We present new calculations of X-ray polarization from accreting black holes (BHs), using a Monte-Carlo ray-tracing code in full general relativity. In our model, an optically thick disk in the BH equatorial plane produces thermal seed photons with polarization oriented parallel to the disk surface. These seed photons are then inverse-Compton scattered through a hot (but thermal) corona, producing a hard X-ray power-law spectrum. We consider three different models for the corona geometry: a wedge ``sandwich'' with aspect ratio H/R and vertically-integrated optical depth tau_0 constant throughout the disk; an inhomogeneous ``clumpy'' corona with a finite number of hot clouds distributed randomly above the disk within a wedge geometry; and a spherical corona of uniform density, centered on the BH and surrounded by a truncated thermal disk with inner radius R_edge. In all cases we find a characteristic transition from horizontal polarization at low energies to vertical polarization above the thermal peak; the vertical direction is defined as the projection of the BH spin axis on the plane of the sky. We show how the details of the spectropolarization signal can be used to distinguish between these models and infer various properties of the corona and BH. Although the bulk of this paper focuses on stellar-mass BHs, we also consider the effects of coronal scattering on the X-ray polarization signal from supermassive BHs in active galactic nuclei.
Diffuse neutrino flux from coronal magnetospheric current sheets of accreting black holes
National and Kapodistrian University of Athens（雅典国立卡波迪斯特里安大学）；Institute of Accelerating Systems and Applications（加速系统与应用研究所）；Columbia University（哥伦比亚大学）；Flatiron Institute（平顿研究所）
The upcoming IXPE (2-8 keV) and XL-Calibur (15-75 keV) missions will make it possible to measure the linear polarization of X-rays from mass accreting stellar mass black holes with unprecedented sensitivity, enabling the accurate measurement of percent-level and in some cases even sub-percent level polarization fractions. The measurements are expected to constrain the spins, inclinations, and the structure of the accretion flows of the observed black holes. The effects of Faraday rotation and birefringence of the Quantum Electrodynamics (QED) vacuum may impact the observable polarization fract…
The corona is a key component of most luminous accreting black holes, carrying 5 - 30 % of the power and in non-jetted Active Galactic Nuclei (AGN), creating all the X-ray emission above $\simeq 1-2$ keV. Its emission illuminates the inner accretion disc, creating the atomic line-rich reflection spectrum used to diagnose and map the accretion flow and measure black hole spin. The corona is likely powered magnetically by the strong differential rotation of the accretion disc and it may be intimately related to relativistic jets. Recent work shows that many black hole coronae may be dominated by…
The hard X-ray emission observed in accreting compact sources is believed to be produced by inverse Compton scattering of soft photons arising from the accretion disc by energetic electrons thermally distributed above the disc, the so-called X-ray corona. Many independent observations suggest that such coronae should be compact and located very close to the black hole. In this case general relativistic (GR) effects should play an important role to the continuum X-ray emission from these sources, and in particular in the observed high energy cut-off, which is a measure of the intrinsic temperat…
State transitions in black hole X-ray binaries are likely caused by gas evaporation from a thin accretion disk into a hot corona. We present a height-integrated version of this process which is suitable for analytical and numerical studies. With radius $r$ scaled to Schwarzschild units and coronal mass accretion rate $\dot{m}_c$ to Eddington units, the results of the model are independent of black hole mass. State transitions should thus be similar in X-ray binaries and AGN. The corona solution consists of two power-law segments separated at a break radius $r_b \sim10^3 \,(α/0.3)^{-2}$, where …
Fe K$α$ Profiles from Simulations of Accreting Black Holes
