活动星系统中相对论电束的物理效应

本文研究了Ｂｌａｚａｒ天体的辐射性质，提出一种新的喷流模型，即具有幂律分布的极端相对论电子团从中心核注入喷流等离子体中，它在一定的注入速度下，不仅能在喷流等离子体中激发等离子体湍动，产生电磁波的相干辐射，而且产生强的同步辐射，利用等离子体的弱湍理论，我们研究了极端相对论电子力在喷流等子体中的辐射过程，并详细研究了它在解释Ｂｌａｚａｒ天体辐射特性中的应用，本文认为，Ｂｌａｚａｒ天体的不稳定辐射与极端     

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。     

Blazar天体射电爆发的持续注入喷流模型

为了解释Ｂｌａｚａｒ天体射电爆发的普遍演化特性，本提出一个持续注入的喷流模型。假定在喷流基底上以相对论性速度持续地注入相对论等离子体（由磁场和相对论电子组成）。这一等离子体在沿喷流向外运动时经受绝热膨胀损耗。理论计算表明，射电爆发的频谱演化具有Ｖａｌｔａｏｊａ等人所建议的典型的３阶段演化形式。它们非常好地重现了Ｂｌａｚａｒ天体中观测到的射电爆发的普遍行为。     

BL Lac天体的谱性质

研究了等离子体反应堆模型,统一解释活动星系核的辐射性质,特别是ＢＬＬａｃ天体的谱性质．具体的物理过程是: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,产生低频的同步辐射;来自等离子体反应堆的高频辐射表现出快速的谱变化,即流量减小时谱变陡．另外,还详细分析了具有辐射损失和相对论电子注入的同步辐射源的性质．     

Blazar天体中光学射电大爆发的频谱演化

本文讨论Ｂｌａｚａｒ天体中光学射电大爆发频谱演化的理论模型．考虑沿喷流传播的相对论性激波所注入或加速的相对论性电子，受到康普顿、同步辐射和绝热膨胀三种损耗，并计及相对论电子能谱的高能截断．假定喷流轴线与观测者方向构成很小角度．文中给出了大爆发频谱三阶段连续演化的特性，即康普顿阶段，同步辐射阶段和绝热膨胀阶段的爆发特性．频谱演化用（Ｓｍ－ｖｍ）关系表达（见图２，图中Ｓｍ为频谱反转流量，ｖｍ为反转频率），它与一些Ｂｌａｚａｒ天体中观测到的典型形式相符合．     

BLLac天体的谱性质

研究了等离子体反应堆模型,统一解释活动星系核的辐射性质,特别是ＢＬＬａｃ天体的谱性质,具体的物理过程是：大量相对论电子从中心天体注入周转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遥光子,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反应堆的爆发发或其表面扩散过程逃逸出来,产生低频的同小辐射;来自等离子体反应堆的高频辐射表现出快速的     

BLO0716＋71非热辐射的喷流模型：从射电到γ射线

本文探讨用相对论喷流模型解释ＢＬ Ｌａｃ天体０７１６＋７１从射电到γ射线的整修电磁波段的非热辐射。喷流的结构分两个区域描述：内区具有抛物线结构，喷流是加速的；外区具有圆锥形结构，喷流速度恒定。相对论电子的密度和最高能量，以及磁场等参数随距离向外按幂律下降。在此模型中，射电至紫外线起源于相对论电子的同步辐射，而高能的Ｘ射线和γ射线则起源于自康普顿散射。辐射的频率越高，产生区域越靠近中央能源机器。辐射     

γ射线噪Blazar天体中尘埃的作用

利用具有多波段谱指数及流量观测资料的５９ 个Ｂｌａｚａｒ 天体作为样本,我们研究了各波段流量之间,谱指数之间的可能的相关性。新的可能的限制已从理论上进行了深入地讨论。结果暗示：（１） 同步自康普顿机制是Ｂｌａｚａｒ 天体γ射线辐射的主要机制。（２） 相对论电子与吸收积盘热光子的逆康普顿散射是Ｂｌａｚａｒ 天体γ射线产生的另一个重要机制。（３）ＢＬＬａｃ 天体不是“纯非热辐射”的天体,它们也具有强的热辐射。     

