Low-Luminosity Accretion in Black Hole X-Ray Binaries and Active Galactic Nuclei

At luminosities below a few percent of Eddington, accreting black holes switch to a hard spectral state which is very different from the soft blackbody-like spectral state that is found at higher luminosities. The hard state is well-described by a two-temperature, optically thin, geometrically thick, advection-dominated accretion flow (ADAF) in which the ions are extremely hot (up to 10¹² K near the black hole), the electrons are also hot (∼10^9−10.5 K), and thermal Comptonization dominates the X-ray emission. The radiative efficiency of an ADAF decreases rapidly with decreasing mass accretion rate, becoming extremely low when a source reaches quiescence. ADAFs are expected to have strong outflows, which may explain why relativistic jets are often inferred from the radio emission of these sources. It has been suggested that most of the X-ray emission also comes from a jet, but this is less well established.     

The Formation of Black Hole Binaries

A peak exists in the distribution of observed black hole masses and no satisfactory explanation has been forthcoming so far. Here, we attempt an interpretation. We first establish a link between the helium core mass and the initial black hole mass, based on the result of 2-dimensional simulation of stellar core collapse by Fryer et al. Then the helium core masses are computed by using the PPE stellar evolution code, and the distribution of initial black hole masses for black hole binaries in stellar populations II and I is obtained. These are then compared with observations.     

A Fundamental Plane of Black Hole Activity: Pushing Forward the Unification Scheme

We examine the disc-jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the hard X-ray and radio bands. We compile a sample of ∼100 active galactic nuclei with measured mass, 5 GHz core emission, and 2–10 keV luminosity, together with eight galactic black holes with a total of ∼50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L_R) and the X-ray (L_X) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and L_X, at a highly significant level. We show how this result can be used to extend the standard unification by orientation scheme to encompass unification by mass and accretion rate.     

GRS 1915+105的X射线能谱分析及黑洞自旋测量

GRS 1915+105是银河系内的低质量黑洞X射线双星,其能谱和黑洞自旋已经得到了广泛的研究.自2018年6月开始,其X射线流量下降到了低流量水平,其间偶尔会产生多波段的耀发.利用Insight-HXMT(Insight-Hard X-ray Modulation Telescope,简称为慧眼)卫星在2020年8月30日到2020年10月13日之间对GRS1915+105的观测数据,研究了其能谱特性,发现在此次爆发过程中, X射线能谱可以用一个康普顿化的多温黑体谱很好地拟合.整个爆发的硬度强度图(Hardness-Intensity Diagram, HID)一直处于软态.采用GRS1915+105的最新动力学参数M=12.4_-1.8^+2.0M⊙, i=60°±5°, D=8.6_-1.6^+2.0kpc (M、M⊙、i和D分别表示黑洞质量、太阳质量、盘倾角和距离),得到其无量纲黑洞自旋a*的一个下限a*> 0.9990,确认了GRS 1915+105是一个具有极端自旋的黑洞.考虑本地吸收体的...     

黑洞吸积盘的演化及温度分布的热不稳定性

本文在Ｔｈｏｒｎｅ工作的基础上讨论了吸积盘中黑洞的有关参量的演化，以及由Ｓｃｈｗａｒｚｓｃｈｉｌｄ黑洞吸积盘向Ｋｅｒｒ黑洞吸积盘演化过程中对吸积盘辐射通量的影响，最后针对几个典型的辐射过程，分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性，并给出此类问题的热不稳定性的判据。     

The Evolution of Massive Close Binaries

We present results of evolutionary computations for massive close binaries with the Brussels simultaneous evolution code for conservative and non-conservative Roche lobe overflow (RLOF). We discuss mass transfer in massive close binaries during phases of RLOF, common envelope, spiral-in and merging. We examine the effects of stellar wind during successive stellar evolution phases and the final fate of primaries. We show how our library can be used to explain well-known binaries such as the WR + OB system V444 Cyg, HMXBs Vela X-1 and Wray 977, LMXBs like Her X-1, and binary pulsars. More details on the evolution of massive close binaries can be found in “The Brightest Binaries” (Vanbeveren et al., 1998).     

