Circinus X-1 在转换期的能谱和功率谱

Circinus X-1是小质量X射线双星(LMXB),它的能谱和时变十分复杂而独特。在不同的观测时期,它的硬度强度图(HID)和双色图(CCD)显示了不同的形状。本文选择了Circinus X-1正处于X射线流量从高向低转换期间的观测数据,通过对这一时期HID和相应能谱和时变性质的讨论,并将所得结果与1997年观测到的高亮度期间的能谱和时变性质(Shirey 1999)进行对比研究,进一步找到源的强度变化对其X射线辐射性质的影响。     

BATSEγ射线暴和太阳硬X射线暴的强度和时间特征

本文研究了CGRO卫星上BATSE探测器对硬X天空监测过程中触发和记录到的1 0 0 0多个γ暴和 40 0 0多个太阳硬X射线暴的强度和时间性质 ,发现它们的强度分布相似 ,这也许意味着硬X射线天空中两种主要的爆发现象机制相似 ,同时对将γ暴的强度分布作为其宇宙学起源的证据提出了疑问 .对太阳暴的持续时间分析表明 ,其强度和持续时间呈正相关 ,而γ暴是弱负相关 .太阳暴的强度和持续时间在BATSE运行过程中有长时标变化 ,最近对γ暴的研究也发现了这种现象     

磁星的观测特性和理论模型

磁星(magnetar)是一类有着极强磁场的致密天体,它们的外部磁场强度是典型中子星磁场强度的100～1 000倍。在过去几十年中,软γ射线复现源(SGR)和反常X射线脉冲星(AXP)被认为是最有可能的磁星候选者。磁星有着独特的能谱性质和光变特征,它的观测现象丰富多彩,其观测波段跨越了射电、红外、光学、X射线和γ射线等。近些年来,多种理论模型也相继被提出来,以解释其独特的性质。以正常脉冲星为例,介绍了磁星与通常中子星的不同性质,详述了磁星在多波段的能谱、光变及周期跃变现象等观测特性,总结了为解释磁星的特殊性质而建立起来的多种理论模型,并详述了中子星框架下的扭曲磁层模型。此外还介绍了其他候选模型。     

太阳脉冲式硬X射线爆发的谱分析理论

本文对脉冲式硬X射线暴的X辐射谱提出新的理论分析方法。指出电子数密度能态函数必须遵循基本动力学方程。在一些典型的源函数情形下,求得了电子数密度的能谱解。它们可以用来作为脉冲式硬X射线暴X辐射谱分析的基础。文中也对这些能态函数作了初步讨论,有助于说明X辐射谱的软化现象。     

宇宙信息

十年来发现的首个新软γ射线再现源 2008年8月22日美国宇航局的雨燕γ射线暴探测器探测到了来自一颗强磁星爆发所产生的X射线,仅仅12个小时之后,欧洲空间局的牛顿X射线多镜面望远镜就对准了这一目标,开始对它进行详细地分光观测。     

γ射线暴的时变分析

γ射线暴是天空中突然的硬X射线/γ射线爆发现象,有着非常复杂的光变曲线。由于光变现象和辐射过程直接相关,因此,研究γ射线暴的时变规律是非常重要的。对γ射线暴的一些时变现象以及通过时变研究得出的分类、脉冲形状、功率谱、时间演化、光度等性质进行了总结,并对一些结果进行了讨论。     

X和γ天文谱线观测结果的可靠性

各种现行被采用的估计太阳和宇宙X及γ谱线观测结果显著性的方法都缺乏可靠的根据,都分别系统地高估(或低估)了测得谱线的统计可靠性,即低估(或高估)了测得的谱线系由连续能谱背景统计涨落而来的可能性.本文导出了一个估计观测结果显著性的公式,并用蒙特卡罗模拟的结果验证了它的正确性.应用本文的方法我们重新估算了一些X及γ谱线观测结果的可靠性.     

