耀变体VLBI核的光变研究
文献类型：学位论文
| 作者 | 米立功
|
| 学位类别 | 博士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院大学 |
| 授予地点 | 中国科学院新疆天文台 |
| 导师 | 刘祥 |
| 关键词 | 活动星系核 耀变体 S4 0917+624 VLBI 模型拟合 IDV 星际闪烁 |
| 其他题名 | Study on the Variability of VLBI Core of Blazars |
| 学位专业 | 理学 |
| 中文摘要 | 耀变体是活动星系核（Active Galactic Nuclei, AGN）的一个重要子类，它由平谱射电类星体（FSRQs）与蝎虎天体（BL Lac objects）组成。光变是耀变体最为显著的特征之一，耀变体在从射电波段到伽玛波段的几乎整个电磁波段都显示了极强的光变。甚长基线干涉测量（VLBI）是天文学中最重要、最有效的研究工具之一，它为活动星系核研究提供了非常高的空间分辨率。利用VLBI技术，耀变体通常能被分解为一个非常致密的核与一条单边喷流。本文重点开展耀变体VLBI核的结构与光变研究。文章的布局如下：第一章简单介绍了活动星系核的分类与统一模型；第二章介绍了VLBI技术原理与数据处理；第三章简要回顾了耀变体的光变研究；第四、第五两章重点对攻读博士学位期间的研究工作作了详细的论述；最后一章对研究工作作了总结与展望。 本文在第四章首先考察了50耀变体核在15GHz波段的长期峰值流量密度与内喷流位置角演化的相关性，重点分析了三个典型的耀变体S5 0716+714、S41807+698、[HB89] 1823+568。统计分析表明大约百分之二十的耀变体核，其峰值流量密度与主轴位置角具有相关性，包括正相关、反相关及延迟相关。基于几何束效应，我们提出了内喷流模型解释各种相关性。进一步的研究分析表明，对于一个包含78个耀变体的更大的样本，大约四分之一的耀变体核，其峰值流量密度与主轴位置角具有显著的线性相关。 我们也考察了长期的耀变体子类核的峰值流量密度与主轴位置角的变化，研究表明Fermi LAT（Large Area Telescope）证认的伽玛噪耀变体，其核具有更强的光变且内喷流的位置角改变量大于Fermi LAT未证认的伽玛噪耀变体。利用功率谱密度函数法，我们也对59个耀变体的光变曲线进行了周期分析，结果表明这59个耀变体的光变曲线显示了从2.6年到11.1年的可能的光变周期。 第五章探讨了一个典型的耀变体S4 0917+624的长期的IDV光变与VLBI结构的演化。S4 0917+624是乌鲁木齐IDV监测项目的目标源之一，从2005年8月到2010年1月，利用南山25米射电望远镜在5GHz波段对该源进行了长达约4.5年的观测，积累了丰富的观测数据。在我们的观测中，类星体0917+624显示了熄灭的抑或有时非常弱的IDV，而在2000年前，该源是最显著的IDV源之一， 我们新的观测数据没有显示0917+624强的IDV。结合历史的IDV观测数据，我们考察了0917+624长期的IDV光变，结果表明，从2000年至今，0917+624强的IDV已经熄灭。利用MOJAVE 15.3GHz的观测数据，我们考察了类星体0917+624 长期的VLBI结构变化。通过高斯模型拟合，我们获得了该源VLBI核与内喷流成分的流量密度及去卷积的角尺寸，分析了VLBI核的流量密度、角尺寸、谱指数、亮温度等性质，同时研究了5GHz与15GHz之间光变的时间延迟。该射电源许多内喷流成分的出现能够部分消减其IDV，特别是成分C5、C6、C8和C9。2000年之后，类星体0917+624强的IDV的熄灭至今令人困惑且此强的IDV熄灭不能通过VLBI结构变化（角尺度增大）引起的IDV减弱 效应来解释，但很可能该源强IDV的消失是由于星际闪烁介质偏离了我们的观测视线引起的。未来多波段IDV及VLBI观测以及其它星际介质的观测将有助于研究引起S4 0917+624强IDV消失的星际介质的性质。 本论文相关研究工作得到国家自然科学基金的经费支持（资助项目号No.11073036，No. 11273050）。 |
| 英文摘要 | Blazar is an important subclass of active galactic nuclei (AGNs), which consist of flat-spectrum radio quasars and BL Lac objects. They are variable in almost whole electromagnetic spectrum from radio to gamma-ray. Very Long Baseline Interferomety (VLBI) achieved the highest angular resolution in drawing images of astronomical radio sources and it has made significant contribution to our understanding of AGNs. With the technique of VLBI, blazars can be resolved into a compact core and of ten one-sided jet components in parsec scale or sub-parsec scale. This dissertation focuses on the studies of variability of VLBI core of blazars. The following chapters are going to give an introduction to AGNs and variability studies of blazars and the application of VLBI to blazars studies. In Chapter 4, we present the results of correlations between the peak flux density and the position angle (PA) of inner-jet in 50 blazars at 15 GHz and three typical blazars S5 0716+714、S4 1807+698、[HB89] 1823+568 have been analyzed. Diverse correlations between the long-term peak flux density and the PA evolution of the major axis of the