Evolution of The Spin Periods of Neutron Stars in Low Mass X-ray Binaries

We present a numerical analysis of the spin evolution of neutron stars in low-mass X-ray binaries, trying to explain the discrepancy in the spin period distribution between observations of millisecond pulsars and theoretical results. In our calculations, we take account of possible effects of radiation pressure and irradiation-induced instability on the structure of the disk, and the evolution of the mass transfer rate, respectively. We report the following results: (1) The radiation pressure in the accretion disk leads to a slight increase of spin periods, and the variation of mass transfer rate caused by the neutron star irradiation can shorten the spin-down phase of evolution. (2) The calculated results of the model combining radiation pressure and irradiation show that the accretion is strongly limited by the radiation pressure in the high mass transfer phase. (3) The accreted mass and fastness parameter can affect the number of systems in the equilibrium state.     

恒星级黑洞的观测证认研究进展

具有不同质量的恒星在耗尽其热核能源后,最终可能会坍缩成为性质完全不同的致密天体,如白矮星、中子星或者黑洞。从20世纪30年代起,黑洞的观测及其证认一直是天体物理学的研究热点之一。首先简要地回顾了恒星级黑洞的形成及其候选天体的研究历史;然后介绍了如何从观测上证认恒星级黑洞:接着详细讨论了恒星级黑洞的质量和自转参数的测量方法;最后介绍恒星级黑洞观测及其证认的最新研究进展,并做出结论:目前已经有充分的证据宣告在部分吸积X射线双星中存在恒星级黑洞。     

The Density and Masses of Obscured Black Holes

Recent Chandra and XMM-Newton surveys have uncovered a large fraction of the obscured AGN responsible of the hard X-ray background. One of the most intriguing results of extensive programs of follow-up observations concerns the optical and near-infrared properties of the hard X-ray sources counterparts. More specifically, for a significant fraction of hard X-ray obscured sources the AGN responsible of the high X-ray luminosity remains elusive over a wide range of wavelengths from soft X-rays to near-infrared. This very observational result opens the possibility to investigate the host of bright obscured quasars in some detail. Here we briefly report on some preliminar results obtained for a small sample of elusive AGN in the HELLAS2XMM survey.     

Comparing Black Hole and Neutron Star Variability

There are remarkable similarities between the rapid X-ray variability of low-magnetic field neutron stars in low mass X-ray binaries, and that of black holes. In particular at frequencies < 100 Hz, their power spectra can be strikingly similar. The highest frequency phenomena (kilohertz QPOs, black hole high-frequency QPOs and neutron star hectohertz QPOs) are the ones that show most differences, perhaps because they originate closest to the compact object. Most variability components vary in frequency in correlation with one another, and the correlations once again are very similar across neutron stars and black holes – some extend even to white dwarfs. Although this does not strictly require that all phenomena whose frequencies are involved are caused by the same physics in all three source types, this does indicate that basic properties of the accretion flow which are the same in all three source types play an important role in generating at least some of the frequencies.     

黑洞双星的B型QPO频率与幂律通量的相关性的解释

观测表明, 黑洞双星的B型准周期振荡(Quasi-Periodic Oscillation, QPO)频率与幂律通量之间存在正相关性. 试图基于阿尔文波振荡模型定量解释该相关性. 标准薄吸积盘辐射通量极大值处的阿尔文波振荡产生QPO. 标准薄盘上的软光子与冕或喷流基部的热电子介质发生逆康普顿散射产生幂律通量. 通过吸积率的连续变化, 得到QPO频率与幂律通量关系的分析解和数值解. 模拟得到的相关性在合理的参数范围内与观测值相吻合. QPO频率与幂律通量的正相关性可以理解为, 较强的磁场导致较高的阿尔文波频率和较高的电子温度从而得到较高的幂律通量. 结果表明B型QPO可能与吸积盘或喷流中的环向磁场的活动有关.     

双黑洞系统的不同起源及其参数分布

双黑洞组成的近密双星系统并合是激光干涉仪引力波天文台等地基引力波探测器的主要探测对象。随着探测器灵敏度的提高,大量该类信号的探测将成为进一步研究黑洞物理的有效工具。但是目前对双黑洞系统的起源机制和内禀参数分布等物理问题的研究还不够深入,例如由引力波探测得到的黑洞质量分布与X射线双星观测的结果存在较大差异,还未有很好的理论模型可解释该结果。目前普遍认为双黑洞系统主要有两种起源:大质量双星演化机制和动力学起源机制。基于这两类起源的双黑洞系统在质量、自旋分布等方面存在差异。因此可在贝叶斯理论框架下,利用引力波信号携带的波源质量和自旋等信息,推断波源起源,计算不同起源的双黑洞系统所占比例,以及检验质量自旋等参数分布的差异。     

