Accretion disks around stellar-mass black holes (BHs) emit radiation peaking in the soft X-rays when the source is in the thermal state. The emerging photons are polarized and, for symmetry reasons, the polarization integrated over the source is expected to be either parallel or perpendicular to the (projected) disk symmetry axis, because of electron scattering in the disk. However, due to General Relativity effects photon polarization vectors will rotate with respect to their original orientation, by an amount depending on both the BH spin and the observer's inclination. Hence, X-ray polarization measurements may provide important information about strong gravity effects around these sources. Along with the spectral and polarization properties of radiation which reaches directly the observer once emitted from the disk, in this paper we also include the contribution of returning radiation, i.e. photons that are bent by the strong BH gravity to return again on the disk, where they scatter until eventually escaping to infinity. A comparison between our results and those obtained in previous works by different authors show an overall good agreement, despite the use of different code architectures. We finally consider the effects of absorption in the disk material by including more realistic albedo profiles for the disk surface. Our findings in this respect show that considering also the ionization state of the disk may deeply modify the behavior of polarization observables.
Modeling X-ray reflection spectra from disk returning radiation: Application to 4U 1630-47
Eberhard-Karls Universität Tübingen（蒂宾根大学）；Fudan University（复旦大学）；Ulugh Beg Astronomical Institute of the Uzbekistan Academy of Sciences（乌兹别克斯坦科学院乌卢格别克天文研究所）；New Uzbekistan University（新乌兹别克斯坦大学）；University of Warwick（华威大学）
X-ray Reflection and An Exceptionally Long Thermonuclear Helium Burst from IGR J17062-6143
来自吸积中子星的热核X射线爆发对周围环境的短暂但强烈的辐射，为研究吸积物理提供了一种独特的方法。我们分析了2015年IGR J17062-6143观测到的一天闪光的MAXI/GSC和Swift/XRT光谱。这是一个罕见的在0.15%爱丁顿低吸积光度下重复爆发的例子。从2015年爆发和2012年前一次爆发之间拍摄的MAXI，Chandra和NuSTAR观测的光谱被用来确定吸积柱。我们发现它与5x10^10 g cm^-2的爆发点火柱一致，这表明它很可能是由在深氦层中燃烧提供动力的。观测到的爆发通量超过一天，并按照直接的幂律衰减：F~t^-1.15。爆发和持久的光谱很好地描述了从中子星的热辐射，康普顿化的这种发射在一个热的光学薄介质周围的恒星，和光电离的吸积盘的反射。在爆发峰值处，康普顿化分量消失，此时爆发可以耗散康普顿化气体，并且它在爆发尾部返回。反射信号表明，内盘在爆发前被截断在约100个引力半径处，但在爆发期间可能会向恒星靠近。在爆发结束时，通量下降到低于爆发冷却趋势2天，然后返回到爆发前水平。
The bright black hole X-ray binary 4U 1543-47 during 2021 outburst. A clear state transition from super-Eddington to sub-Eddington accretion revealed by Insight-HXMT
From reflection to scattering: Polarimetric signatures of funnel-type outflows. Modeling obscured ultraluminous X-ray sources
University of Turku（图尔库大学）；KTH Royal Institute of Technology and Stockholm University（瑞典皇家理工学院和斯德哥尔摩大学）；Nordita（北欧理论天体物理学研究所）；Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Space Research Institute (IKI)（空间研究所（IKI））；University of Oxford（牛津大学）
The First X-ray Polarimetry of GRS 1739--278 Reveals Its Rapidly Spinning Black Hole
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）；University of Chinese Academy of Sciences（中国科学院大学）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）；Department of Astronomy, University of Geneva（日内瓦大学天文系）；Fluid and Complex Systems Centre, Coventry University（考文垂大学流体与复杂系统中心）；INAF—Istituto di Astrofisica e Planetologia Spaziali（意大利国家天体物理研究所空间天体物理学和行星科学研究所）；Department of Physics and Astronomy, University of Southampton（南安普顿大学物理与天文系）；Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre（罗马第三大学数学与物理系）；NASA Marshall Space Flight Center（美国国家航空航天局马歇尔太空飞行中心）
