敏感的长基线，我们在大型毫米波望远镜阿方索塞拉诺（LMT）上开发了一个完整的VLBI能力。我们用6台甚长基线望远镜阵和LMT组成的望远镜阵成功地探测到了3.5毫米的Sgr A $^\ast$。我们将源建模为椭圆高斯亮度分布，并从闭合振幅和自校准分析中估计源的散射大小和方向，获得方法和历元之间一致的结果。然后，我们使用已知的散射核来确定在3.5 mm处的固有二维源尺寸：$(147\pm7~μ\rm{as}) \times (120\pm12~μ\rm{as})$，在北偏东的位置角$88^\circ\pm7^\circ$处。最后，我们检测到一些基线三角形上的非零闭合相位，但我们表明，这些都是一致的被引入的折射散射在星际介质，并不需要内在的源不对称性来解释。
A Face-on Accretion Disk Geometry Revealed by Millimeter-wave Periodicity in Sgr A$^*$
School of Fundamental Science and Technology, Graduate School of Science and Technology, Keio University（庆应义塾大学理工学部理工学研究科基础科学与技术学院）；Department of Physics, Institute of Science and Technology, Keio University（庆应义塾大学理工学部理工学研究科物理学科）；Astronomical Science Program, Graduate Institute for Advanced Studies, SOKENDAI（SOKENDAI（日本国立天文台联合研究生院）天文学研究项目）；National Institute of Technology, Tokyo College（东京国立工业大学）
Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign
Universitat de València（瓦伦西亚大学）；University of Arizona（亚利桑那大学）；INAF-Istituto di Radioastronomia（意大利国家天体物理研究所射电天文台）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Observatori Astronòmic, Universitat de València（瓦伦西亚大学天文台）；Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo（圣保罗大学天文、地球物理和大气科学研究所）；Università degli Studi di Cagliari（卡利亚里大学）；INAF - Osservatorio Astronomico di Cagliari（意大利国家天体物理研究所卡利亚里天文台）；INFN, sezione di Cagliari（意大利国家核物理研究所卡利亚里分部）；Instituto de Astrofísica de Andalucía-CSIC（安达卢西亚天体物理学研究所）
