黑洞候选体X射线双星Cyg X-1光变曲线的研究

利用Rossi X-ray Timing Explorer(RXTE)卫星从1996年1月到2005年5月的公共资料,研究了黑洞候选体X射线双星Cyg X-1光变曲线的周期性,并且发现了一些有趣的周期特性(T=1．0±0．2天和T=18．0±3．0天)．在硬态时,T=1．0±0．2天和T=18．0±3．0天的周期特性同时出现在它的光变曲线之中,但在软态时仅有T=1．0±0．2天的周期出现．采用一种新的方法(即微分法),同时为了检验微分法的正确性,还利用传统的方法(即快速傅立叶变换和叠加法)分析了相同的资料,并得到了与微分法相同的结果．另外也对Cyg X-1的轨道周期进行了研究,结果发现T=5．6天的轨道周期不仅出现在硬态,同时也出现在软态,只是在硬态时比在软态时明显．     

The additional radiation of Cyg X-1 at primary minimum

New UBV-photoelectric observations of the well-known massive X-ray binary system Cyg X-1/V 1357 Cyg are obtained near the primary minimum. The detailed analysis of these observations confirms the existence of additional blue radiation which appears as a narrow peak with an amplitude of 0.01–0.02 mag near phase 0.00 on the light curve (the superior conjunction of the relativistic component), firstly detected by Lyuty (1985). This emission does not appear at every orbital cycle. The appearance of this narrow peak of additional blue radiation on the light curve of Cyg X-1 can be explained as the radiation of relativistic electrons in the disturbed magnetic field of the optical star in frames of the model proposed by Ikhsanov and Fabrika (1990).     

A Study on the Periodicity of Hardness Ratio of the X-ray Binary Cyg X-1 as a Black Hole Candidate

Using the All-Sky Monitor (ASM, 1.5∼12 keV) data of Rossi X-ray Timing Explorer (RXTE) from January 1996 to October 2011, we have analyzed in detail the power spectrum of the hardness ratio (HR) (5∼12 keV/3∼5 keV) of the X-ray binary Cyg X-1 as a black hole candidate. The results show that the HR exhibits the following periodical variations: (1) During MJD = 50087∼55841, the HR presented the the periods T ≈ 5.6 d, T ≈ 40.0 d, T ≈ 78.4 d, T ≈ 173.8 d, and T ≈ 400/800 d; (2) When Cyg X-1 was in the hard state, the HR exhibited the periods T ≈ 5.6 d, T ≈ 33.7/67.6 d, T ≈ 45.3 d, and T ≈ 165.3 d; (3) When Cyg X-1 was in the soft state, the HR exhibited the periods T ≈ 38.5 d, T ≈ d, and T ≈ 128.3 d. Moreover, using the viscosity theory and Zdziarski accretion disk model, we have made a discussion on the physical mechanism of this kind of periodicity.     

CygX-1 X辐射的功率谱

运用自回归功率谱研究CygX－1X辐射的频谱特征,结果显示CygX－1转换态和高／软态时变频谱的连续成分,可以统一由有截断的幂律加噪声成分描述,转换态存在小于3Hz的宽峰结构及准周期振荡（QPO）成分（4－12Hz）,而高／软态完全可由截断幂律谱描述,不存在显著的QPO．截断频率在各态都相当稳定,在不同态的演化与平流为主的吸积流模型（ADAF）预期的情形一致．本文结果表明,自回归功率港分析是研究X射线双星光变特征的一个有效的方法．     

The short timescale bursts of Cyg X-1 in the high and transitional states

Short timescale bursts or “shots” of Cyg X-1 in one ms time bins were obtained from PCA/RXTE observation. By superposing many shots lined up at the peak, a mean profile was obtained, and this was done seperately for the different states, high, transitional and low. The mean shot profile is different for the different states. The duration of shot is shorter in the high than in the transitional state. In both, the duration is about 0.11 s, which is shorter than in the low state. The profile is more asymmetrical in high than in low energy bands. In the transitional state, the average hardness during shots is lower than that of the steady component. The mechanism of shot generation is discussed.     

Cyg X-1高态中短暴性质的研究

CygX-1高能辐射的时变特征可以通过短暴(shot)的性质反映．因此CygX-1的短暴性质，特别是处于低态时的性质曾被广泛研究,利用直接叠加短暴和自相关函数，对CygX-1高态时短暴的性质进行了研究．结果表明，当CygX-1处于高态时，其短暴的结构类似于低态时所具有的性质，短暴的半高宽随能量的增加按指数下降．此结果和康普顿化模型不一致．另外，短暴的能谱演化及结构的非对称性可以解释CygX-1中的时延现象．     

Observation of ultra low hard X-ray flux from Cyg X-1 —A possible partial occulation of the X-ray source

The black hole candidate Cyg X-1 was observed in ultra low state on march 30, 1997 using Large Area Scintillation counter Experiment (LASE) in the hard X-ray energy region of 20–180 keV. During the 30 minute exposure a combined signal of 68 sigma was obtained, however, the measured flux at 50 keV was lower by a factor of 2 than the minimum flux reported so far. Using the recent orbital ephemeris of the source, our snap-shot observations were made at ϕ_5.6 = 0.915, which corresponds to the binary minimum revealed by the ASM light curves. The daily average data from the BATSE detectors give the source intensity level to be higher by a factor of 5. Very low flux values measured in the present experiment suggest that the hard X-ray source may have been partially occulted by the primary companion during its transit near the X-ray minimum.     

