A wealth of Galactic accreting X-ray binaries have been observed both in low/hard state and high/soft state. The transition between these two states was often detected. Observation shows that the transition luminosity between these two states is different for different sources, ranging from 1% to 4% of the Eddington luminosity. Even for the same source the transition luminosity at different outbursts is also different. The transition can occur from 0.0069 to 0.15 Eddington luminosity. To investigate the underlying physics, we study the influence of viscosity parameter $α$ on the transition luminosity on the basis of the disk-corona model for black holes. We calculate the mass evaporation rate for a wide range of viscosity parameter, $0.1\le α\le 0.9$. By fitting the numerical results, we obtain fitting formulae for both the transition accretion rate and the corresponding radius as a function of $α$. We find that the transition luminosity is very sensitive to the value of $α$, $L/L_{\rm Edd}\proptoα^{2.34}$. For $0.1\leα\le 0.6$, the transition luminosity varies by two orders of magnitude, from 0.001 to 0.2 Eddington luminosity. Comparing with observations we find that the transition luminosity can be fitted by adjusting the value of $α$, and the model determined values of $α$ are mostly in the range of observationally inferred value. Meanwhile we investigate the truncation of the disk in the low/hard state for some luminous sources. Our results are roughly in agreement with the observations.
Insight-HXMT, NuSTAR and INTEGRAL Data Show Disk Truncation in the Hard State of the Black-Hole X-Ray Binary MAXI J1820+070
我们研究了吸积中的黑洞双星MAXI J1820+070的硬态X射线和软γ射线谱。我们对HXMT、NuSTAR和INTEGRAL的联合光谱进行了分析。我们发现所有三颗卫星的光谱之间存在总体一致性。令人满意的适合的数据需要大量的光谱复杂性，我们的模型包括两个康普顿化区域和相关的磁盘反射，磁盘黑体和窄Fe K $α$线。我们的拟合证实了至少在$>$ 10引力半径处存在反射光学厚盘的截断。然而，我们发现，HXMT数据本身不能显着约束磁盘内半径。
Beyond Disk Truncation: X-ray Reverberation Signatures of an Outflowing Corona
School of Physics and Technology, Wuhan University（武汉大学物理科学与技术学院）；Newcastle University（纽卡斯尔大学）；Universitat Politècnica de Catalunya（加泰罗尼亚理工大学）；Institut d’Estudis Espacials de Catalunya（加泰罗尼亚空间研究所）
Evidence for Disk Truncation at Low Accretion States of the Black Hole Binary MAXI J1820+070 Observed by NuSTAR and XMM-Newton
我们目前的结果从NuSTAR和XMM-牛顿观测新的黑洞X射线双星MAXI J1820+070在低吸积率（低于1%的爱丁顿光度）。我们检测到一个狭窄的铁K $α$发射线，在相反的广泛和不对称的铁K $α$线配置文件通常存在于黑洞二进制在高吸积率。具有弱相对论性增宽的窄线表明Fe K $α$线是在大圆盘半径处产生的。与假设标准盘发射率的盘反射模型拟合发现一个大的盘截断半径（几十到几百个引力半径，取决于盘的倾斜度）。此外，我们检测到准周期振荡（QPO）的频率之间变化的$11.6\pm0.2$ ~mHz和$2.8\pm0.1$ ~mHz。根据Lense-Thirring进动模型，非常低的QPO频率表明光学薄康普顿化区域的尺寸很大，支持吸积盘从ISCO后退，并在低吸积速率下被平流主导的吸积流所取代。我们还讨论了另一种吸积几何的可能性，即窄的Fe K $α$线是由一个灯柱电晕与一个大的高度照亮磁盘。
Systematic assessment of disk truncation in the black hole X-ray binary Swift J1727.8-1613 using NICER
Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内库克天文学研究所）；Department of Physics, Villanova University（维拉诺瓦大学物理系）；Dr. Karl Remeis-Observatory and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg（弗里德里希-亚历山大埃尔朗根-纽伦堡大学卡尔·雷梅斯天文台与埃尔朗根高能粒子物理中心）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）；Department of Physics, Stanford University（斯坦福大学物理系）；Kavli Institute for Particle Astrophysics and Cosmology, Stanford University（斯坦福大学卡弗里粒子天体物理学与宇宙学研究所）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；School of Mathematics, Statistics and Physics, Newcastle University（纽卡斯尔大学数学、统计与物理学院）
Outflow Behavior from the Transonic Advective Disks: A Hydrodynamical Simulation Study
Aryabhatta Research Institute of Observational Sciences（阿亚巴塔观测科学研究所）；Department of Applied Physics, Mahatma Jyotiba Phule Rohilkhand University（马哈特马·乔蒂巴·普尔罗希勒坎德大学应用物理系）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）
Studies of Thermally Unstable Accretion Disks around Black Holes with Adaptive Pseudospectral Domain Decomposition Method. II. Limit-Cycle Behavior in accretion disks around Kerr black holes
Challenging the disk instability model: I -- The case of YZ LMi
YZ LMi的观测表明，在爆发期间以及当静止盘较大时，沿流轨迹的发射增强，超出了盘边缘的影响。我们研究了这些功能是否可以解释在任何气流溢出或渗透的框架内的磁盘不稳定性（DIM）和传质不稳定性（MTIM）模型的爆发盘。气流溢出是不可能的，因为气流的垂直刻度高度显著低于外盘，并且因为没有参数组合能够在较大的盘上实现气流溢出，同时防止其在较小的盘上发生。气流穿透要求气流密度大于外盘区域。低粘度DIM盘不能满足这一要求，因为在发生热粘性不稳定性的整个传质速率范围内，其密度显著大于气流的密度。另一方面，高粘度MTIM盘具有低得多的密度，其随着半径的增加而减小，容易在爆发期间（当传质速率和流密度增加时）以及在大的静止盘中允许气流渗透。观察到的特征与DIM不一致，但可以用MTIM解释。这些结果表明，YZ LMi的爆发是高粘度盘对增强的传质速率爆发的响应。在这种情况下，（2-3）d的爆发下降时标意味着α =3-4范围内的粘度参数。
Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Contribution to AGN disk viscosity
State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）；School of Astronomy and Space Sciences, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；National Astronomical Observatory of China（中国科学院国家天文台）
Disk truncation triggers relativistic jet launching of a highly accreting supermassive black hole
Tohoku University（东北大学）；Nagoya City University（名古屋市立大学）；National Astronomical Observatory of Japan（日本国立天文台）；University of Miyazaki（宫崎大学）；The University of Osaka（大阪大学）；Shibaura Institute of Technology（芝浦工业大学）；National Institute of Technology, Ichinoseki College（国立工学期仙学院）
MRI Turbulence versus $α$-Viscosity in Circumbinary Disks: Implications for Gravitational-Wave Dephasing and Accretion Variability
Center for Cosmology and Particle Physics, Physics Department, New York University（纽约大学物理系宇宙学与粒子物理中心）；Center for Computational Astrophysics, Flatiron Institute（西蒙斯平顿研究所计算天体物理学中心）
