The Study On The Jet In Radio Galaxy

Active galatic nuclei(AGNs)are powered by gravitational energy released by accreting matter of the central supermassive black holes,theirs nuclei have extremely special physical environment,which can produce violent activities and multi-band variabilities.About ten percent AGNs have relativisitic jets.However,the jet physics of AGNs is much unclear,such as the jet formation,acceleration,collimation,energy dissapition and jet contents.Based on radio galaxy,this thsis will study the accretion process and the jet formation around the black hole,the jet energy dissipation on pc sacle and jet physics on kpc scale.In chapter 1,we briefly introduce the AGNs,which include the accretion process of the black hole and jet physics and their recent progress.In chapter 2,we study the accretion and jet formation process,based on a special radio galaxy,Hercules A(HerA).HerA has a several hundred kpc scale jet with strong low frequency radiation,but its core is very weak,quickly,we reduce and analyze the radio data of HerA that observed by the Expanded Very Large Array(EVLA)during 2010-2011 at C band.We find the spectrum of both lobe and core are very steep.Futher more,the core flux becomes weaker for about ten percent compared with that in twenty years ago,which suggest that the central engine is still dying quickly.We also find Her A deviates a lot from the relation between[O ?]luminosity and low frequency 178 MHz luminosity(L_{[O ?]}-L_178MHz)as defined by other FR ?/? sources(FR ?/?,Fanaro-Riley type ?/?).However,when only radio core emission is considered,it roughly follows the L_{[O ?]}-L_178MHz correlation.This indicates the accretion and jet may be not involed simmultaneously.Finally,we fit the core spectrum and jet power,based on a radiatively inefficient accretion flow and jet model around a rotating black hole with the estimated Bondi accretion rate from the X-ray observation.The large scale jet production should need much higher accretion rate.In chapter 3,we estimate the position of the main energy dissipation region of the jet,combining the fitting of the spectral energy distributions(SEDs)and the core-shift effect.We model simultaneous or quasi-simultaneous SEDs for a sample of 25 blazars that have radio core-shift measurements based on the one-zone leptonic model combined with Markov chain Monte Carlo technique.In the Compton scatter process,we consider the SSC(Synchrontron self-Comptom)and EC(external Comptom)process.The seed photons from the broad line region(BLR)and molecular torus are considered respectively in the EC process.In most of the source,we find the SEDs ftting with the seed photons from the torus are better than those from BLR,which suggests that,in our blazars sample,the?-ray emitting region in the jet may be located outside of BLR.Assuming the magnetic field strength in the?-ray emitting region as constrained from the SED ftting follows the magnetic field distribution as derived from the radio core-shift measurements,we further calculate the location of the?-ray emitting region in the jet,R_Y,for these blazars.We find that the mean value of R_Y?2×10⁴R _S or 10R_BLR(R_S is the Schwarzschild radius andR_BLRis the BLR size),which is consistent with the SED fitting results.In chapter 4,we study the magnetic field in kpc-Mpc scale jet,based on the analysis of six FR ? radio galaxies and comparision with the simulations.We analyze the EVLA data of six nearby FR ?s.We find,at the lobe edge,Cygnus A(Cyg A)and Her A show properties of intensity distribution with quiet smooth edge and sharply decreasing,higher fractional polarization and the magnetic field direction along the lobe edge.For two dimensional slices,they show higher variability in polarization intensity compared with intensity,smooth change of the polarization angle with the varing range close to 180 degrees and high mean fractional polarization.Those properties are consistent with the simulation of magnetic tower model simulations,which indicate the magnetic field may be important in their large scale jet lobe system.3C 424 globally showes properties of diffuse structure,irregular magnetic field direction at the lobe edge.For two dimensional slices,they show scatter distribution and small varing range of the polarization angle and low mean fractional polarization.These are similar with the results of hydrodynamic model,which may indicate the magnetic field is not important in its jet lobe system.Other three sources are similar with the magnetic tower model reults in global map,however,we can not get strong conclusion due to the insufficient resolution.In chapter 5,we give a brief summary on this thesis,and present the prospects of the possible future work on this topic.