【作者】 张晋；

【导师】 白金明；

【作者基本信息】 中国科学院研究生院（云南天文台） ， 天体物理， 2009， 博士

【摘要】 活动星系核（AGN）是存在着猛烈活动现象星系的核心。随着探测设备角分辨率和灵敏度的提高,活动星系核及其延展结构在射电、红外、光学、X射线等波段被探测到,分辨出其更细致的结构,如喷流、喷流的节点、射电瓣和热斑等。空间和地面高能望远镜也在MeV-GeV-TeV能段探测到许多源的高能辐射,对AGN的辐射机制给出了强的限制。活动星系核及其延展区的高能辐射成为当今极其活跃的研究领域。本文简述了AGN及其延展结构的观测和理论研究进展,并详实地报告了攻读博士学位期间的研究工作。至今,被证认是TeV源的AGNs中除了两个射电星系（Cen A和M87）之外都是blazars,而且绝大多是高峰频的BL Lac天体（HBL）。W Comae是最近被证认的第一个具有TeV辐射的中峰频BL Lac天体（IBL）。我们用均匀单辐射区的同步+同步自康普顿辐射（Syn+SSC）模型研究了该天体从射电到TeV能段的SED,发现该模型能够很好地解释其多波段的观测能谱,且高能伽玛射线辐射是由SSC贡献的,并揭示X射线/光学能段和TeV能段高态不一定同步。射电热斑是喷流的终点,通常认为由喷流与周围介质碰撞形成,很可能是高能粒子的加速场所。这些高能的相对论电子通过SSC过程就可能产生高能的伽玛射线辐射,甚至TeV伽玛射线辐射。我们选取Pictor A的西边热斑作为研究对象,分析该热斑从射电到X射线能段的SED,研究其X射线辐射机制。我们发现这个源的SED很难用单一辐射区域的Syn+SSC模型拟合,进而提出这个热斑本身可能还有更进一步的空间结构,并用多辐射区模型很好地拟合了观测的SED。这结果跟Tingay等人（2008）的VLBI的观测是一致的。在非能均分磁场条件下,模型预言了较强的GeV-TeV辐射,并且通过比较热斑和核区的SED发现这个源的GeV-TeV高能辐射主要来自该热斑的贡献而不是核区。在此基础上,我们进一步系统地研究了喷流节点和热斑的高能辐射性质,并比较两类延展结构物理性质的本质差异性。我们选择了一个包括21个热斑和46个节点的样本,系统地分析了它们的观测特征。这些节点和热斑的能谱分布覆盖了射电、光学和X射线,可以较好地限制辐射机制模型。我们用单区模型拟合这些SEDs,发现热斑和节点的X射线辐射机制可能是多样化的。一少部分热斑和节点的X射线辐射是由同步辐射产生的,但是对大部分源来说需要一个逆康普顿成分解释观测到的X射线辐射。不考虑聚束（beaming）效应时,用SSC模型拟合观测的X射线流量,热斑的拟合磁场强度B_SSC^δ=1对能均分磁场值B_eq^δ=1的偏离不超过一个量级,而节点的B_SSC^δ=1远远偏离了能均分磁场。我们定义了一个描述偏离能均分磁场程度的量R_B=B_eq^δ=1/B_SSC^δ=1,发现R_B和光度比RL≡L_1keV/L_5GHz是强反相关的,尤其是对于节点。考虑聚束效应时,在能均分条件下,相对论电子逆康普顿散射微波背景光子（IC/CMB）模型可以很好地解释热斑和节点的X射线辐射。这种情况下,热斑和节点的能均分磁场值在相同的量级,δ和光度比RL是反相关的。这些结果表明热斑和节点X射线观测的不同是由于聚束效应造成的。SSC模型和IC/CMB模型都预言了一些源有GeV-TeV的高能辐射,而且预言流量在Fermi/LAT和HESS观测灵敏度之上。更多还原

【Abstract】 Active galactic nuclei （AGNs） are the centers of galaxies with violent activities.With great improvements in both the space resolution and detectionsensitivity, AGN jets and their sub-structures, including knots, hot spots, andlobes were observed in the radio, infrared, optical, and X-ray bands for manyAGNs. Emission in the MeV-GeV-TeV band has also been detected for someAGNs with space and ground-based telescopes, placing strong constraints on theradiation mechanisms of the AGNs. Research on the high energy emission ofAGNs and their extended regions is one of the most active fields in astrophysics.This thesis first presents a detail review on the observational and theoreticalprogress for AGNs and their sub-structures, and then reports my relevant worksin this field.So far, almost all identified TeV AGNs are blazars, the only exceptionsbeing two radio galaxies （Cen A and M87）, and most of them are HBLs. WComae was the first IBL, which was confirmed to be a TeV source. The SEDsquasi-simultaneously obtained during the TeV flare and during the optical/X-rayoutburst are well fitted by a single-zone synchrotron + synchrotron-self-Compton（Syn+SSC） model. We find that the 7-ray emission can be describedSSC leptonic jet model and the TeV flare and the X-ray/optical outburst maybe not simultaneous.It is believed that hot spots are the terminals of jets. They may be due to theinteraction of a jet with surrounding medium, and are the sites for reaccelerationof relativistic electrons. These electrons may be able to produce high energyγ-ray photons through inverse Compton （IC） scattering. We study the radiationmechanism of the X-rays from the western hot spot of Pictor A, a nearby FR IIradio galaxy, and investigate the possible GeV-TeV emission from this hot spot.We find that the single-zone Syn+SSC model can not describe the ultravioletdata well and the multi-zone model presents a much better fit, consistent withthe VLBI observation by Tingay et al. （2008）. Both the single-zone and multi- zone models predict Pictor A as a GeV-TeV source if deviating the equipartitioncondition, which could be marginally detectable with Fermi/LAT and HESS. Bycomparing the GeV-TeV flux from the nucleus and from the hot spot predictedby the model, we show that the GeV-TeV flux is dominated by the hot spot.Based on our results of the hot spot in Pictor A, we make a systematicalanalysis for a sample of 21 hot spots and 46 knots in order to investigate theradiation mechanisms of the X-rays and the physical differences between thetwo kinds of extended structures. Their radiation mechanisms can be well constrainedwith the observed SEDs that cover the radio, optical, and X-ray bands.The single-zone model fits to the observed SEDs show that the mechanisms forthe X-ray emission from the hot spots and the knots could be diverse. The X-rayemission for a small fraction of the hot spots and knots can be explained withthe synchrotron radiation, but an IC scattering component is required to modelthe X-rays for most the hot spots and knots. Without considering the beamingeffect, the X-rays of some hot spots can roughly be explained by the SSC modelwith a magnetic field strength no more than an order of magnitude smaller thanthe equipartition magnetic field, but the derived B_SSC^δ=1 significantly deviates fromB_eq^δ=1 for knots. Measuring this deviation with a ratio R_B=B_eq^δ=1/B_SSC^δ=1, we findthat R_B is strongly correlated with R_L for both the knots and hot spots, especiallyfor the knots, where R_L = L_1keV/L_5GHz. Considering the beaming effect,an IC/CMB model well explains the X-ray emission under the equipartition condition,and the derived B+_eq in this scenario are in the same order for both theknots and hot spots. Theδand R_L are correlated. Our results indicate thatthe differences on the X-ray observations for the knots and hot spots may bedue to the beaming effect if the magnetic filed for the knots and hot spots agreewith the equipartition condition. Both the SSC and IC/CMB dominated modelspredict a prominent GeV-TeV component in the SEDs for some sources, whichare detectable by HESS and Fermi/LAT.更多还原