YNAO OpenIR  > 星系研究组
BL Lac天体的光变
白金明
Subtype博士
Thesis Advisor谢光中
1999
Degree Grantor中国科学院云南天文台
Place of Conferral昆明
Keyword活动星系核 Bl Lac天体 喷流 光变 观测 理论模型
Abstract大幅、快速光变是BL Lac天体的定义特征之一,光变研究一直是BL Lac天体研究的重要内容。本论文对BL Lac天体的光变研究成果和BL Lac天体的基本理论以及一些相关的其它研究方向的成果作了较为全面的总结,指出了目前研究中存在一些不足或可以进一步发展之处,并对其中的几个问题进行了研究。全文共分七章。第一章介绍了光变研究的意义和BL Lac天体光变研究的概况,着重总结和比较了光变研究的方法。第二章简单介绍了活动星系核的特征、分类等与BL Lac天体有关的基本知识,着重介绍活动星系核的能源机制-吸积释能,和活动星系核的基本模型。第三章在介绍了BL Lac天体的基本性质之后,简单介绍了BL Lac天体的的能谱分布及其主要辐射机制研究的最新进展,着重介绍了目前比较公认的BL Lac天体的理论模型-相对论喷流模型及其推论-BL Lac天体与射电星系的统一模型及其最近的研究动态;指出,和BL Lac天体与其母体星系的统一相比,BL Lac天体自身的统一对相对论喷流理论而言同样具有重要的理论意义。第四章总结了BL Lac天体短时标光变从射电到γ射线的各波段的观测研究成果;归纳出了BL Lac天体短时标光变的特征并介绍了解释这些特征的理论模型-激波模型,指出突然大幅变暗现象虽不如闪耀等突然变亮现象频繁但也是一种普遍的短时标光变现象,对激波模型是一个挑战;指出射电宁静的活动星系核的短时标光变研究有助于揭示BL Lac天体的非喷流起源的短时标光变的产生机制。作为一个例子,本章的最后介绍了我们在短时标光变方面的一项已发表的研究工作(即附录三),我们用光学波段和TeVγ波段的短时标光变观测资料对著名BL Lac天体Mrk 421中心核区进行了研究。第五章总结了BL Lac天体长时标光变的特征,着重介绍了长时标光变的周期性研究,以及对著名BL Lac天体OJ287周期性大爆发的证实,指出BL Lac天体长时标光变的周期性很可能具有普遍性,很可能是本质上与短时标光变不同的两种光变现象,两者具有不同的产生机制,指出了现有长时标光变理论模型(激波模型)的困难,简单介绍了最近提出的新模型;指出长时标光变的研究将有可能揭示活动星系核的较大尺度结构,如喷流与中心核区的物质和能量联系,证明吸积盘的存在等。第六章是我们的另一项已发表的研究工作(即附录一)。通过对射电选BL Lac天体与X射线选BL Lac天体短时标光变的对比观测研究,我们比较了XBL和RBL的短时标光变的差别,并与BL Lac天体统一模型的预言进行了比对,检验了统一模型。本章还简单介绍了同一时期国外这方面的研究,并与之进行了比较。第七章也是我们的一项已发表的研究工作(附录二)。我们比较了高态与低态下BL Lac天体短时标光变的差别,发现高态下短时标光变比低态下频繁而且幅度大。我们提出活动星系核的相对论性喷流方向会改变,从而导致长期光变;高态是喷流方向与观测者视线夹角较小的表现,而低态则是夹角较大的表现。利用该模型我们解释了BL Lac天体短时标光变行为在高态和低态下的差别,并成功地解释了OJ94国际联测计划中发现的OJ287和3C 66A的新光变现象。
Other AbstractLarge and rapid variability is one of the defining properties of BL Lac objects. Variability in BL Lac objects has always served as powerful and important tool for constraining the physics of these unusual objects. This thesis present a review for observational and theoretical studies of variability in BL Lac objects and relevant studies such as theories and models for BL Lac objects, variability in other Active Galactic Nuclei (AGN), and some of our research work in this field. There are seven chapters in this thesis altogether. Chapter One is an overview of variability study. The importances of variability study are discussed, and the most significant new progresses in the studies of variability in BL Lac objects are simply presented, together with a review of the methods and approaches for variability study. Chapter two presents some elemental knowledge of AGNs which is relevant to BL Lac objects. Since the observational study on variability aims at testing theories and models for BL Lac objects, Chapter Three mainly present theoretical study for BL Lac objects, especially, the relativistic jet model and the unify scheme for BL Lac objects. We point out that to unify BL Lac objects itself (say, to unify RBL and XBL, or other schemes) is as important as to unify BL Lac objects and its parent population (say FRI radio galaxies) for testing relativistic jet model, because the viewing angles should show a continuous distribution. In Chapter Four we review the studies of short timescale variability in BL Lac objects, the observations from radio to γ-rayds, the multirange observation, the conections to other properties of BL Lac objects, the characteristics of short timescale variability, the differences with the variability in other AGNs and the theoretic models, in particularly, shocks-in-jet model. We point out that the abrupt short-term drops which are also common in BL Lac objects, though not as frequent as flares, is a powerful challenge to shocks-in-jet model, and that the investigation for variability in radio-quiet AGNs may help to reveal the mechanisms for those short timescale variations which do not originate in the relativistic jet of BL Lac objects. Chapter Five reviews long timescale variability in BL Lac objects, long term monitoring, the characteristics of long timescale variability, especially the periodicity and the confirming observation during OJ 94 program, and the theoretic models for long timescale variability. We point out that the fact that almost all BL Lac objects which have light curve with long time span show periodicity for long timescale variability indicates that long timescale variability is somewhat different from short timescale variability which is irregular, and that it is difficulties for shocks-in-jet model to explain periodicity in long term variability, even though the model has been revised to have a lighthouse effect. New models proposed to explain periodicity are summarized at the of this Chapter. We point out that studies of long timescale variability may reveal the large scale structure of AGNs, such as the transportation of energy and matter from the central region to relativistic jet, the existence of accretion disk. In Chapter Six our work which compares the behaviour of short timescale variability in radio-selected and X-ray-selected BL Lac objects is presented to test the unify scheme. The results of our work do not support different viewing angle scenario. In Chapter Seven we present our studies of difference of short timescale variability between the high states and low states of BL Lac objects. We find that the BL Lac objects in our sample show stronger activity with more small flares and flickers in high state than in low state. We suggest that the orientation of the relativistic jet of a BL Lac object changes with the time, and thus cause the variability on long timescale. The high state of a BL Lac object is when the jet is closer to line of sight, and the low state is when the jet is away from the line of sight. In this scenario we explained the difference between variability on short timescale in the high state and low state of BL Lac objects, and the new phenomena in OJ 287 discovered in OJ 94 program by Takalo et al.
Subject Area天文学
Pages112
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/7147
Collection星系研究组
Recommended Citation
GB/T 7714
白金明. BL Lac天体的光变[D]. 昆明. 中国科学院云南天文台,1999.
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