Research On High-energy Radiation Of Blazar

Galaxies constitute an important unit of the universe and are important objects for studying the formation and evolution of the universe.A small fraction of galaxies(about 2%)exhibit activity,and their main physical features show rapid and obvious changes,called active galaxy(AG),and their central part is called active galactic nuclei(AGN),and no distinction is made between active galaxies and active galactic nuclei.Blazars are one of the most special subclasses of active galactic nuclei,with relativistic jets at small angles to the observer’s line of sight,and thus exhibit some extreme features,such as fast and large variability,high luminosity,high polarization,apparent superluminal motion,and high-energy gamma-ray emission.According to the intensity of the optical emission lines,the blazars are classified into two kinds of subclasses BL Lacertae objects(BL Lacs)and flat-spectrum radio quasars(FSRQs).Since the Fermi Large Field Telescope(Fermi/LAT)was launched,thousands of blazars have been discovered,and such a large sample is important for the origin of the extragalactic high-energy background and the high-energy emission of blazars.The spectral energy distribution of blazars usually have a two-hump structure.According to the leptonic model,the first low-energy peak is considered to be from the synchrotron radiation of relativistic electrons in the jet,and the second peak is from the inverse compton radiation,which can be divided into the External Compton process(EC;soft photons originate from outside the jet)and the synchronous self-Compton process(SSC;soft photons originate from the photon field generated by the synchrotron radiation of relativistic electrons in the jet)depending on the source of the soft photons.This academic Paper focuses on the high-energy radiation of blazars,specifically the composition of the high-energy radiation of blazars,the classification of Blazar Candidates of uncertain type(BCU),and the radiation mechanism of high-energy gamma rays.This academic Paper consists of three parts: the first part is the review part;the second part is the research part;and the third part is the conclusion and outlook.The study part includes: 1)classified the X-ray radiation into core and extended component and calculated X-ray the core dominance parameters to support the unification of BL objects with FRI/FRII(G)and FSRQ with FRII(Q);2)classified 1517 unclassified blazars using machine learning methods,and obtained 811 BL Lac object candidates and 397 FSRQ candidates;3)the spectral energy distribution of Mrk 421 was fitted to support that the high-energy gamma radiation comes from the SSC.the details are described in Chapters 2,3,and 4,as follows.In Chapter 2,the two-component model of the blazars in the high-energy band is studied with a large sample of X-ray sources.From the available literature,397 sources with luminosities containing X-ray,radio-band,and radio core dominance parameters are collected,and the X-ray core dominance parameters are calculated and the difference of X-ray core dominance parameters between the two types of blazars is discussed.In the two-component model model,the AGN emission is usually composed of two components,the core component and the extended component,which are generally discussed in the radio band.The results show that in the X-ray band,(1)the core component is dominant;(2)the average X-ray core dominance parameters of BL Lacs objects is larger than that of FSRQs;(3)the relationship between the spectral index and the core dominance parameters in the context of the unified model indicates that FRIs/FRII(G)s and BL Lac objects belong to the same class of objects,and FRII(Q)s and FSRQs belong to the same class of objects.In Chapter 3,a machine learning algorithm is used to classify BCUs.There are a large number of blazars detected by the Fermi telescope that are identified as BCUs because of their low spectral quality or lack of spectral information,and the classification of these BCUs is important for studying the nature of high-energy radiation from blazars.In this work,1517 BCUs in the Fermi Point Source CatalogData Release 3(4FGL-DR3)were classified using five algorithms: k-nearest neighbor,logistic regression,support vector machine,random forest,and Cat Boost,and the classification results were identified as successful if the results of the five algorithms were consistent,and the results of unknow were maintained if the five models were not consistent.Finally,we obtained 811 BL Lacs candidates,397 FSRQs candidates,and 309 remain the unknow result.In Chapter 4,a multi-wavelength spectral energy distribution analysis(SEDs)of Mrk421,the Major Atmospheric Gamma Imaging Cherenkov telescope(MAGIC),has published observations in the high-energy band during December 2016 and June 2017 data.In this work,the energy spectrum for this period is analyzed with the SED,and the results show that the spectrum can be reproduced with a One-zone synchrotron self-Compton model,and that the Tev emission results from the inverse Compton scattering of the synchrotron photon field produced by relativistic electrons in the jet.With the increase of high-energy telescopes in space and the improvement of ground-based high-energy experiments,we will have a deeper understanding of the extreme relativistic physics in blazer’s jet,which will help us better understand the high-energy radiation from blazars.