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。     

r射线暴的时变分析

r射线暴是天空中突然的硬x射线r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r射线暴的时变规律是非常重要的。对7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。     

Ⅰ型X射线暴多峰结构的研究进展

Ⅰ型X射线暴(热核暴)是发生在小质量X射线中子星双星系统中X射线波段流量突然大幅度增加的一种高能现象.在热核闪模型下,此现象被认为主要由中子星表面热核不稳定燃烧主要引起的.典型X射线暴的光变曲线呈现快速上升(1～5 s)、e指数下降(10～100 s)的单峰结构.随着X射线暴样本的增加,在观测上出现了一类多峰结构的热核...     

CygX—1硬态高能光子的时延

硬X射线和软射线光子的时延时研究主能辐射的一个重要方面，傅里叶交叉谱常常被用于教育处硬软光子之间的时延，但是交叉说示能在高于30Hz的傅里叶频率上从CygX-1测量到有统计意义的快速光变，由李惕培在时域上发展的交叉相关函方法能有效测量不同时间尺度上的时延，利用此交叉相关分析方法，讨论了不同观测时期CygX-1硬态高能光子时延 的性质，分析结果表明，CygX-1硬态在短的尺度（＜0．1秒）上存存在有意义的时间延迟，并将短时间尺度上的观测结果和各种CygX-1硬态模型进行了比较讨论。     

BLazar天体的光变及多波段能谱特性

本文综述了活动星系核，特别是blazar天体的研究现状，对blazar天体的多波段与多波段能谱特性研究进行了较为详细的评述。主要的研究工作包括以下内容：（一）γ噪blazar天体的短时标光变研究，通过对16个γ噪blazar天体（其中包括全部已证认和观测到VHEγ射线爆发的可能甚高能γ射线源）自1998年的光学观测及光变分析研究表明，短时标光变（小时量级）是GeV γ噪blazar天体的普遍特性，光变幅度通常可达0.6mag/h，对PKS 1510－089类星体的观测发现在一个小时内对象变暗2个星等，对如此激烈的光变变暗目前的理论还不能很好的解释，但它同样反映了辐射区域的内部结构；而对TBLs的监测表明，其光学波段的短时标光变没有其他对象激烈，出现的频度和振幅变化都较小；（二）在研究γ噪blazar天体光变时，研究了寄主星系对光变的影响，得到了1ES 2344 514的光变与PSF的FWHM的关联，表明随着大气视宁度的下降（即FWHM变大），对象变暗，即由于寄主星系的影响从而导致假光变的产生；（三）引进两个多波段复合谱指数，αXOX=αOX-αX及αoro=αor-αo。对样本的统计研究表明，RBLs是能谱特性界于XBLs和OVVs之间的一类中间态，所得结果支持了Sambruna et al.（1996）大样本多波段能谱分布特性的统计研究结果；（四）对地面探测器对blazar天体甚高能波段的观测做了较为详细的了解，由于blazar天体在全波段上都观测到光变，所以这类对象是多波段观测研究最完全的。地面望远镜对小时量级的光变很敏感，所以，对低流量源的直到10TeV或更高能谱的测量是多波段研究的重要扩展，特别是，如果γ射线的幅射是通过康谱顿散射提升低能同步辐射光子产生的，即SSC模型产生，那么，VHEγ射线的观测和低能同步辐射的观测就可能估计喷流内的磁场强度、Doppler因子等。对我们今后的光学波段的观测工作提出了新的课题。     

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。     

相对论电子的物理效应及其在高能天体中的应用

本文对相对论电子的辐射性质、能谱演化和加速机制等进行了简要的介绍。同时，对相对论电子在高能天体中的辐射作用和特性进行了简要的综述。本文给出了相对论电子在Blazar天体的射电辐射机制、光变机制、BL Lac天体的辐射机制以及γ暴的辐射机制等方面的应用研究成果。1、提出了相对论电子的光学薄同步辐射模型：解释Blazar天体的射电平谱：Blazar中心体的剧烈活动，使射电辐射区处于等离子体湍动状态，其中的相对论电子在湍动等离子体波的二交费米加速、激波加速、辐射损失、粒子逃逸和辐射区的绝热减速等物理过程作用下，形成较平的能谱，产生射电平谱。2、提出了新的Blazar天体光变模型：当Blazar天体爆发时，中心天体产生大量的相对论电子，注入喷流中；相对论电子产生同步辐射，并不断损失能量和逃逸辐射区，使它们的能谱快速变化，引起辐射发生快速光变。3、给出了BL Lac天体的等离子体反应堆模型：大量相对论电子从中心天体注入周围的等离子体反应堆中，通过同步辐射快速损失能量，同时这些电子同步吸收反应堆中不透明的光子，产生一个稳定、各向同性的幂律分布，其谱指数为γ＝3；然后，这些相对论电子通过等离子体反应堆的爆发或其表面扩散过程逃逸出来，辐射低频的同步辐射。模型解释了BL Lac天体的高频辐射表现出快速的谱变化性质，即流量减小时谱变陡。4、提出了相对论电子的内激波加速模型，解释γ暴的尖峰光变特性：在γ暴产生的相对论运动的壳层中，有内激波产生；激波在壳层中传播，耗散壳层的运动能，使其中的部分电子加速成为相对论电子。然后，这些电子通过同步辐射产生观测到的γ辐射。模型认为，γ暴中的每个尖峰辐射是一对内激波加速相对论电子的辐射过程，复杂的γ暴光变曲线是多对内激波辐射过程的叠加。     