Cyg X-3X光子场对γ射线的吸收效应

本文详细讨论了X射线双星Cyg X-3 的X光子场对γ射线的吸收效应.计算结果表明:当Cyg x-3 的X光子发射场处于高态时,从致密中子星附近发射的能量为10~2—10~4MeV的γ射线约有60％被其吸收,吸收过程产生的正负电子的逆Compton 散射会使出射能量10—70MeV的γ射线强度平均增加约50％.计算的γ射线能谱与实验观测结果基本相符.     

XTE J1550-564 2001年“迷你爆发”的X射线能谱研究

黑洞X射线暂现源的迷你爆发是一类峰值光度较低、持续时间较短的爆发.由于观测数据较少,其物理机制仍不清楚.利用RXTE (Rossi X-ray Timing Explorer)卫星从2001年1月28日到3月14日的数据,研究了黑洞X射线暂现源XTE J1550–564 2001年迷你爆发的X射线能谱特性.发现在本次迷你爆发中, XTE J1550–564的X射线能谱可以用幂律谱很好地拟合.整个爆发的硬度强度图不是标准的q型,而是一直保持在最右侧.此外,还分析了此次爆发谱指数Γ与未吸收的2–10 keV能段的X射线流量F_(2–10 keV)的相关性,发现Γ-F_(2–10 keV)呈反相关关系,且谱指数Γ∈[1.35, 1.72].上述结果表明2001年这次爆发一直处于低/硬态,它的X射线辐射主要来自于辐射低效的吸积模式,如ADAF(Advection-Dominated Accretion Flow).     

从硬X射线和微波爆发频谱推断的两种太阳耀斑高能电子谱指数的异同

从观测频谱资料出发表明谱极大两边的能谱指数在不同的模型中有不同的结果．在均匀的射电源模型下,光厚边的谱指数几乎与电子能谱指数无关;而从光薄边的谱指数得到的电子能谱指数δR远小于X射线的δX.因此均匀源模型下两者的能谱指数是不同的．在使用非均匀源模型时,无论是从光厚边还是从光薄边的潜指数,得到的电子能谱指数都是等同于X射线的,即δR=δX.这从能谱指数的角度上,从实测资料论证了两者的非热电子分布可以是同样的．并以1981年4月27日0800UT的爆发为例,计算了非均匀射电源的参数。表征磁场梯度的αB值为2．0-4.5,源中的最大磁场为207—440G,3GHz的射电源的球壳大小为（0．9-4．6）×109cm．     

High energy gamma-ray emission from the region of the galactic center

In two balloon flights carried out in the Southern Hemisphere, a region of the sky near the galactic center has been explored with a Spark Chamber telescope with the aim of investigating the gamma-ray emission at energies above 20 MeV from possible celestial sources.     

HAXTEL: A Laue lens telescope development project for a deep exploration of the hard X-ray sky (> 60 keV)

A review of the HAXTEL project devoted to the development of a Laue lens telescope for hard X-/gamma-ray observation of the continuum spectra of celestial sources is presented. Main design properties, open issues, the status of the project and an example of multi-lens configuration with sensitivity expectations are discussed.     

Ionospheric effects of transient celestial X-ray and gamma-ray events

The paper presents the results on investigations of the ionospheric effects arising out of the transient celestial events at X-ray and gamma-ray energies such as that from X-ray novae and cosmic gamma-ray bursts. The VLF data recorded at Ahmedabad corresponding to the 164 kHz transmission from Tashkent are examined to see whether there are any observable effects time coincident with the transit of the X-ray novae Cen X-4 and Cet X-2 around their intensity maxima. Besides, the VLF data have also been examined in relation to the cosmic gamma-ray bursts detected by Vela, IMP-6 and OSO-7 satellites.Theoretical computations are carried out for estimating electron density enhancements using the available data on intensities and energy spectra for these events. Further, the observational resutls are explained in terms of these theoretical calculations.Presently at Indian Space Research Organization, Bangalore, India.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

Periodicity search for possible X-ray counterparts to radio-quiet gamma-ray pulsar candidates

A periodicity search of gamma-ray data is usually difficult because of the small number of detected photons. A periodicity in the timing signal at other energy bands from the counterpart to the gamma-ray source may help to establish the periodicity in the gamma-ray emission and strengthen the identification of the source in different energy bands. However, it may still be difficult to find the period directly from X-ray data because of limited exposure. We have developed a procedure, by cross-checking two X-ray data sets, to find candidate periods for X-ray sources that are possible counterparts to gamma-ray pulsar candidates. Here, we report on the results of this method obtained with all the currently available X-ray data of eight X-ray sources. Some attractive periodicity features were found. These candidate periods can serve as the target periods for a future search when new data become available, so that a blind search with a huge number of trials can be avoided.     