Blazar天体射电爆发的持续注入喷流模型

为了解释Blazar天体射电爆发的普遍演化特性，本文提出一个持续注入的喷流模型．假定在喷流基底上以相对论性速度持续地注入相对记等离子体（由磁场和相对论电子组成）．这一等离子体在沿喷流向外运动时经受绝热膨胀损耗．理论计算表明，射电爆发的频谱演化具有Valtaoja等人所建议的典型的3阶段演化形式.它们非常好地重现了Blazar天体中观测到的射电爆发的普遍行为．     

活动星系核射电延展区观测和理论研究

随着探测设备角分辨率和灵敏度的提高,喷流、喷流节点和热斑等活动星系核延展结构在射电、红外、光学、X射线等越来越多的波段被探测到,分辨出其更细致的结构,促进了理论研究热潮的兴起,使该领域成为当今天体物理研究的活跃领域之一。喷流是由活动星系核中心产生的准直等离子体外流,由中心黑洞驱动。至今,对喷流的成分、产生、准直原理和加速机制等基本问题并不清楚。另一方面,对于喷流、喷流节点和热斑等活动星系核延展区的辐射机制,一般认为其射电和光学辐射由相对论电子的同步辐射产生,但X射线的起源就存在着一定的争议。简单概述该领域近年来观测和理论研究进展。     

A quantitative model of coherent,stimulated emission in astrophysical jets

On the basis of issues raised by observations of BL Lac objects and the qualitative jet model proposed by Bakeret al. in 1988, we have been led to consider the quantitative role of coherent, stimulated emission in jets and construct a new jet model of blazars in which a relativistic electron beam with an axial symmetric, power-law distribution is injected from the central engine into the jet plasma. We study quantitatively the synchrotron emission of the relativistic electron beams. Using the weak turbulent theory of plasma, we discuss the interaction between relativistic electron beams and jet plasma, and the roles of stimulated emission. The main results are:

1. The synchrotron emission increases sensitively with the increase of the angle between the direction of the beam and the magnetic field. When the direction of the beam is vertical to the magnetic field, the synchrotron emission reaches its maximum, i.e. the emitted waves are beamed in the direction of the jet axis. We suggest that radio selected BL Lac objects belong to this extreme classification.
2. The synchrotron emission of the relativistic beam increases rapidly with the increase of the Lorentz factor of the relativistic electron,γ, whenγ ≤ 22.5, then decreases rapidly with increase ofγ.
3. The stimulated emission also increases with increasing Lorentz factorγ of the relativistic electrons whenγ ≤ 35 and then decreases with the increasingγ. The maximum stimulated emission and the maximum synchrotron emission occur at different frequencies. Stimulated emission is probably very important and reasonable flare mechanism in blazars.
4. The rapid polarization position angle (PA) swings may arise from the interaction between the relativistic electron beam and the turbulent plasma.

     

On the content of cold electrons in blazar and microquasar jets

We explore the possibility of determining the corpuscular composition of the plasma in the relativistic jets of blazars and microquasars from data on the polarization and intensity of their radio synchrotron emission. We have constructed a universal diagram that allows the relative content of nonrelativistic electrons to be established in specific objects using information about their frequency spectra and polarization at individual frequencies. As a result, we have found that the electron plasma component in the jets of the blazars 3C 279 and BL Lac is relativistic. In the jets of the microquasar GRS 1915+105, the cold plasma density may be comparable to or considerably higher than the relativistic particle density.     

The power of blazar jets

We estimate the power of relativistic, extragalactic jets by modelling the spectral energy distribution of a large number of blazars. We adopt a simple one-zone, homogeneous, leptonic synchrotron and inverse Compton model, taking into account seed photons originating both locally in the jet and externally. The blazars under study have an often dominant high-energy component which, if interpreted as due to inverse Compton radiation, limits the value of the magnetic field within the emission region. As a consequence, the corresponding Poynting flux cannot be energetically dominant. Also the bulk kinetic power in relativistic leptons is often smaller than the dissipated luminosity. This suggests that the typical jet should comprise an energetically dominant proton component. If there is one proton per relativistic electrons, jets radiate around 2–10 per cent of their power in high-power blazars and 3–30 per cent in less powerful BL Lacs.     