成像硬X射线望远镜在美国和欧洲的发展

硬X射线能带（20KeV-1MeV)是我们了解天体物理中高能辐射过程的一个好窗口。成像硬X射线望远镜可以提供更好的分辨率和灵敏度来研究硬X射线天体物理学。本文介绍了成像硬X射线望远镜在美国和欧洲的发展，这包括：1）EXITE2，由美国哈佛－史密松林天体物理中心设计和运行的一个光电开关成像硬X射线望远镜；2）EXIST，一个成像硬X射线全天巡天望远镜，将于2010年由ULDB（EXIST－LINE）或国际空间站（EXIST－ISS）承载；3）HERO，由NASA／MSFC建造的一个新的硬X射线光学仪器。     

Blazars的聚束效应

本文对Blazars的聚束效应及相关的理论作了较全面的综述，指出了一 些有待进一步探讨的问题和需要进一步完善的理论，并对其中几个具体问题进行研究，得到了一些新结果。第一章简单介绍了活动星系核的特征、分类及其标准模型。第二章综述了Blazars的基本性质、对Blazars的谱特征、高光度、高偏振、激烈光变、超光速现象和高能辐射等作了介绍。第三章介绍了相对论喷流模型，以及利用相对论喷流模型解释Blazars的极端观测特性，如用相对论喷流模型从理论上解释了Blazars的高光度、剧烈光变及高能量转换率，偏振方向的快速变化，超光速现象，发射线和高能辐等能观测特性。同时介绍了喷流具有相对论性的观测证据并重点介绍了喷流的加速和减速两个理论模型。第四章是聚束效应的几项具体研究工作，首先分析了28个BL Lac天体，24个核优势高偏振类星体，29个核优势低偏振类星体，以及11个瓣优势低偏振类星体的射电和光学流量，证实具有相对论喷流的AGNs的Doppler提升效应确实存在，且很明显，光学和射电是高度聚束的。最小光变时标是一个及其重要的物理理，短时标光变能给人们提供大量的信息。但最小光变时标一般是在不同波段探测到的。利用加速模型，我们从理论上导出了一个联系各波段最小光变时标的公式，可把观测到的不同波段最小光变时标转换为同一波段的最小光变时标。利用该公式，把观测到的29个Blazars的不同波段最小光变时标转换为γ波段的最小光变时标，我们分析了这些对象光度与光变时标的关系，证实了Blazars的γ射线是高度聚束的。我们还研究了Blazars的偏振，发现偏振也是和聚束效应密切相关的，对Blazars的高能辐射也作了一些探讨，发现同步自康普顿模型能较好的解释Blazars天体的γ辐射。另外，提出一个新的喷流的电子注入模型，成功的解释了射电选Blazars天体在爆发时的谱硬化现象。     

成像硬X射线望远镜在美国和欧洲的发展

硬X射线能带 (2 0KeV～ 1MeV)是我们了解天体物理中高能辐射过程的一个好窗口。成像硬X射线望远镜可以提供更好的分辨率和灵敏度来研究硬X射线天体物理学。本文介绍了成像硬X射线望远镜在美国和欧洲的发展 ,这包括 :1 )EXITE2 ,由美国哈佛———史密松林天体物理中心设计和运行的一个光电开关成像硬X射线望远镜 ;2 )EXIST ,一个成像硬X射线全天巡天望远镜 ,将于 2 0 1 0年由ULDB (EXIST -LINE)或国际空间站 (EXIST -ISS)承载 ;3)HERO ,由NASA/MSFC建造的一个新的硬X射线光学仪器。     

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．     

Concept of High Speed Astronomical Instrumentation Based on Visible Light Photon Counters

