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γ射线暴是宇宙中恒星尺度的最剧烈爆发现象。γ射线暴瞬时辐射结束后,进入余辉辐射阶段。X射线耀发是γ射线暴X射线辐射衰减过程中出现的短时标闪耀现象。X射线耀发的脉冲轮廓具有不对称性,其上升时标小于下降时标。在部分γ射线暴中,X射线耀发的亮度达到瞬时辐射的亮度。X射线耀发的持续时间与峰值时间具有线性关系。X射线耀发的光谱比X射线余辉的光谱硬。早期X射线耀发与晚期X射线耀发相比,其脉冲轮廓较窄,光谱较硬。X射线耀发产生的物理过程类似于γ射线暴瞬时辐射的物理过程。在火球(fireball)模型中,内部壳层之间发生碰撞,产生的内激波加速电子,电子的同步辐射产生X射线耀发。当火球扫过星际介质,外激波加速电子时,电子的同步辐射也可产生X射线耀发。在光球(photospere)模型中,能量耗散发生在光学厚的区域,热辐射的光谱峰值落在X射线能段附近,γ射线暴的喷流在光球半径处会产生X射线耀发。如果射线暴喷流由坡印亭能流主导,喷流就会与星际介质相互作用,磁场的不稳定性使磁场发生耗散,产生的能量形成X射线耀发。γ射线暴的喷流具有几何效应。一部分同步辐射可能发生在喷流辐射面的高纬度处。由于曲率效应(curvature effect),各向异性辐射与各向同性辐射相比,X射线耀发的峰值出现较晚。此外,在γ射线暴发生后,黑洞会间歇性地吸积外部介质。在吸积过程中,黑洞周围的磁场会调节吸积的速率和喷流中的能量,这是出现多个X射线耀发的原因。 相似文献
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水超脉泽辐射( 各向同性光度超过 10 个太阳光度) 通常在星系中心最内部的核区( 小于几个秒差距) 被发现,因而活动星系核被认为是其唯一的能量源。同其它没有检测到水脉泽辐射的活动星系核相比,水脉泽寄主活动星系核可能隐含着某种或某些特殊性质。基于此我们调研了已经公开发表的所有水脉泽源的 X 射线观测情况,得到了一个有 X 射线观测研究结果的子样本( 39 个源) 。由它们的 X 射线光度以及估算的黑洞质量,导出了它们的无量纲吸积率( logL2-10keV /LEdd,其中 L2-10keV和 LEdd分别是 2 - 10keV 的固有光度和爱丁顿光度) ; 与距离范围相当的、没有检测到水脉泽的活动星系核样本相比,发现脉泽寄主活动星系核有较高的吸积率。进一步分析比较这两个活动星系核样本的质量吸积率,也发现类似的趋势。此外,为了探索吸积率和水脉泽辐射间可能的内在联系,我们对它们的脉泽光度和吸积率进行了统计分析,然而结果显示二者之间没有明显的相关性。 相似文献
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《天文研究与技术》2016,(1)
喷流的形成与黑洞吸积向来密不可分。分析黑洞吸积率与其喷流能量的相关性对研究黑洞内部结构以及喷流形成的具体原因具有重要的意义。从文献资料中收集了24个数据源,这些源包含了13个射电选BLLac天体(RBL)和11个平谱射电类星体(FSRQs)。通过样本数据研究黑洞吸积率与喷流能量以及γ射线流量密度的相关性。研究结果表明:(1)24个活动类星体的吸积率与喷流能量存在明显的相关性,这与Allen等得出的结论相同;(2)射电选BLLac天体与平谱射电类星体的喷流能量分布存在一定差异;(3)射电选BLLac天体的吸积率与γ射线流量密度相关性并不明显,但平谱射电类星体的吸积率与γ射线流量密度之间具有一定的相关性;(4)研究结果进一步证明了喷流能量不仅与黑洞质量有关,同时也很可能与黑洞的吸积存在关系。黑洞喷流的形成很可能是黑洞质量与吸积共同作用的结果。这些研究结果与其他方法获得的结果是一致的。 相似文献
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<正>活动星系核(AGN)、低光度活动星系核(LLAGN)以及X射线双星(XRB)系统中都存在黑洞吸积过程.黑洞吸积是人们理解相关天体的辐射、光变等现象的关键.本学位论文主要侧重于对目前非常流行的热吸积流(径移主导吸积流ADAF以及明亮热吸积流LHAF)的研究.该类吸积流是理解LLAGN以及处于硬态的XRB的基本理论模型.论文第1章详细介绍了相关的背景.首先讨论了天体环境中的黑洞及其所处的系统—AGN、 相似文献
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《天文研究与技术》2021,(4)
耀变体的喷流辐射机制是一个非常重要的问题。从文献中收集了442个耀变体的数据,这些耀变体包括215个平谱射电类星体(Flat Spectrum Radio Quasars, FSRQ)和227个蝎虎天体(BL Lac),通过数据研究了耀变体的喷流功率与多波段光度的相关性。研究结果表明:(1)对于平谱射电类星体,喷流功率与射电波段、光学波段、X射线和γ射线的光度都有强相关性,且光度分布顺序为logL_γ logL_O logL_X logL_R。(2)对于蝎虎天体,喷流功率与射电波段、光学波段和γ射线的光度都有强相关性,但是喷流功率与X射线的光度只有弱相关性;蝎虎天体的光度分布顺序为logL_O logL_γ logL_X logL_R,而且蝎虎天体的各波段光度都小于平谱射电类星体。我们认为这些差异是由于平谱射电类星体与蝎虎天体的内禀属性不同导致的,即吸积模式不同和喷流辐射机制不同等。 相似文献
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《天文学进展》2017,(4)
活动星系核是中央核区有剧烈活动的(河外)星系总称。随着观测技术不断进步,人们对活动星系核的研究越来越多,对其理解也越来越深刻。总结整理了近年来对活动星系核X射线本征谱指数与爱丁顿比关系的观测结果,揭示出如下V形关系图像:随着爱丁顿比由大变小,X射线本征谱指数与爱丁顿比由存在正相关关系,转变为存在负相关关系。一般认为,这一观测现象反映了随着吸积率的降低,黑洞吸积模式发生了变化,由高吸积率时的标准薄盘吸积变为低吸积率时的辐射无效吸积流。这表明,基于标准薄盘的最基本的活动星系核统一模型虽然能够成功地解释较高光度活动星系核的很多观测现象,但却需要做一定的修正,以解释低光度活动星系核的一些观测性质。同时,将来有希望利用这一相关关系估算活动星系核一些重要参数,如中央超大黑洞质量、吸积率等,从而帮助人们更好地理解活动星系核的辐射机制和演化过程。最后对这一领域的研究进行了总结与展望。 相似文献
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Ken Ebisawa Aya Kubota Tsunefumi Mizuno Piotr Życki 《Astrophysics and Space Science》2001,276(1):11-14
The Ultra-luminous Compact X-ray Sources (ULXs)in nearby spiral galaxies and the Galactic super-luminaljet sources sharethe common spectral characteristic that they haveextremely high disk temperatures which cannot be explainedin the framework of the standard accretion disk modelin the Schwarzschild metric. We have calculated an extreme Kerr disk model to examine if the Kerr disk model can instead explain the observed `too hot' accretion disk spectra.We found that the Kerr disk spectrum becomes significantly hardercompared to the Schwarzschild disk only when the disk is highlyinclined.For super-luminal jet sources, which are known to beinclined systems, the Kerr disk model may thuswork if we choose proper values for the black hole angular momentum. For the ULXs, however, the Kerr disk interpretation will be problematic,as is is highly unlikely that their accretion disks are preferentiallyinclined. 相似文献
