基于集合经验模态分解的类星体光变周期及其混沌特性分析

基于密歇根大学射电天文台数据库中从1965年到2012年收集的类星体3C 345,3C 273和3C 279在射电8.0 GHz的光变数据,利用集合经验模态分解方法将这些类星体的光变资料分解为周期项、趋势项和高频项,并对分解后的高频项计算其饱和关联维数、最大Lyapunov指数和Kolmogorov熵,判断是否具有混沌性.结果表明,这些类星体的光变不仅具有周期性,也具有明显的混沌特性,表明类星体光变应为产生周期性运动的物理机制和产生混沌现象的非线性机制的综合结果.     

The characteristic periodicity analysis of the radio flux variability of quasar PKS 1510-089

A wavelet analysis method is introduced to study the possible periods of PKS 1510-089 in radio bands. By compiling the radio light curve of PKS 1510-089 at frequencies of 22 and 37 GHz from 1990 to 2005, and using the wavelet analysis method, the evidence of quasi-periodic activity in PKS 1510-089 was obtained. The results indicate that: (1) There are two stable outburst periods of T1=(1.80±0.06) yr and T2= (0.90±0.07) yr presenting in the isoplethal map of PKS 1510-089 at the radio band 37 GHz; (2) there i...     

蝎虎天体OJ287中等时标光变的周期特性研究

收集了蝎虎天体OJ287光学B, V, R, I波段37年的观测数据, 获得了从1972年至2009年的光变曲线. 运用Lomb-Scargle傅里叶变换方法分析中等时标光变的周期性特性, 发现存在52.0±1.1 d与255±23 d的主要周期成分,并模拟了存在倍周期分岔的准周期信号, 与不同时段观测数据的相图和关联维数进行对比. 结果表明, OJ287具有多周期尺度特征, 不同时段准周期光变中谐波成分不同, 谐波成分的变化与次黑洞对主黑洞吸积流的扰动有关, 光变中的谐波成分可能是主黑洞吸积流受强扰动时分岔形成的.     

基于近似熵的斯隆数字化巡天中类星体光变复杂性分析

光变是类星体的重要观测特征之一,类星体在多个波段存在剧烈的光变现象.光变非常复杂,具有非线性特征.以斯隆数字化巡天(Sloan digital sky survey, SDSS) stripe 82天区中的类星体为研究对象,利用近似熵方法分析了类星体光变的复杂性.首先应用模拟信号检验了近似熵方法对周期序列、白噪声序列、混沌序列和组合序列的区分能力,验证了近似熵方法是一种识别不同类型时间序列的有效方法.再计算了SDSS第7次释放数据中光谱证认过的类星体光变的近似熵,并分析了它们的复杂性.结果表明:SDSS类星体光变的近似熵值最大值为0.58,类星体光变的复杂性介于周期序列和白噪声序列的复杂性之间,近一半样本的复杂性与混沌序列基本一致.     

美国“钱德拉”望远镜发现最遥远X射线流

天文学家从美国宇航局“钱德拉”X射线观测望远镜拍摄的类星体照片上 ,发现了最遥远的X射线流 ,从超巨黑洞到类星体中心延伸达 1 0万多光年的由高能粒子组成的这一射流 ,为天文学家提供了有关 1 2 0亿年前宇宙微波背景状态的信息。它能研究大爆炸后经过 1 4亿年的宇宙辐射 ,而此前最遥远的X射线流是在大爆炸后 30亿年左右。天文学家认为 ,类星体是拥有活跃中心超巨黑洞的星系 ,恒星与气体都被吸入这黑洞 ,这一吸入过程经常伴随有强烈高能粒子流的形成。当射线流中的电子以接近光速的速度离开类星体时 ,电子会穿透宇宙背景辐射“海洋” ,宇…     

基于结构函数方法的类星体证认

光变巡天是搜寻类星体的一个很有效的方法.应用归一化结构函数对SDSS stripe 82中存在光变的1411个类星体和174个恒星进行分类,选取幂函数模型拟合这些样本5个波段的结构函数.综合幅值和幂指数两个物理量设置了合适的分类判据,获得了比较理想的分类结果,类星体和恒星最高分类正确率分别达到了92.2%和83.6%.结果表明,改正后的结构函数对类星体的证认有很好的效果,能节约大型望远镜宝贵的观测时间,让类星体巡天获得比较高的观测效率.分析结论支持大部分类星体的光变缘于盘的不稳定性.     