The domain of high speed optical astrophysics is still quite unexplored. The availability of 10 meter diameter telescopes offers the unique possibility to investigate variability of faint objects at submillisecond time scales. In this paper I describe the concepts of a photometer and a spectrometer for high speed astronomical observations. The instruments are based on a photon counting detector developed for high energy physics, the Visible Light Photon Counter (VLPC). The detector has a quantum efficiency in the visible as high as 88% and performs photon counting with sub microsecond time resolution. The photometer is built using VLPC arrays. Adding a grating a VLPC array can be used in a time resolved spectrograph with medium resolution. This paper develops, starting from experimental data, the concept of the two VLPC based instruments and their application to time resolved photometry and spectroscopy of compact objects (pulsars, cataclysmic variables, low mass X-ray binary systems etc) and optical counterparts of Gamma Ray Bursts. The high speed optical observations are the ideal complement to X/γ rays and gravitational wave studies. The application of the instruments to the optical photometry of pulsars, the spectrophotometry of the prompt optical flash from Gamma Ray Bursts and the study of binary systems are discussed in detail: in the last two applications the instruments offer better opportunities than existing instruments.     

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.     

PheniX: a new vision for the hard X-ray sky

We are proposing a mission devoted to high energy X-ray astronomy that is based on a focusing telescope operating in the 1?C200?keV energy range but optimized for the hard X-ray range. The main scientific topics concern: Physics of compact objects: The proximity of compact objects provides a unique laboratory to study matter and radiation in extreme conditions of temperature and density in strong gravitational environment. The emission of high energy photons from these objects is far from being understood. The unprecedented sensitivity in the high energy domain will allow a precise determination of the non-thermal processes at work in the vicinity of compact objects. The full 1?C200?keV energy coverage will be ideal to disentangle the emission processes produced in the spacetime regions most affected by strong-gravity, as well as the physical links: disk?Cthermal emission?Ciron line?Ccomptonisation?Creflection?Cnon-thermal emission?Cjets. Neutron stars?Cmagnetic field?Ccyclotron lines: Time resolved spectroscopy (and polarimetry) at ultra-high sensitivity of AXP, milliseconds pulsars and magnetars will give new tools to study the role of the synchrotron processes at work in these objects. Cyclotron lines?Cdirect measurement of magnetic filed?Cequation of state constraints?Cshort bursts?Cgiant flares could all be studied with great details. AGN: The large sensitivity improvement will provide detailed spectral properties of the high energy emission of AGN??s. This will give a fresh look to the connection between accretion and jet emission and will provide a new understanding of the physical processes at work. Detection of high-redshift active nuclei in this energy range will allow to introduce an evolutionary aspect to high-energy studies of AGN, probing directly the origin of the Cosmic X-ray Background also in the non-thermal range (> 20?keV). Element formation?CSupernovae: The energy resolution achievable for this mission (<0.5?keV) and a large high energy effective area are ideally suited for the 44Ti line study (68 and 78?keV). This radioactive nuclei emission will give an estimate of their quantities and speed in their environment. In addition the study of the spatial structure and spectral emission of SNR will advance our knowledge of the dynamics of supernovae explosions, of particles acceleration mechanisms and how the elements are released in the interstellar medium. Instrumental design: The progress of X-ray focusing optics techniques allows a major step in the instrumental design: the collecting area becomes independent of the detection area. This drastically reduces the instrumental background and will open a new era. The optics will be based on depth-graded multi-layer mirrors in a Wolter I configuration. To obtain a significant effective area in the hundred of keV range a focal length in the 40?C50 meters range (attainable with a deployable mast) is needed. In addition such a mission could benefit from recent progress made on mirror coating. We propose to cover the 1?C200?keV energy range with a single detector, a double-sided Germanium strip detector operating at 80?K. The main features will be: (a) good energy resolution (.150?keV at 5?keV and <.5?keV at 100?keV), (b) 3 dimensional event localization with a low number of electronic chains, (c) background rejection by the 3D localization, (d) polarisation capabilities in the Compton regime.     

An optical view of BL Lacertae objects

BL Lac objects are active nuclei, hosted in massive elliptical galaxies, the emission of which is dominated by a relativistic jet closely aligned with the line of sight. This implies the existence of a parent population of sources with a misaligned jet that have been identified with low-power radiogalaxies. The spectrum of BL Lacs, dominated by non-thermal emission over the whole electromagnetic range, together with bright compact radio cores, high luminosities, rapid and large amplitude flux variability at all frequencies and strong polarization makes these sources an optimal laboratory for high energy astrophysics. A most distinctive characteristic of the class is the weakness or absence of spectral lines, that historically hindered the identification of their nature and ever thereafter proved to be a hurdle in the determination of their distance. In this paper, we review the main observational facts that contribute to the present basic interpretation of this class of active galaxies. We overview the history of the BL Lac objects research field and their population as it emerged from multi-wavelength surveys. The properties of the flux variability and polarization, compared with those at radio, X-ray and gamma-ray frequencies, are summarized together with the present knowledge of the host galaxies, their environments, and central black hole masses. We focus this review on the optical observations, which played a crucial role in the early phase of BL Lacs studies, and in spite of extensive radio, X-ray, and recently gamma-ray observations, could represent the future major contribution to the unveiling of the origin of these sources. In particular, they could provide a firm conclusion on the long debated issue of the cosmic evolution of this class of active galactic nuclei and on the connection between formation of supermassive black holes and relativistic jets.     