Internal shocks in the jets of radio-loud quasars

The central engine causing the production of jets in radio sources may work intermittently, accelerating shells of plasma with different mass, energy and velocity. Faster but later shells can then catch up slower earlier ones. In the resulting collisions shocks develop, converting some of the ordered bulk kinetic energy into magnetic field and random energy of the electrons which then radiate. We propose that this internal shock scenario , which is the scenario generally thought to explain the observed gamma-ray burst radiation, can also work for radio sources in general, and for blazars in particular. We investigate in detail this idea, simulating the birth, propagation and collision of shells, calculating the spectrum produced in each collision, and summing the locally produced spectra from those regions of the jet which are simultaneously active in the observer's frame. We can thus construct snapshots of the overall spectral energy distribution, time-dependent spectra and light curves. This allows us to characterize the predicted variability at any frequency, study correlations between the emission at different frequencies, specify the contribution of each region of the jet to the total emission, and find correlations between flares at high energies and the birth of superluminal radio knots and/or radio flares. The model has been applied to reproduce qualitatively the observed properties of 3C 279. Global agreement in terms of both spectra and temporal evolution is found. In a forthcoming work, we will explore the constraints that this scenario sets on the initial conditions of the plasma injected in the jet and the shock dissipation for different classes of blazars.     

Linkage between accretion disks and blazars

The magnetic field in an accretion disk is estimated assuming that all of the angular momentum within prescribed accretion disk radii is removed by a jet. The magnetic field estimated at the base of the jet is extrapolated to the blazar emission region using a model for a relativistic axisymmetric jet combined with some simplifying assumptions based on the relativistic nature of the flow. The extrapolated magnetic field is compared with estimates based upon the synchrotron and inverse Compton emission from three blazars, MKN 501, MKN 421 and PKS 2155-304. The magnetic fields evaluated from pure synchrotron self-Compton models are inconsistent with the magnetic fields extrapolated in this way. However, in two cases inverse Compton models in which a substantial part of the soft photon field is generated locally agree well, mainly because these models imply magnetic field strengths consistent with an important Poynting Flux component. This comparison is based on estimating the mass accretion rate from the jet energy flux. Further comparisons along these lines will be facilitated by independent estimates of the mass accretion rate in blazars and by more detailed models for jet propagation near the black hole.     

A theoretical unifying scheme for gamma-ray bright blazars

The phenomenology of γ-ray bright blazars can be accounted for by a sequence in the source power and intensity of the diffuse radiation field surrounding the relativistic jet. Correspondingly, the equilibrium particle distribution peaks at different energies. This leads to a trend in the observed properties: an increase of the observed power corresponds to: (i) a decrease in the frequencies of the synchrotron and inverse Compton peaks, and (ii) an increase in the ratio of the powers of the high- and low-energy spectral components. Objects along this sequence would be observationally classified respectively as high-frequency BL Lac objects, low-frequency BL Lac objects, high-polarization quasars and low-polarization quasars.   The proposed scheme is based on the correlations among the physical parameters derived in the present paper by applying to 51 γ-ray loud blazars two of the most accepted scenarios for the broad-band emission of blazars, namely the synchrotron self-Compton and external Compton models. This also explains the observational trends presented by Fossati et al., dealing with the spectral energy distributions of all blazars. This gives us confidence that our scheme applies to all blazars as a class.     