我们提出的第一个结果，从一个新的技术预测的Fe-K $α$配置文件直接从广义相对论磁流体动力学（GRMHD）模拟。从GRMHD模拟的数据处理的Monte Carlo全球辐射输运代码，它确定的X射线通量照射磁盘表面和日冕电子温度自洽。利用模拟得到的辐射通量和盘的密度结构，通过光电离平衡和辐射传输方程的求解，确定了再处理后的Fe K $α$发射。我们制作的地图的表面亮度的Fe K $α$排放的磁盘表面，其中-为我们的例子的$10 M_\odot$，史瓦西黑洞吸积在$1\%$爱丁顿值-急剧上升一个引力半径外的半径最内稳定的圆形轨道，然后下降$\propto r^{-2}$在更大的半径。我们解释这些功能的Fe K $α$径向表面亮度分布的磁盘的电离结构和扩展的日冕几何形状的后果，分别。我们还提出了相应的铁K $α$线的配置文件，将看到由遥远的观察者在几个倾角。我们预测的K $α$线的线轮廓和等效宽度的形状都与通常从吸积黑洞中观察到的线轮廓和等效宽度在定性上相似。最重要的是，这项工作代表了理论和观测之间的直接联系：在一个完全自洽的方式，我们产生可观察到的结果--铁荧光线轮廓--从黑洞吸积理论几乎没有唯象假设。
Radiation-dominated polar emitting region of an accreting X-ray pulsar -- I. Polarization- and spectrum-dependent structure, and the emergent continuum
Sternberg Astronomical Institute, Lomonosov Moscow State University（莫斯科国立大学列昂尼德·斯特恩伯格天体物理研究所）；Faculty of Physics, Lomonosov Moscow State University（莫斯科国立大学物理学院）
X-ray polarimetry can potentially constrain the unknown geometrical shape of AGN coronae. We present simulations of the X-ray polarization signal expected from AGN coronae, assuming three different geometries, namely slab, spherical and conical. We use the fully relativistic Monte-Carlo Comptonization code monk to compute the X-ray polarization degree and angle. We explore different coronal parameters such as shape, size, location and optical depth. Different coronal geometries give a significantly different X-ray polarization signal. A slab corona yields a high polarization degree, up to 14% …
Optical polarimetry of the accreting black hole X-ray binary Swift J1727.8$-$1613 over the state transition and radio ejections
University of Turku（图尔库大学）；Nordita, Stockholm University and KTH Royal Institute of Technology（北欧理论天体物理研究所，斯德哥尔摩大学和皇家理工学院）；Graduate School of Sciences, Tohoku University（东北大学研究院）；Istituto ricerche solari Aldo e Cele Daccó (IRSOL), Faculty of Informatics, Università della Svizzera italiana（瑞士意大利大学信息学院阿尔多和切莱达科太阳能研究所）
X-ray polarimetry missions like IXPE will be able to measure for the first time the polarization properties of accreting, weakly magnetized neutron stars in Low Mass X-ray Binaries. In this work we present simulations of the expected X-ray polarized signal including the coronal emission for different geometries of the corona itself, i.e. a slab above the accretion disc and a spherical shell around the neutron star. The simulations are performed with the fully relativistic Monte Carlo code monk capable of computing the X-ray polarization degree and angle for various physical input parameters of…
The origin of fast radio bursts (FRBs) remains mysterious. Recently, the only repeating FRB source, FRB 121102, was reported to possess an extremely large and variable rotation measure (RM). The inferred magnetic field strength in the burst environment is comparable to that in the vicinity of the super-massive black hole Sagittarius A* of our Galaxy. Here we show that all the observational properties of FRB 121102 (including the high RM and its evolution, the high linear polarization degree, an invariant polarization angle across each burst and other properties previously known) can be interpr…
Understanding the persistent emission is crucial for studying type I X-ray bursts, which provide insight into neutron star properties. Although accretion disc coronae appear to be common in many accreting systems, their fundamental properties remain insufficiently understood. Recent work suggests that Type I X-ray bursts from accreting neutron stars provide an opportunity to probe the characteristics of coronae. Several studies have observed hard X-ray shortages from the accretion disk during an X-ray burst implying strong coronal cooling by burst photons. Here, we use the plasma emission code…
Studies of the Origin of High-Frequency Quasi-Periodic Oscillations of Mass Accreting Black Holes in X-ray Binaries with Next-Generation X-ray Telescopes
The physical properties of the accretion flow and of the X-ray emitting plasma, in supermassive black holes accreting at extreme Eddington rates, are still very unclear. Here we present the analysis of simultaneous XMM-Newton and NuSTAR observations of the hyper-Eddington Seyfert 1 galaxy IRAS 04416+1215, carried out in 2020. The main goal of these observations is to investigate the properties of the X-ray corona, as well as the structure of the accretion flow and of the circumnuclear environment, in this regime of extreme accretion. IRAS 04416+1215 has one of the highest Eddington ratio ($λ_{…
