| 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. |
修改评论