Modeling the emission processes in blazars

Blazars are the most violent steady/recurrent sources of high-energy gamma-ray emission in the known Universe. They are prominent emitters of electromagnetic radiation throughout the entire electromagnetic spectrum. The observable radiation most likely originates in a relativistic jet oriented at a small angle with respect to the line of sight. This review starts out with a general overview of the phenomenology of blazars, including results from a recent multiwavelength observing campaign on 3C279. Subsequently, issues of modeling broadband spectra will be discussed. Spectral information alone is not sufficient to distinguish between competing models and to constrain essential parameters, in particular related to the primary particle acceleration and radiation mechanisms in the jet. Short-term spectral variability information may help to break such model degeneracies, which will require snap-shot spectral information on intraday time scales, which may soon be achievable for many blazars even in the gamma-ray regime with the upcoming GLAST mission and current advances in Atmospheric Cherenkov Telescope technology. In addition to pure leptonic and hadronic models of gamma-ray emission from blazars, leptonic/hadronic hybrid models are reviewed, and the recently developed hadronic synchrotron mirror model for TeV γ-ray flares which are not accompanied by simultaneous X-ray flares (“orphan TeV flares”) is revisited. The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Stochastic Particle Acceleration in Blazar Jets

1 INTRoDUCTIONB1azars are rwho-loud AGNs characterized by emissions of strong and raPidiy wriablenOllthermal radiation over the elltire electromagntic spectrum. Syndritron ehasha followedby inverse ComPton scattering in a re1aivistic jet and beamd inio one directiOn is generallythought to be the IneCha8m powering these Objects (Kollgaard 1994; Urry & Paded 1995).All blazars have a sPectral energy distribution (SED) with tWO peak8 in a uFv rePesentation(von Montigny et al. 1995; S…     

The optical spectral slope variability of 17 blazars

Many quasi-simultaneous optical observations of 17 blazars are obtained from previous papers published over the last 19 years in order to investigate the spectral slope variability and understand the radiation mechanism of blazars. The long-period dereddened optical spectral slopes are calculated. We analyse the average spectral slope distribution, which suggests that the spectra of flat spectrum radio quasars (FSRQs) and high energy peaked BL Lac objects (HBLs) are probably deformed by other emission components. The average spectral slopes of low energy peaked BL Lac objects(LBLs), which scatter around 1.5, show a good accordance with the synchrotron self-Compton (SSC) loss-dominated model. We present and discuss the variability between the spectral slope and optical luminosity. The spectra of all HBLs and LBLs get flatter when they turn brighter, while for FSRQs this trend does not exist or may even be reversed. This phenomenon may imply that there is a thermal contribution to the optical spectrum for FSRQs. For the FSRQ 1156+295, there is a hint that the slope gets flatter at both the brightest and faintest states. Our result shows that three subclasses locate in different regions in the pattern of slope variability indicator versus average spectral slope. The relativistic jet mechanism is supported by the significant correlation between the optical Doppler factor and the average spectral slope.     

X-ray Emissions of Fermi Blazarstwo

The X-ray emissions of blazars are located at the end of synchrotron radiation and the beginning of inverse Compton radiation. Therefore, the origin of the X-ray emissions is rather complex. The spectral energy distributions (SEDs) of blazars from radio to X-ray bands can be fitted approximatively by a parabolic function. If we consider approximately the fitting curves as the physical spectra of blazars to analyze the X-ray emissions of Fermi blazars, the results show that: (1) The X-ray emissions of blazars contain two components, i.e. the synchrotron radiation and inverse Compton radiation, which can be simply separated by these fitting curves; (2) the higher the synchrotron peak frequency of the source, the greater the synchrotron radiation component, and the less the inverse Compton radiation component; (3) at 1 keV of the X-ray waveband, the synchrotron radiation component accounts for 17%, 27%, and 73% of the total X-ray emission, for FSRQs (Flat Spectrum Radio Quasars), LBLs (Low synchrotron peak frequency BL Lac objects), and HBLs (High synchrotron peak frequency BL Lac objects), respectively; (4) there is a strong positive correlation between the synchrotron peak frequency and the synchrotron radiation flux density at 1 keV, while no correlation exists between the synchrotron peak frequency and the inverse Compton radiation flux density; (5) the radiation mechanism of LBLs may be similar to that of FSRQs in the X-ray waveband.