Inelastic scattering effects on polarization predictions for cold and warm atmospheres in the X-rays
Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）；INAF Istituto di Astrofisica e Planetologia Spaziali（意大利国家天体物理与行星物理学研究所(INAF)）；Dipartimento di Fisica e Astronomia, Università degli Studi di Padova（帕多瓦大学物理与天文系）；Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550（斯特拉斯堡大学、法国国家科学研究中心、斯特拉斯堡天文台）；Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre（罗马第三大学数学与物理系）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文中心）；Nordita, KTH Royal Institute of Technology and Stockholm University（北欧理论天体物理中心(Nordita)、瑞典皇家理工学院和斯德哥尔摩大学）
Department of Physics, McLennan Physical Labs, Toronto, ON M5S 1A7, Canada（多伦多大学物理系）；Canadian Institute for Theoretical Astrophysics, 60 St. George St., Toronto, ON M5S 3H8, Canada（加拿大理论天体物理研究所）
We describe upgrades to a numerical code which computes synchrotron and inverse-Compton emission from relativistic plasma including full polarization. The introduced upgrades concern scattering kernel which is now capable of scattering the polarized and unpolarized photons on non-thermal population of electrons. We describe the scheme to approach this problem and we test the numerical code against known analytic solution. Finally, using the upgraded code, we predict polarization of light that is scattered off sub-relativistic thermal or relativistic thermal and non-thermal free electrons. The …
What's the Buzz About GX 13+1? Constraining Coronal Geometry with QUEEN-BEE: A Bayesian Nested Sampling Framework for X-ray Polarization Rotation Analysis
本文提出贝叶斯嵌套采样框架 QUEEN-BEE，用于分析 IXPE 数据中 GX 13+1 的 X 射线偏振旋转，首次约束其冕几何为片状，并展示其在低信噪比下识别演化偏振特征的能力。
Cen X-3 is the first X-ray pulsar discovered 50 years ago. Radiation from such objects is expected to be highly polarized due to birefringence of plasma and vacuum associated with propagation of photons in presence of the strong magnetic field. Here we present results of the observations of Cen X-3 performed with the Imaging X-ray Polarimetry Explorer. The source exhibited significant flux variability and was observed in two states different by a factor of ~20 in flux. In the low-luminosity state no significant polarization was found either in pulse phase-averaged (with the 3$σ$ upper limit of…
The Event Horizon Telescope (EHT) has recently released high-resolution images of accretion flows onto two supermassive black holes. Our physical understanding of these images depends on accuracy and precision of numerical models of plasma and radiation around compact objects. The goal of this work is to speed up radiative-transfer simulations used to create mock images of black holes for comparison with the EHT observations. A ray-tracing code for general relativistic and fully polarized radiative transfer through plasma in strong gravity is ported onto a graphics processing unit (GPU). We de…
We discuss the possibility that accreting black hole systems can be sources for dark matter flux through several different mechanisms. We firstly discuss two types of systems: coronal thermal plasmas around supermassive black holes in active galactic nuclei (AGNs), and accretion disks of stellar-mass X-ray black hole binaries (BHBs). We explore how these black hole systems may produce keV light dark matter fluxes and find that the dark fluxes from those sources might be too weak to account for the current XENON1T excess. On the other hand, black holes can be good accelerators to accrete and bo…
Broadband Timing and Spectral Study of Accreting Millisecond X-ray Pulsar SAX J1808.4$-$3658 during Its 2022 Outburst
Inter-University Centre for Astronomy and Astrophysics (IUCAA)（大学间天文学与天体物理学中心）；Universitá degli Studi di Cagliari（卡利亚里大学）；Department of Applied Sciences, UPES（印度石油大学应用科学系）
High-sensitivity X-ray polarimetric observations of black hole X-ray binaries, which will soon become available with the launches of space-borne X-ray observatories with sensitive X-ray polarimeters, will be able to put independent constraints on the black hole as well as the accretion flow, and possibly break degeneracies that cannot be resolved by spectral/timing observations alone. In this work we perform a series of general relativistic Monte-Carlo radiative transfer simulations to study the expected polarization properties of X-ray radiation emerging from lamp-post coronae in black hole X…