EGUP与黑洞熵的修正值

目前,人们对黑洞Bekenstein-Hawking熵的量子修正值产生了极大的兴趣,尤其是黑洞熵对数修正项的系数.在广义不确定关系(GUP)的基础上,通过引入了推广的广义不确定关系(EGUP),运用面积定理计算了3类时空的黑洞熵的修正值,得到的黑洞熵的修正项的系数是正的.这种计算方法不仅对单视界时空适用,而且对有内视界的黑洞时空依然成立,并且在EGUP基础上计算出黑洞熵的修正值.相比GUP基础上得到的黑洞熵,EGUP可以应用于大尺度时空下,所以应用范围更广.此计算方法简洁明了,物理意义明确,可为黑洞熵对数修正值系数的确定提供参考.     

The Masses of Black Holes in X-ray Binary Systems

Recent results concerning the determination of the masses of eleven black hole candidates in X-ray binary systems are summarized. It is very significant that there are no pulsars or X-ray bursters of the first kind among the eleven known massive (mx > 3M) X-ray sources in close binary systems.     

激变双星的角动量损失机制和演化

本文详细研究了激变双星系统的演化，发现磁制动机制导致的角动量损失要求星风的量级为１０￣（－１１）－１０￣（－１２）Ｍ＿⊙ｙｒ￣－１，这比太阳风强１０￣２－１０￣３倍，表明磁星风机制失效，作者认为驱动双星系统演化的角动量损失是由来自致密星的吸积盘外边缘物质溢出的惯性离心力所致。     

TeV Gamma Rays From the Galactic Center Direct and Indirect Links to the Massive Black Hole in Sgr A

The recent detection of TeV gamma-radiation from the direction of the Galactic Center within several arc-minutes around Sgr A^* is the first model-independent evidence of existence of high-energy particle accelerator(s) in the central 10 pc region of our Galaxy. This is an extraordinary site that harbours many remarkable objects with the compact radio source Sgr A^* – a hypothetical super-massive black hole (SMBH) – in the dynamical center of the Galaxy. Here we explore the possible direct and indirect links of the reported TeV emission to the SMBH. We show that at least three γ-ray production scenarios that take place close to the event horizon of the SMBH can explain the reported TeV fluxes. An alternative (or additional) channel of TeV radiation is related to the run-away protons accelerated in Sgr A^*. Quasi-continuous injection of relativistic protons into the surrounding dense gas environment initiates detectable high-energy gamma-ray emission. The absolute flux and the energy spectrum of this radiation component strongly depend on the history of particle injection and the character of diffusion of protons during the last 10⁵ yr. For a reasonable combination of a few model parameters, one can explain the detected gamma-ray flux solely by this diffuse component.     

On the Correlation between Radio Properties and Black Hole Mass of Quasars

The question whether the radio properties of quasars are related to the mass of the central black hole or the accretion rate is important for our understanding of the formation of relativistic jets, but no consensus has been reached from statistical analyses. Using two large quasar samples, one radio-selected, one optical-selected, we re-exarnined these relations and find that previous differences between radio- and optical- selected samples can be ascribed, at least partly, to the effect of the narrow line component. All previous claimed correlations are much weaker, if exist at all.     

光学相机FOC对黑洞双星高时间分辨测光性能研究

黑洞暂现双星MAXI J1820+070于2018年3月的明亮爆发为研究光学快速测光能力提供了重要机遇. 以快速光学相机(Fast Optical Camera, FOC)为终端设备分别在2018年4月22日、5月26日和8月31日(UTC)使用云南天文台丽江观测站2.4m望远镜对爆发中的黑洞双星MAXI J1820+070进行了亚秒时标的测光观测. 通过观测数据分析, 研究了相机的快速测光性能.对全帧和1/4帧两种观测模式的帧间间隔(frame time), 测得平均帧间间隔为(22.866 pm 0.679)ms和(5.868 pm 0.169)ms. 通过视场中多颗明亮参考源校准,提取了观测对象和参考源的光变曲线, 获得了光变曲线的傅里叶功率谱, 区分了观测对象本征光变和仪器或望远镜等观测因素带来的非本征光变, 成功探测到目标黑洞双星MAXI J1820+070中的光学波段低频准周期振荡信号, 并判别了观测中来自仪器设备或与观测条件相关的时变信号. 这成功验证了相机高速稳定的测光性能和对短至5ms时标光变信号的探测能力.