HESS observations of extragalactic objects

The HESS experiment (High Energy Stereoscopic System), consisting of four imaging atmospheric Cherenkov telescopes (IACTs) in Namibia, has observed many extragalactic objects in the search for very high energy (VHE) γ-ray emission. These objects include active galactic nuclei (AGN), notably Blazars, Seyferts, radio galaxies, starburst galaxies and others. Beyond the established sources, γ-ray emission has been detected for the first time from several of these objects by HESS, and their energy spectra and variability characteristics have been measured. Multi-wavelength campaigns, including X-ray satellites, radio telescopes, and optical observations, have been carried out for AGNs, in particular for PKS 2155-304, H 2356-309 and 1ES 1101-232, for which the implications concerning emission models are presented. Also results from the investigations of VHE flux variability from the giant radio galaxy M 87 are shown. For the HESS Collaboration.     

Investigating a fluctuating-accretion model for the spectral-timing properties of accreting black hole systems

The fluctuating-accretion model of Lyubarskii and its extension by Kotov, Churazov & Gilfanov seek to explain the spectral-timing properties of the X-ray variability of accreting black holes in terms of inward-propagating mass accretion fluctuations produced at a broad range of radii. The fluctuations modulate the X-ray emitting region as they move inwards and can produce temporal-frequency-dependent lags between energy bands, and energy-dependent power spectral densities (PSDs) as a result of the different emissivity profiles, which may be expected at different X-ray energies. Here, we use a simple numerical implementation to investigate in detail the X-ray spectral-timing properties of the model and their relation to several physically interesting parameters, namely the emissivity profile in different energy bands, the geometrical thickness and viscosity parameter of the accretion flow, the strength of damping on the fluctuations and the temporal coherence (measured by the 'quality factor', Q ) of the fluctuations introduced at each radius. We find that a geometrically thick flow with large viscosity parameter is favoured, and we confirm that the predicted lags are quite robust to changes in the emissivity profile and physical parameters of the accretion flow, which may help to explain the similarity of the lag spectra in the low/hard and high/soft states of Cyg X-1. We also demonstrate the model regime where the light curves in different energy bands are highly spectrally coherent. We compare model predictions directly to X-ray data from the narrow line Seyfert 1 galaxy NGC 4051 and the black hole X-ray binary (BHXRB) Cyg X-1 in its high/soft state, and we show that this general scheme can reproduce simultaneously the time lags and energy-dependence of the PSD.     

Rms–flux relation of Cyg X-1 with RXTE: dipping and nondipping cases

The rms (root mean square) variability is the parameter for understanding the emission temporal properties of X-ray binaries (XRBs) and active galactic nuclei (AGN). The rms–flux relation with Rossi X-ray Timing Explorer (RXTE) data for the dips and nondip of black hole Cyg X-1 has been investigated in this paper. Our results show that there exist the linear rms–flux relations in the frequency range 0.1–10 Hz for the dipping light curve. Moreover, this linear relation still remains during the nondip regime, but with the steeper slope than that of the dipping case in the low energy band. For the high energy band, the slopes of the dipping and nondipping cases are hardly constant within errors. The explanations of the results have been made by means of the “Propagating Perturbation” model of Lyubarskii (Lyubarskii, Y.E., Mon. Not. Roy. Astron. Soc. 292, 679–685 (1997)).     

On the Nature of the Variable Gamma-Ray Sources at Low Galactic Latitudes

Population studies of EGRET gamma-ray sources indicate that there is a distinctive population of bright sources at low galactic latitudes. The sources have a distribution consistent with that of young galactic objects, with a concentration toward the inner spiral arms. There is a subgroup that displays strong variability with timescales from days to months. Following an earlier suggestion by Kaufman Bernadó et al. (2002), we explore the possibility that these sources could be high-mass microquasars. Detailed models for the gamma-ray emission that include inverse Compton interactions of electrons in the relativistic jets and photons from all local fields (stellar UV photons, synchrotron photons, soft X-ray photons from the accretion disk, and hard X-ray photons from a corona) are presented. We conclude that microquasars are excellent candidates for the parent population of the subgroup of variable low-latitude EGRET sources.