Mkn 501 X射线和TeV射线准周期震荡的可能机制

我们提出了对流占主导的吸积流（ADAF）盘的辐射线是Mkn 501中从X射线到Tevγ射线的源光子；而且此盘的不稳定性可以解释Mkn 501中在X射线和Tevγ射线光变曲线23天的准周期光变。在这个模型中,光学到X射线辐射进入喷流，后由于喷流内相对论电子的作用而转化成高能光子。在这个过程中，发生在ADAF盘中的不稳定性导致源光子的准周期变化，从而导致了X射线和γ射线的变化。     

The parameters of binary black hole system in PKS 1510-089

Observations of PKS 1510-089 indicate the existence of a deep flux minimum with a timescale of \sim 35 min and an interval of about 336±14 d. A binary black hole system is proposed to be at the nucleus of this object. The secondary black hole orbits around the primary black hole. The minimum is caused by the periodic eclipse of the primary black hole by the secondary black hole. Based on the observations of PKS 1510-089, we estimate the parameters of the binary black hole system. The masses for the primary and secondary black holes are 1. 37×10⁹M_{\odot} (M_{\odot} is the solar mass) and 1. 37 \times 10⁷M_{\odot} , and the major axis for this pair being about 0.1 parsec(pc).     

类星体3C345的光变周期特性

收集了类星体3C345光学B波段100多年来较为完备的观测数据,获得了其长期光变曲线.利用小波分析的方法对其中B波段28年的数据进行了多时间尺度分析,并用小波变换系数图展示了3C345光学B波段的爆发过程.通过研究发现了其中存在有450天,780天,1830天和3540天的近似光变周期.利用小波逆变换可以反映其光变在不同时间尺度上的演变特征,进而预测类星体3C345未来可能的光学爆发时间为2010年左右. 关键词： 小波分析方法 光变曲线 多时间尺度 小波变换系数图     

大气压尖板电极结构重复频率纳秒脉冲放电中X射线辐射特性研究

文章通过碘化钠晶体和光电倍增管构成的X射线探测系统,研究了上升沿15ns,脉宽30-40ns量级,电压90kV的大气压重频纳秒脉冲气体放电中X射线的辐射特性,X射线有效探测能量范围为10-130keV.结果表明放电产生的X射线主要集中在20-90keV能量范围,而能量在十几keV的软X射线和超过90keV的高能X射线数量很少.X射线辐射计数随脉冲重复频率的增加而增加,随着气隙距离的改变存在峰值,且峰值出现在弥散放电模式.     

The variability of BL Lac 3C 66A

It is now known that there are supermassive black holes at the centre of a galaxy, surrounded by an accretion disc. The black hole-jet-accretion disc model plays an important role in the explanation of the observational properties of active galactic nuclei. BL Lacertae objects form a subclass of blazars; they are monitored through electromagnetic wave bands. During the OJ-94 project, 3C 66A was observed as a comparison object of OJ287 and found to display a possible 65-day period in the V light curve. In this paper, we show that the instability of an accretion disc surrounding a massive central black hole (2.5×10^{7}M_⊙) may explain this period in 3C 66A.     

Spin and mass of the supermassive black hole in the Galactic Center

A new method for exact determination of the masses and spins of black holes from the observations of quasi-periodic oscillations is discussed. The detected signal from the hot clumps in the accretion plasma must contain modulations with two characteristic frequencies: the frequency of rotation of the black hole event horizon and the frequency of the latitudinal precession of the clump’s orbit. Application of the method of two characteristic frequencies for interpretation of the observed quasi-periodic oscillations from the supermassive black hole in the Galactic center in the X-rays and in the near IR region yields the most exact, for the present, values of the mass and the spin (Kerr parameter) of the Sgr A* black hole: M = (4.2 ± 0.2) × 10⁶ M _⊙ and a = 0.65 ± 0.05. The observed quasi-periodic oscillations with a period of about 11.5 min are identified as the black hole event horizon rotation period and those with a period of about 19 min are identified as the latitudinal oscillation period of the hot spot orbits in the accretion disk.     

