Analysis On The Variability Of Blazars

Active Galactic Nuclei(AGNs)are the frontiers of modern astrophysics research,and it is of great significant to study the properties of supermassive black holes.Blazars are a special class of AGNs.The most prominent feature of these objects is their rapid and intense variability.The study of variability is an important means to understand the internal structure of Blazars and the properties of the black holes in these objects.According to the different time scales,variability can be divided into three categories: intra-day variability(micro-variability),short-term variability and long-term variability.A large number of observations have found that the variability of Blazars has periodic variability under different time scales.The study of the period is a useful tool to explain the causes of variability in Blazars and to understand the internal structure of AGNs.In this thesis,we studied the periodic variability of Blazars.The paper consists of four chapters.In the first chapter,the basic properties and classification of active galactic nucleis and their important components are introduced.In the second chapter,we introduced the variability characteristics of Blazars and the binary black hole model,the precession jet model and the helical jet model.In chapter 3 we introduced several methods for analyzing variability period.These methods include Jurkevich method,continuous wavelet transform and weighted wavelet Z transform.The application of these methods is illustrated by some examples.Jurkevich method and weighted wavelet Z-transform are both suitable for non-uniform sampling data processing,while continuous wavelet transform needs to interpolate the data.In the 4th chapter,three Blazars are selected and their historical light curve is analyzed.OJ 287 is one of the most widely studied Blazars,its unique long-term historical observations make it a typical example in the study of periodic variability.Many studies have found that there are two supermassive black holes in this object.The two black holes interact with each other during rotation process,and generate a12-year periodic variability.In addition to this period,there are other quasi-periodic variability on its light curve.We compiled the latest 40-year variability data and analyzed these data using Jurkevich method and weighted wavelet Z-transform,and found a 430-day period.We also analyzed the variability data of 3C 66 A and BL Lac0716+714 in the optical V band,and found stable periods of 6.1-year and 3.2-year in3 C 66A,and a quasi-period of 1000 day in 0716+714.