Catalog of cosmic gamma-ray bursts from the KONUS experiment data

Data are presented on the temporal structure, fluxes, energy spectra and coordinates of the sources of gamma-ray bursts detected in the KONUS experiment on Venera 11 and Venera 12 space probes in the period September 1978 to May 1979. The statistical distributions of gamma bursts in duration, intensity, and peak power, as well as the distribution of the burst sources over the celestial sphere presented are based on the updated KONUS information obtained until February 1980.     

Distribution of gamma-ray bursts over the celestial sphere

The fractal dimensionality of the distribution of gamma-ray bursts over the celestial sphere has been investigated. Current data from the BATSE experiment were used. A value of D₂ ≈ 2 is obtained, corresponding to a uniform spatial distribution of burst sources. Translated from Astrofizika, Vol. 42, No. 2, pp. 219–224, April–June, 1999     

On gamma-ray emission from CYG X-2

We discuss the importance of hard X- and gamma-ray emission from thermal X-ray sources to obtain a more realistic picture of these objects.In particular, we show that the inverse Compton effect is a possible mechanism of gamma-ray emission from sources of this kind and apply our consideration to the specific case of Cyg X-2.     

Radio pulsars with expected gamma radiation and gamma-ray pulsars as pulsating radio emitters

Pulsars play a crucial astrophy sical role as highly energetic compact radio, X-ray and gammaray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope(LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log B_(lc)(G) are 3.60-3.95 and 1.75 correspondingly. Moreover,their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: log E(erg s~(-1)) = 35.37-35.53 and 32.64. The correlation between gammaray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand,the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.     

Scale transformations, tree-level perturbation theory and the cosmological matter bispectrum

Soon after the discovery of radio pulsars in 1967, the pulsars are identified as strongly magnetic (typically 10¹² G) rapidly rotating (∼10²− 0.1 Hz) neutron stars. However, the mechanism of particle acceleration in the pulsar magnetosphere has been a longstanding problem. The central problem is why the rotation power manifests itself in both gamma-ray beams and a highly relativistic wind of electron–positron plasmas, which excites surrounding nebulae observed in X-ray. Here we show with a three-dimensional particle simulation for the global axisymmetric magnetosphere that a steady outflow of electron–positron pairs is formed with associated pair sources, which are the gamma-ray emitting regions within the light cylinder. The magnetic field is assumed to be a dipole, and to be consistent, the pair creation rate is taken to be small, so that the model might be applicable to old pulsars such as Geminga. The pair sources are charge-deficient regions around the null surface, and we identify them as the outer gap. The wind mechanism is the electromagnetic induction which brings about fast azimuthal motion and eventually trans-field drift by radiation drag in the close vicinity of the light cylinder and beyond. The wind causes loss of particles from the system. This maintains charge deficiency in the outer gap and pair creation. The model is thus in a steady state, balancing loss and supply of particles. Our simulation implies how the wind coexists with the gamma-ray emitting regions in the pulsar magnetosphere.     

The frequencies of high frequency quasi-periodic oscillations in two different frames in black hole LMXBs

We discuss the modes of the Alfve'n waves in the accretion disk with a toroidal magnetic field in black hole low mass X-ray binaries in a rotating frame.By solving the perturbed general relativistic magnetohydrodynamic equations in the rotating frame,we find two stable modes of the Alfve'n wave which are the same as those in the fiducial observer frame.This gives a feasible way to transform between the two different frames,which validates the possible Alfve'n wave modes in the accreting celestial bodies wit...