【作者】 黄昌印；

【导师】 汪定雄；

【作者基本信息】 华中科技大学 ， 理论物理， 2011， 博士

【摘要】 黑洞等致密天体的辐射通常呈现出快速的变化,有些x射线光变表现出持续稳定的近似周期性,被称为准周期振荡(QPO)。黑洞双星、中等质量黑洞和活动星系核(AGNs)都被观测到存在QPO。由于其时标与黑洞吸积盘内区的动力学时标相当,QPO被认为是探测黑洞附近吸积过程的有效途径。大尺度磁场在高能天体物理中扮演了重要角色,本文在大尺度磁场提能的基础上建立了黑洞双星的3：2高频QPO模型以及不同尺度黑洞系统的QPO统一模型,将QPO频率的产生与辐射谱联系起来。本轮共振模型自然地解释了3：2高频QPO的小整数比,但是能否克服吸积流的阻尼力对其来说是严重的困难。黑洞与吸积盘之间的磁耦合过程将旋转黑洞的能量和角动量转移到吸积盘内区,克服了共振团块在吸积流中遇到的阻尼力问题,并有利于建立QPO与谱态之间的联系。本文第二章将共振模型和黑洞与吸积盘之间的磁耦合过程结合起来,拟合了三个黑洞双星的3：2高频QPO以及对应的x射线谱形,表明3：2高频QPO是与陡幂律态成协的。黑洞双星、中等质量黑洞和AGNs在观测上表现出相似性和统一性,本文第三章尝试建立不同尺度黑洞系统的QPO统一模型。Kerr度规下黑洞吸积盘上的环向面电流分布会产生盘盘耦合的闭合大尺度磁场位形,我们考虑了磁耦合过程与盘冕系统的相互作用,利用盘上闭合磁力线的磁重联分别拟合了三种不同尺度黑洞系统的QPO以及对应的x射线谱形。黑洞双星的谱态转变呈现出纷繁复杂的现象,本文第四章试图用大尺度磁场位形的演化描述态转变,其中涉及到BZ、MC、BP三种大尺度磁场的提能机制。描述盘上磁场集中程度的幂律指数n起着关键作用,随着n的减小,BZ和BP过程的磁场先后消失,黑洞双星由低硬态过渡到硬中间态再转变到陡幂律态。我们拟合了这几个态的主要特征,并估计了由陡幂律态向热主导态转变的时标。描述黑洞双星态转变的HID图中的“喷流线”可以用a*和n参数空间中的临界线得到很好的说明。吸积盘上的发射线是探测盘内区的另一个有效途径,由于相对论效应,发射线被远处的观测者接收时变得很宽,铁Kα线最为明显。如果将QPO与铁Kα线结合起来,则有可能对吸积盘内区的特性作出更准确的判断。本文第五章利用大尺度磁场的磁耦合过程讨论了黑洞双星的3：2高频QPO与展宽的铁Kα线之间的可能关联。施加在吸积盘内边缘的外部力矩和非轴对称大尺度磁场的螺旋不稳定性分别在盘上产生内外热斑,双热斑的开普勒运动形成3：2 QPO。另一方面,由于内边缘力矩和大尺度磁场MC过程的作用,盘上的辐射很集中,随着半径的增加发射率衰减很快,由该发射率指数计算得到的铁Kα线展宽轮廓与观测值相吻合。更多还原

【Abstract】 Rapid variations are usually found in the radiation from black hole (BH) systems and other astrophysical compact objects. Some X-ray variations are quasi-periodic, stationary and continuing, which are called Quasi-Periodic Oscillations (QPOs). QPOs have been observed in BH binaries, intermediate mass BHs and active galactic nuclei (AGNs). QPO is believed to be an effective approach to detect the accretion process near BHs since its time scale is equivalent to the dynamical time scale in the inner region of an accretion disk. Large-scale magnetic fields play an important role in high energy astrophysics. In this thesis, a model for 3:2 high frequency QPO (HFQPO) pairs in BH binaries and a unified model for QPOs in BH systems of different scales are established, which link QPO frequencies and emitted spectra based on energy extraction via large-scale magnetic fields.The epicyclic resonance models interpret the small integer ratio of QPO frequency pairs naturally, but there remain serious uncertainties as to whether epicyclic resonance could overcome the severe damping forces in accretion flows. The severe damping can be overcome by transferring energy and angular momentum from a spinning BH to the inner disk via magnetic connection (MC) between the hole and the disk. And the MC process is helpful to understand the link between QPO frequencies and spectra. In Chapter 2, we combine epicyclic resonance and the MC process to fit the 3:2 HFQPO pairs and the corresponding spectra of three BH banaries. It turns out that the 3:2 HFQPO pairs are associated with the steep power-law (SPL) states.Observations show similarity and unity among BH binaries, intermediate mass BHs and AGNs. In Chapter 3, we attempt to establish a unified model for QPOs in BH systems of different scales. The toroidal electric currents distributed in accretion disk around a Kerr BH will generate closed large-scale magnetic fields connecting the inner and outer regions of accretion disk. We fit QPOs with the corresponding X-ray spectra in BH systems of different scales based on the MC effects on disk-corona system with magnetic reconnection of the closed field lines.Complicated phenomena have been observed in BH X-ray binaries. In Chapter 4, we attempt to describe the state transitions based on the evolution of large-scale magnetic fields and energy extraction invoking of the BZ, BP and MC processes. The power index n indicating the concentration of magnetic fields on the disk is a key parameter in state transitions. Magnetic fields with BZ and BP processes disappear successively with the decreasing n, and the low hard (LH) state transferred into hard intermediate (HIM) state, and then into SPL state. We fit the main characteristics of these states and the time scale of the transition from SPL state to thermal dominated (TD) state is roughly estimated. The ’jet line’in HID can be interpreted naturally by the critical line in a*-n parameter space.The relativistic X-ray emission line is another effective approach to detect the inner region of an accretion disk. The lines become very broad when received by distant observers due to the relativistic effects and Fe Ka lines are the most obvious. The characteristics of inner disk region may probably be understood better if we use the methods of QPOs and Fe Ka lines together. In Chaper 5, we discuss the probable connection between 3:2 HFQPOs and broad Fe Ka lines in two BH binaries based on the MC process.3:2 HFQPOs are generated by the Kepler motion of inner and outer hotspots in the disk which are produced by the external torque exerted at the inner edge of the disk and screw instability of non-axisymmetric large-scale magnetic field respectively. On the other hand, the radiation of the inner disk is very concentrative and the emissivity decreases rapidly with the increasing radius due to the torque exerted at the inner edge of the disk and the MC process. The curves of broad Fe Ka lines calculated from the steep emissivity index are in accordance with observations.更多还原