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Most astrophysical accretion disks are likely to be warped.In X-ray binaries,the spin evolution of an accreting neutron star is critically dependent on the interaction between the neutron star magnetic field and the accretion disk.There have been extensive investigations on the accretion torque exerted by a coplanar disk that is magnetically threaded by the magnetic field lines from the neutron stars,but relevant works on warped/tilted accretion disks are still lacking.In this paper we develop a simplified twocomponent model,in which the disk is comprised of an inner coplanar part and an outer,tilted part.Based on standard assumption on the formation and evolution of the toroidal magnetic field component,we derive the dimensionless torque and show that a warped/titled disk is more likely to spin up the neutron star compared with a coplanar disk.We also discuss the possible influence of various initial parameters on the torque. 相似文献
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近年来对吸积流的数值模拟工作证实了在星风吸积中吸积盘的存在。本文在此基础上，讨论具有早型伴星的Ｘ射线脉冲星吸积过程中吸积盘与球吸积流的相互作用。我们发现，盘吸积率和球吸积率的相对变化可以导致吸积盘和吸积矩的改变，从而解释了这类脉冲星脉冲周期的复杂变化，我们以典型星ＶｅｌａＸ－１和Ａ０５３５＋２６为例分别作了讨论。 相似文献
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《天文和天体物理学研究(英文版)》2016,(4)
The peaks in the spectra of the accretion disks surrounding massive black holes in quasars are in the far-UV or soft X-ray band, which are usually not observed. However, in the disk corona model, soft photons from the disk are Comptonized to high energy in the hot corona, and the hard X-ray spectra(luminosity and spectral shape) contain information on the incident spectra from the disk. The values of black hole spin parameter a*are inferred from the spectral fitting, which are spread over a large range, ~-0.94 to 0.998. We find that the inclination angles and mass accretion rates are well determined by the spectral fitting, but the results are sensitive to the accuracy of black hole mass estimates. No tight constraints on the black hole spins are achieved, if the uncertainties in black hole mass measurements are a factor of four,which are typical for the single-epoch reverberation mapping method. Recently, the accuracy of black hole mass measurement has been significantly improved to 0.2- 0.4 dex with the velocity resolved reverberation mapping method. The black hole spin can be well constrained if the mass measurement accuracy is50%. In the accretion disk corona scenario, a fraction of power dissipated in the disk is transported into the corona, and therefore the accretion disk is thinner than a bare disk for the same mass accretion rate,because the radiation pressure in the disk is reduced. We find that the thin disk approximation, H/R0.1,is still valid if 0.3 m 0.5, provided half of the dissipated power is radiated in the corona above the disk. 相似文献
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The standard thin accretion disk model can explain the soft X-ray spectra of Galactic black hole systems and AGN successfully. However, there are still a few observational documents for Radiation pressure theory in X-ray novae in black hole binary systems and AGN. The luminosity in accretion onto black holes is corresponds to L>0.01L E . According to standard thin disk model, when the accretion rate is over a small fraction of the Eddington rate, L>0.01L E , the inner region of the disk is radiation-pressure-dominated and thermally unstable. However, observations of the high/soft state of black hole X-ray binaries with luminosity within (0.01L E <L<0.5L E ) show that the disk is quite stable. Thus, this contradiction shows the objection of this model and maybe it is essential to change the standard viscosity law or one of the other basic assumptions in order to get a stable disk models. In this paper, we revisit and recalculate the thermal instability with a different models of viscosity and cooling functions and show that the choosing of an arbitrary cooling and viscosity functions can affect on the stability of a general disk model and hence maybe answer to a this problem in accretion disk theory. We choose an arbitrary functions of surface density Σ and half thickness of disk H for cooling and viscosity. Also, we discuss a general disk with thermal conduction, radial force and advection. Then, we solve the equations numerically. We obtain a fourth degree dispersions relation and discuss solutions and instability modes. This analysis shows the great sensitivity of stability of disk to the form of viscosity, so there are various effective factors to stabilize the disk. For example the exist of advection and thermal conduction can effect to stability of disks also. 相似文献
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We show that the set of observational characteristics for low-mass X-ray binaries in the optical and X-ray bands can be explained