Synchrotron peak luminosity,black hole mass and Eddington ratio for SDSS flat-spectrum radio quasars

For a sample of 185 flat-spectrum radio quasars (FSRQs) constructed from the SDSS DR3 quasar catalog, we found a significant correlation between the synchrotron peak luminosity and both the black hole mass and Eddington ratio. This implies that the physics of its jet formation is not only tightly related with the black hole mass, but also with the accretion rate. We verify that the synchrotron peak luminosity can be a better indicator of jet emission than 5 GHz luminosity, through comparing the relationships between each of these two parameters and both black hole mass and Eddington ratio. The fundamental plane of black hole activity for our FSRQs is established as L _r ∝ L ^0.80±0.06_x M ^{−0.04±0.09}_bh with a weak dependence on black hole mass, however, the scatter is significant.

     

Redshift of a compact binary star in the neighborhood of a supermassive black hole

We present a method that allows to calculate the redshift of a compact binary star which moves in a strong external gravitational field, e.g. the field of a supermassive black hole. If the binary is close enough to the field center, its motion can be relativistic, while the relative motion of the stars in the binary is still non-relativistic. The latter can be computed in a co-moving reference frame. We calculate the redshift in a co-moving frame in Fermi coordinates as a series in the size of the binary \(\varrho \). The obtained expression is written in a covariant form up to linear terms in \(\varrho \). Using the equations of motion that have been obtained in a previous paper, we present the method of calculation of the redshift of a sample binary star moving in the field of a black hole. We illustrate this method by numerical model for the case of spherically-symmetric (Schwarzschild) black hole. The method can be applied to the analysis of the timing data of pulsars in the vicinity of the Galactic Center, and to the reconstruction of the binary star motion by its redshift.     

TeV activity of Cygnus X-3 high mass binary system

Cygnus X-3 is a high mass X-ray binary and microquasar, with a compact object, which is either a neutron star or may be a black hole, and a companion object, which is a Wolf-Rayet star. The nature of the compact object is still uncertain. Cygnus X-3 galactic binary system has been regularly observed since a 1995 by SHALON Atmospheric Cherenkov telescope with the average gamma-ray flux (6.8 ± 0.7) × 10⁻¹³ cm⁻² s⁻¹. The observations of very high-energy gamma-radiation from the sources of this type would be important for understanding the nature of this astrophysical object.     

Can Superconducting Cosmic Strings Piercing Seed Black Holes Generate Supermassive Black Holes in the Early Universe?

The discovery of a large number of supermassive black holes (SMBH) at redshifts , when the Universe was only 900 million years old, raises the question of how such massive compact objects could form in a cosmologically short time interval. Each of the standard scenarios proposed, involving rapid accretion of seed black holes or black hole mergers, faces severe theoretical difficulties in explaining the short‐time formation of supermassive objects. In this work we propose an alternative scenario for the formation of SMBH in the early Universe, in which energy transfer from superconducting cosmic strings piercing small seed black holes is the main physical process leading to rapid mass increase. As a toy model, the accretion rate of a seed black hole pierced by two antipodal strings carrying constant current is considered. Using an effective action approach, which phenomenologically incorporates a large class of superconducting string models, we estimate the minimum current required to form SMBH with masses of order by . This corresponds to the mass of the central black hole powering the quasar ULAS J112001.48+064124.3 and is taken as a test case scenario for early‐epoch SMBH formation. For GUT scale strings, the required fractional increase in the string energy density, due to the presence of the current, is of order 10⁻⁷, so that their existence remains consistent with current observational bounds on the string tension. In addition, we consider an “exotic” scenario, in which an SMBH is generated when a small seed black hole is pierced by a higher‐dimensional string, predicted by string theory. We find that both topological defect strings and fundamental strings are able to carry currents large enough to generate early‐epoch SMBH via our proposed mechanism.     

Central black hole masses of galaxies

In this paper, the stellar velocity dispersions in the host galaxies are used to estimate the central black hole masses for a sample of elliptical galaxies. We find that the central black hole masses are in the range of 10^{(5.5-9.5)}M_⊙. Based on the estimated masses in this paper and those by Woo & Urry (2002) and the measured host galaxy absolute magnitude, a relation, log (M_{BH}/M_⊙) = -(0.25±4.3×10^{-3})M_R + (2.98±0.208) is found for central black hole mass and the host galaxy magnitude. Some discussions are presented.