blazars core have been found in about 20% of the 50 sources. Based on the geometric beaming effect, we propose inner-jet models to explain diverse correlations. Further studies show that for a larger sample of 78 blazars, about 25% blazars showed significant linear correlations between the integrated flux density and the PA evolution of the major axis of the blazars core. We also report the changes of the long-term integrated flux density and the PA for subclass of blazars and find that the Fermi LAT-detected blazars have on an average higher position angle changes of cores than the non-LAT detected blazars, and that the LAT-detected ones are associated with more variable cores in flux density. we also investigated the possible physical periodicity in the radio light curves of 59 blazars with Power Spectral Density (PSD) method. The result revealed these radio blazars sources display a possible physically periodicity in a range of 2.6 to 11.1 years. Chapter 5 present the result of S4 0917+624 observed with Urumqi 25m telescope from August 2005 to January 2010. The quasar S4 0917+624 is one of the targets in the Urumqi flux density monitoring program at 4.8 GHz. The quasar S4 0917+624 exhibits only very weak or no IDV during our 4.5 year observing interval. Prior to year 2000, the source was one of the most prominent IDV sources. Our new data indicate that the previous significant IDV has ceased. We also analyzed the long term VLBI structural variability at 15 GHz using MOJAVE database. With the Gaussian model-fitting, we obtained the flux densities and the de-convoluted sizes of core and inner jet components of 0917+624. We studied the properties of angular size, spectral index, and brightness temperature of VLBI core for 0917+624, as well as the time delay between 5 and 15 GHz variations, and compared them with the IDV properties of 0917+624. The source shows ejection of several jet components that are suspect to have partially reduced the IDV amplitude of 0917+624. The vanishing of prominent IDV in S4 0917+624 after year 2000 is a mystery and cannot be explained via the quenching effect by changes in the observable VLBI structure. It however may be due to the interstellar scintillation medium has moved out of our line of sight or the properties of the interstellar scintillation medium have changed significantly. Further multi-frequency IDV and VLBI observations and other scintillation medium observations will help to study the properties of the interstellar medium which cause the quenching of the strong IDV for S4 0917+624. This work is supported by the National Natural Science Foundation of China (No.11073036, 11273050). |
| 学科主题 | 天体物理 |
| 语种 | 中文 |
| 源URL | [http://ir.xao.ac.cn/handle/45760611-7/646]  |
| 专题 | 研究生 新疆天文台_射电天文研究室 |
| 推荐引用方式 GB/T 7714 | 米立功. 耀变体VLBI核的光变研究[D]. 中国科学院新疆天文台. 中国科学院大学. 2015. |
入库方式： OAI收割
来源：新疆天文台
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