in terms of the model of an optically thick accretion disk with an atmosphere irradiated by a central X-ray source. We show
that this set of observational data can be successfully used to measure the orbital inclination of a binary, the geometric
parameters of its accretion disk, and the reprocessing time of X-emission to optical one. For the burster GS 1826-238, a low-mass
X-ray binary with a neutron star, we have estimated the binary inclination and the thickness of the disk atmosphere at the
outer edge from the mean optical flux and the amplitude of periodic modulations in the optical light curve: i = 62.5° ± 5.5° and H
d/R
d = 0.145 ± 0.009. The optical response time of the binary to an X-ray burst disagrees with the geometric delay in the propagation
of X-ray photons in the binary. We believe that this points to a finite X-ray reprocessing/reradiation time, 1.0 s ≲ τ
repr ≲ 2.2 s, in the hot atmosphere above the accretion disk. 相似文献
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Ye Lu K. S. Cheng National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Physics University of Hong Kong Hong Kong China 《中国天文和天体物理学报》2002,2(2):161-168
We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10^-6-10^-5M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs. 相似文献
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We briefly review recent developments in black hole accretion disk theory, emphasizing the vital role played by magnetohydrodynamic
(MHD) stresses in transporting angular momentum. The apparent universality of accretion-related outflow phenomena is a strong
indicator that large-scale MHD torques facilitate vertical transport of angular momentum. This leads to an enhanced overall
rate of angular momentum transport and allows accretion of matter to proceed at an interesting rate. Furthermore, we argue
that when vertical transport is important, the radial structure of the accretion disk is modified at small radii and this
affects the disk emission spectrum. We present a simple model demonstrating how energetic, magnetically-driven outflows modify
the emergent disk emission spectrum with respect to that predicted by standard accretion disk theory. A comparison of the
predicted spectra against observations of quasar spectral energy distributions suggests that mass accretion rates inferred
using the standard disk model may be severely underestimated. 相似文献
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We calculate the polarization of the radiation from an optically thick accretion disk with a vertical averaged magnetic field.
The polarization arises from the scattering of light by free electrons in a magnetized disk plasma. The Faraday rotation of
the polarization plane during the propagation of a photon in a medium with a magnetic field is considered as the main effect.
We discuss various models of optically thick accretion disks with a vertical averaged magnetic field. Our main goal is to
derive simple asymptotic formulas for the polarization of radiation in the case where the Faraday rotation angle Ψ ≫ 1 at
the Thomson optical depth τ = 1. The results of our calculations allow the magnetic field strength in the region of the marginally
stable orbit near a black hole to be estimated from polarimetric observations, including X-ray observations expected in the
future. Since the polarization spectrum of the radiation strongly depends on the accretion disk model, a realistic physical
model of the accretion disk can be determined from data on the polarization of its radiation. 相似文献
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《New Astronomy Reviews》2000,44(1-2):9-13
Our ability to study the hard X-ray emission in non-magnetic CVs has improved dramatically within the last decade. We review the important results on X-ray eclipses and dips, the current state-of-the-art in the modeling of X-ray spectra of CVs, then present some recent results on the hard X-ray emission from high accretion rate non-magnetic CVs. These results point to potential areas of conflict with accretion disk theories: the fate of the inner disk in quiescence, and the amount of material above the orbital plane. We conclude with some speculations on where near-future X-ray missions might take this field over the next decade. 相似文献