摘要
大幅、快速光变是BLLac天体的定义特征之一 ,光变研究一直是BLLac天体研究的重要内容。本文对BLLac天体的光变研究成果和BLLac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的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BLLac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BLLac天体有关的基本知识 ,着重介绍了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BLLac天体的基本性质之后 ,简单介绍了BLLac天体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BLLac天体的理论模型—相对论喷流模型及其推论—BLLac天体与射电星系的统一模型及其最近的研究动态 ;指出 ,和BLLac天体与其母体星系的统一相比 ,BLLac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BLLac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BLLac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?
Large and rapid variability is one of the defining properties of BL Lac objects.Variability in BL Lac objects has always served as a 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 importance of variability study is 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-rays,the multirange observation,the connections to other properties of BL Lac objects,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 to be not as frequent as flares,are 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,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 which indicates that long timescale variability is somewhat different from short timescale variability which is irregular,and that it is difficult 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 this Chapter.We point out that studies of long timescale variability may reveal the large scale structure of AGNs,such as the tramsportation of energy and matter from the central region to relativistic jet,the existence of accretion disk.In Chapter Six the behaviour of short timescale variability in radio-selected and X-ray-selected BL Lac objects is compared 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.It is found that the BL Lac objects in our sample show stronger activity with smaller flares and flickers in high state than that in low state.It is suggested that the orientation of the relativistic jet of a BL Lac object changes with the time,and thus cause the variability on long timescale.When the jet is close to the line of the sight,a BL Lac object is in the high state and vice versa.In this scenario we explained the difference between variability on short timescale in the high state and low state of BL Lac objects respectively,and the new phenomena in OJ 287 discovered in OJ 94 program by Takalo et al.
出处
《云南天文台台刊》
CSCD
2000年第1期58-60,共3页
Publications of the Yunnan Observatoty
关键词
BL
Lac天体
光变
研究成果
激波模型
active galaxy nuclei
BL Lac objects
jets
variability
theoretical model
