Multi-wavelength Study Of Blazar Light Variability And Broad Band Spectrum

The active galactic nucleus（AGN）is one of the most active celestial bodies in the universe.It is located in the central region of a special type of extragalactic galaxy,where a supermassive black hole accretes surrounding matter and produces electromagnetic radiation mainly covering the whole band of non-thermal radiation..Blazars are a very special subclass of active galactic nuclei.The relativistic jets of blazars point to our earth.They are very bright gamma-ray sources that can be observed in a wide range of energies.Blazars Jets accelerate electrons,protons and nuclei to very high energies.Blazars are predominantly radio-noisy active galactic nuclei whose radiating core is dominated by.Blazars have large and rapid light changes,and obvious polarization phenomena have been detected in the radio and optical bands,and both the polarization angle and the polarization amplitude are changing.The energy spectrum mainly presents the form of non-thermal continuum,and it is also the most extensively studied active galactic nuclear observation.The first chapter of this paper gives a brief overview of active galactic nuclei,and we introduce the research history,basic characteristics,classification and unified model of active galactic nuclei.The second chapter mainly introduces the observation characteristics,classification,multi-band characteristics and physical interpretation of blazars and the sequence of blazars.The third chapter of this paper mainly explains the radiation process of blazars.We simply deduce the black body radiation process,synchrotron radiation process and inverse Compton scattering process.Secondly,further describe the very important lepton model in the blazar radiation process.In the fourth chapter,we classify the two subtypes of blazars based on the support vector machine algorithm of machine learning.There are two obvious peaks in the spectral energy distribution（SED）of the blazar,of which the low energy peak is the synchrotron radiation peak.There is an inverse correlation between the peak power of the synchrotron radiation peak of the blazar and the peak frequency,so the spectral index plane constructed by the multi-band composite spectral index related to the SED peak can be used as a classifier for the two subclasses of the blazar（flat-spectrum radio quasar（FSRQ）and BL-Lac object）.In this paper,the cross matching of multi-wavelength data for the blazars in the Fermi four Catalogue（4FGL-DR3）is carried out through the database of Strasbourg Observatory,and multi-wavelength data set are obtained.Basing on this data set,we find that the distributions of the 8 broad band spectral indices,(α_rw1、α_rw2、α_rw3、α_ro、α_rγ、α_w1w2、α_w1w3)andα_w3x,have obvious bimodal structure,and clearly distinguish the two subclasses of blazed variants（FSRQ and BL Lac）.Through the support vector machine model in machine learning technology,we further analyzed the classification effect of spectral index plane on subclasses of blazar,and find that most of the accuracy rates are above 80%.In Chapter 5 we study the flare behavior of the bright gamma-ray FSRQ4C+31.03,collecting about 15 years of Fermi-LAT data from August 2008 to February2023.A bright period of gamma-ray activity was identified,which was also the brightest ever seen in this source by Fermi satellite observations.We observe that the main peaks of the gamma-ray flares are essentially symmetrical in profile.This gamma-ray spectrum is fitted with PL and LP spectral models,in both cases the spectrum during the flare is stiffer than that at rest.Thisγ-ray spectrum extends beyond energies of 10 Ge V,suggesting that not only emission is generated within the BLR.Multi-band research shows that there is an obvious correlation betweenγ-rays,X-bands,and optical ultraviolet bands,which indicates that multi-band radiation comes from the same region.We then modeled the broadband SED with a simple single-sector radiation model using the public code"JETSET".From the spectral modeling of different states in broadband,we found that the main blaze state Flare-1A seed photons mainly originate from the accretion disk and the broad line region,while the subblaze state Flare-1B seed photons mainly originate from the broad line region and dust ring,the quiet static seed photon mainly comes from the dust ring.