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Blazar的γ射线光变特征及其与射电光变的相关性
其他题名Gamma-ray Variability of Blazars and its Correlation with Radio Variability
王钧陶
学位类型硕士
导师白金明
2014-04-01
学位授予单位中国科学院研究生院(云南天文台)
学位授予地点北京
学位专业天体物理
关键词活动星系 耀变体 4c 21.35 伽马射线 射电 光变
摘要活动星系核是一类中央核区活动性很强的河外星系的核心。当射电噪的活动星系核的相对论性喷流指向我们观测者时(通常与视线夹角≤10),在观测上形成一类特殊的活动星系,被称为Blazar。Blazar通常表现出极强的视光度(可达1049erg s1)、非热辐射主导(从射电到γ射线)、整个电磁波段不规则和快速的光变、射电和光学波段的高偏振和射电子成分的视超光速运动。因为Blazar的辐射主要来源于相对论性的喷流,因此Blazar成为研究喷流极高能天体物理的天然实验室。此外,对Blazar的研究可以促进我们对AGN中心引擎黑洞、大尺度磁场的形成和河外γ射线背景等的认识。尽管前人已经对Blazar进行了全方位的研究并且对其本质有了深入的了解,但至今仍然存在着许多未解决的问题(比如说,相对论性喷流的成分和形成机制、SED高能成分的辐射机制和γ射线辐射区的位置等)。 光变的研究(包括光变时标、光变曲线随时间的变化、光变过程中谱形的改变和多波段光变的相关性等)则可能揭示出辐射区的位置,辐射区内部物理条件和结构的变化,也可能揭示辐射过程和机制的改变,所以对γ射线的光变研究变得极其重要。VLBI(very-long-baseline interferometry)观测是目前唯一能够在毫角秒尺度上分辨Blazar喷流的观测手段,因此同时研究γ射线与射电波段的相关性有助于确定γ射线辐射区的位置。特别是γ射线与射电子源的喷出或与射电光变的相关已在多个Blazar中被发现,例如OJ287、PKS1510-089、Mrk421、3C454.3等。但是前人的研究结果也存在着矛盾的地方,比如说在γ射线与射电谁领先的问题上,因此需要进一步的分析与研究。 全文共分三章。第一章介绍活动星系核的历史背景、特征、分类、模型和辐射机制。第二章介绍γ射线的观测设备、Blazars γ射线的辐射特征和γ射线与射电辐射的相关性。第三章着重介绍4C21.35的γ射线光变特征及其与射电光变的相关性。我们利用从2008年8月5日到2013年10月23日Fermi-LAT的观测数据,对4C21.35的100MeV到300GeV的γ射线数据进行了分析,总结了1天bin情况下的光变特征,并在3小时bin的基础上详细研究了所选的11个大的爆发,得到了5.4小时的最短光变时标。还利用对射电光变曲线减去一个线性增长的方法,通过相关分析得到100MeV <300GeV的γ射线光变领先于15GHz射电光变359.3+81.05.8天,并用γ射线辐射区对于射电辐射是光学厚对其加以解释,从而在辐射区匀速运动的假设下得到这样的时延对应着γ射线辐射区到射电光学薄区域的距离为r≈45.2pc。继而通过与VLBA观测得到的15GHz射电核的半径相比较,得到辐射区向外运动过程中可能存在着减速。
其他摘要Active Galactic Nuclei(AGNs) are the strongly active centers of one particular kind of galaxies. When the relativisitic jets of raido-loud AGNs point close to us, there will form a special kind of AGNs which is called Blazars. Blazars often exhibit huge apprent luminosities, non-thermal emission dominance, irregular and rapid variable emission in entire electromagnetic band, strong radio and optical polarization and superluminal motion. Since the emission from Blazars mainly comes from the relativistic jets, they become the excellent lobarotories for studying high-energy physics. In addition, the study of Blazars can also promote our understanding of the black hole, magnetic field on large scale, extragalactic Gamma-ray background, etc. Even though Blazars have been well studied at multiple wavelengths and much insight has been gained into the nature of these extreme objects, there are still numerous open issues remaining, such as the composition and formation of relativistic jets, the radiative mechanism of the high-energy part of the SED, the location of Gamma-ray emission region, etc. Variability studies, including the studies of variability time scale, light curve variation, spectra changes and multiwavelength correlation, could reveal the location of the emission region, the changes in the condition and structure in the emission region and the changes in the radiative processes and mechanisms, so it is essential to research the Gamma-ray variability. VLBI is the unique method to resolve Blazars on pc scale, thus the combination of Gamma-ray and radio studies would promote the localization of the Gamma-ray emission region. Particularly, the connections between Gamma-ray flares and the ejections of radio components have been found in a number of Blazars, for example, OJ 287, PKS 1510-089, Mrk421, 3C 454.3, etc. However, there are also contradictions in previous studies, such as whether Gamma-ray or radio leads, so further analyses and research are required. There are three chapters in this thesis altoghther. Chapter one is an overview of basic AGN knowledge, such as historical background, properties, categories, model and radiative mechanism. The chapter two introduces Gamma-ray instrumentation, the properties of Gamma-ray from Blazars and the Gamma-radio connection. In chapter three we emphasis the Gamma-ray variability of 4C 21.35 and its correlation with the radio variability. The Fermi-LAT data from 5 August 2008 to 23 October 2013 has been used to investigate the Gamma-ray properties of 4C 21.35 between 100 MeV and 300 GeV. Specifically, the variability properties with 1-day time bins have been summaried, and 11 chosen marked bursts have been analysed in detail with 3-hour time bins. The shortest variability time scale we have got is 5.4 hours. We also use the method of subtracting a linear increase from the original radio light curve, and then by correlation analysis conclude that the Gamma-ray variations lead the 15 GHz radio variations by about 359.3 days. The radio opacity in the Gamma-ray emission region is used to interpret the delay, and the distance between the Gamma-ray emission region and the region becoming transparent in radio band of about 45.2 pc has been obtained provided that the emission region is in uniform motion. Then by comparing it with the radio core radius obtained by VLBA, a decelarating inner jet is likely to exist.
学科领域天文学
页数66
语种中文
文献类型学位论文
条目标识符http://ir.ynao.ac.cn/handle/114a53/5568
专题丽江天文观测站(南方基地)
推荐引用方式
GB/T 7714
王钧陶. Blazar的γ射线光变特征及其与射电光变的相关性[D]. 北京. 中国科学院研究生院(云南天文台),2014.
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