Results of Light Curve Analysis of the Massive Binary Cyg X-1/V1357 Cyg in Primary Minimum

The results of new UBV photometric observations of V1357 Cyg in primary minimum are presented. Observations were carried out from 1996 up to now with 60 cm telescope in Crimea with the goal to study additional radiation that was detected in the mean light curve of this system near orbital phase 0.0. The properties of this additional radiation are also considered.     

基于Jurkevich法CygX-1光变周期特性研究

针对天文观测数据不等间隔的特点,利用Jurkevich方法对黑洞候选体x射线双星CygX-1近16年的RossiX-rayTimingExplorer（RXTE）All-SkyMonitor（ASM）数据进行了频谱分析,并结合Kidger周期存在可信度的判据,发现CygX-1存在363±11．5d的光变周期,但没有发现420d的光变周期,而且150d的光变周期可能仅仅是51±1．4d光变周期的观测表象。     

Frequency-resolved spectroscopy of Cyg X-1: fast variability of the reflected emission in the soft state

Using RXTE /PCA data, we study the fast variability of the reflected emission in the soft spectral state of Cyg X-1 by means of Fourier frequency-resolved spectroscopy. We find that the rms amplitude of variations of the reflected emission has the same frequency dependence as the primary radiation down to time-scales of ≲30–50 ms. This might indicate that the reflected flux reproduces, with nearly flat response, variations of the primary emission. Such behaviour differs notably from that of the hard spectral state, in which variations of the reflected flux are significantly suppressed in comparison with the primary emission, on time-scales shorter than ∼0.5–1 s.
If related to the finite light-crossing time of the reflector, these results suggest that the characteristic size of the reflector, presumably an optically thick accretion disc, in the hard spectral state is larger by a factor of ≳5–10 than in the soft spectral state. Modelling the transfer function of the disc, we estimate the inner radius of the accretion disc to be R _in∼100 R _g in the hard state and R _in≲10 R _g in the soft state for a 10-M_⊙ black hole.     

Spectral measurements of Cyg X-3: A thermal source embedded in hot plasma within a cold shell

The attempts at unified model fitting to explain the spectral variations in Cyg X-3 suggest equally probable fits with a combination of an absorbed blackbody and a separately absorbed power law with an exponential cut-off or a composite of absorbed free-free emission with a power law hard X-ray component apart from the iron emission line. These seemingly ordinary but ad hoc mixtures of simple X-ray emission mechanisms have a profound implication about the geometry of the X-ray source. While the first set suggests a black-hole nature of the compact object, the second combination is consistent with a neutron star binary picture. The spectral variability at hard X-ray energies above 30 keV can provide crucial input for the unified picture. In this paper, we present spectral observations of Cyg X-3, made in our on-going survey of galactic and extragalactic X-ray sources in the 20–200 keV energy region, using Large Area Scintillation counter Experiment. The data show a clear power-law photon spectrum of the form dN/dE ∼ E^−2.8 in the 20 to 130 keV energy range. A comparison with earlier data suggests that the total number of X-ray photons in the entire 2–500 keV energy band is conserved at all time for a given luminosity level irrespective of the state. We propose that this behaviour can be explained by a simple geometry in which a thermal X-ray source is embedded in a hot plasma formed by winds from the accretion disk within a cold shell. The high/soft and low/hard X-ray states of the source are simply the manifestation of the extent of the surrounding scattering medium in which the seed photons are Comptonized and hot plasma can be maintained by either the X-ray driven winds or the magneto-centrifugal winds.     

Cyg X-1频谱的细微结构

利用线性状态空间模型（Ｌｉｎｅａｒ Ｓｔａｔｅ Ｓｐａｃｅ Ｍｏｄｅｌ－ＬＳＳＭ）,将 Ｃｙｇ Ｘ－１的功率谱分解为ＬＳＳＭ产生的模型功率谱和剩余功率谱两部分．集中分析剩余功率谱,结果显示, Ｃｙｇ Ｘ－１在低／硬态、转换态和高／软态三种状态的剩余功率谱有着不同的结构特征．其中高／软态和低／硬态的剩余功率谱存在一个宽峰结构,中心频率分别为～ ８ Ｈｚ和～ ５ Ｈｚ,低／硬态的剩余功率诺在～ ０．０７ Ｈｚ达到极大;转换态的剩余功率谱有双峰结构,其中心频率分别在～０．５—４Ｈｚ和～５—１１Ｈｚ,与我们以前分析的 ＱＰＯ的中心频率很接近,说明 ＱＰＯ与线性状态空间所要求的自回归模型可能属于不同的物理过程．与总功率谱比较,剩余功率谱对谱的变化部分（例如ＱＰＯ、截断频率等）更为敏感,本文对剩余功率谱中谱峰变化的原因做了初步的探讨．     

The time lag of high-energy photons of Cyg X-1 in hard state

The time lag between hard and soft X-rays is an important aspect of the study of high-energy emission. Fourier cross spectrum, often used in calculating the time lag, is unable to measure statistically significant fast light variation above Fourier frequency 30 Hz from the measurements of Cyg X-1. The method of cross correlation function in time domain, developed by Li Ti-pei, can be effectively used in measuring time lags on different time scales. Using Li's method we discuss the properties of the time lag of high-energy photons of Cyg X-1 in hard state at different times. The results show that there is a significant time lap on short times scales (< 0.1 s). We confront different models of hard-state Cygnus X-1 with the observed time lag.     

Cyg X-1高态和转换态的X射线短时标爆发

分析ＲＸＴＥ卫星ＰＣＡ探测器对ＣｙｇＸ－１的观测数据,得到了其处于高态及高低态转换时的Ｘ射线短时标爆发（Ｓｈｏｔ）结构．在所观测到的三种态中是不对称的,并且不同的状态中Ｓｈｏｔ的结构有明显差异．Ｓｈｏｔ前后沿可分别由双指数函数近似拟合．Ｓｈｏｔ中的快时变过程是由慢的上升前沿和快的下降后沿构成．在所观测态中Ｓｈｏｔ平均宽度约为０．１１秒（ＦＷＨＭ）,比低态时的宽度窄．同一状态中高能段的Ｓｈｏｔ宽度较低能段窄,且更加不对称．转换态的硬度在Ｓｈｏｔ峰前有明显下降,之后迅速上升,Ｓｈｏｔ期间的平均硬度低于非Ｓｈｏｔ期平均值;而高态时峰前硬度没有明显下降,Ｓｈｏｔ期间的平均硬度高于非Ｓｈｏｔ期间的平均值．本文还就Ｓｈｏｔ的产生机制进行了讨论．     

A complete relativistic ionized accretion disc in Cygnus X-1

The galactic black hole candidate Cygnus X-1 is observed to be in one of two X-ray spectral states: either the low/hard (low soft X-ray flux and a flat power-law tail) or high/soft (high blackbody-like soft X-ray flux and a steep power-law tail) state. The physical origin of these two states is unclear. We present here a model of an ionized accretion disc, the spectrum of which is blurred by relativistic effects, and fit it to the ASCA , Ginga and EXOSAT data of Cygnus X-1 in both spectral states. We confirm that relativistic blurring provides a much better fit to the low/hard state data and, contrary to some previous results, find the data of both states to be consistent with an ionized thin accretion disc with a reflected fraction of unity extending to the innermost stable circular orbit around the black hole. Our model is an alternative to those that, in the low/hard state, require the accretion disc to be truncated at a few tens of Schwarzschild radii, within which there is a Thomson-thin, hot accretion flow. We suggest a mechanism that may cause the changes in spectral state.     

The X-ray spectrum of Cyg X-2

The spectra of disc accreting neutron stars generally show complex curvature, and individual components from the disc, boundary layer and neutron star surface cannot be uniquely identified. Here we show that much of the confusion over the spectral form derives from inadequate approximations for Comptonization and for the iron line. There is an intrinsic low-energy cut-off in Comptonized spectra at the seed photon energy. It is very important to model this correctly in neutron star systems as these have expected seed photon temperatures (from either the neutron star surface, inner disc or self-absorbed cyclotron) of ≈1 keV, clearly within the observed X-ray energy band. There is also reflected continuum emission which must accompany the observed iron line, which distorts the higher energy spectrum. We illustrate these points by a reanalysis of the Ginga spectra of Cyg X-2 at all points along its Z track, and show that the spectrum can be well fitted by models in which the low-energy spectrum is dominated by the disc, while the higher energy spectrum is dominated by Comptonized emission from the boundary layer, together with its reflected spectrum from a relativistically smeared, ionized disc.     

The orbital period of HDE 226868/Cyg X-1

We present epoch 1996, high-quality radial velocity data for HDE 226868, the optical counterpart of Cygnus X-1. Combining our results with all published historical data, we have derived a new ephemeris for the system of HJD 245 0235.29 + n  × 5.5998, which allows accurate orbital phase calculations to be made for any X-ray observations over the last 30 years. We find no evidence for any period change such as that suggested by Ninkov, Walker &38; Yang. We discuss the shortcomings of previous work in establishing the period and orbital elements.