The Variability Symmetry Observational And Numerical Simulation Of Spectral Indexes Research Of Radio-loud AGN

Active galactic nucleus(AGN)is a kind of extragalactic galaxy with strong activity in the central region,which has strong variability and obvious spectrum evolution characteristics.Radio-loud AGN is one type of AGN,about 10 percent of all AGNs,with remarkable jet activity,its research has been one of the most active fields in AGN study.Radio-loud AGN include Radio galaxy,Blazar and Radio-loud Quasar,the variability of emission of radio-loud AGN arise from the physical mechanism of relativistic flows of plasma along jets.The numerical simulation of the relativistic jet of radio-loud AGN and the analysis of variability properties of Blazar,which is conducive to a deeper understanding of the physical factors affecting the shape distribution of the jet and the physical mechanism inside the jet,and it is of great scientific significance to understand the physical mechanism and structure of active galactic nuclei and their jets.Although the study on simulations of jets for extragalactic radio sources is now extensive,mainly on two dimensional relativistic jet,such morphologic sim-ulation of three dimensional relativistic jet,computations of light curves and the resulting power spectra produced by the jet motions are exceedingly rare.In the first half part of this thesis,we simulated the morphology of three-dimensional propagating relativistic jet of Radio-loud AGN and the spectral index of PSD.We used the Athena hydrodynamics code to simulate an extensive suite of 54 propagating three-dimensional relativistic jets with input jet velocities(vj)and jet-to-ambient matter density ratios(?).We determined which parameter sets yield unstable jets that prcoduce jet dominate FR ? type radio galaxy morpholo-gies and which tend to produce stable jets with hot-spots and FR ? morphologies.Higher velocity and density jets are much more powerful and stable,yielding FR? morphologies to large distances.We focused on simuluations that remain stable for extended distances(60?240)times the initial jet radius.Scaled to the much smaller sizes probed by VLBI observations,the fluctuations in such simulated flows yield variability in observed emissivity on timescales from months.Adopt-ing results for the densities,pressures and velocities from these simulations we estimated the light curves of emission,and finded that these simulations produce light curves that are reminiscent of those of many blazars.in terms of having both active and quiescent periods.We also studied the PSD properties of emis-sion light curves,with red-noise slopes between-2.1 and-2.5.so produced are similar to those observed from AG Ns.Blazar is a type of Radio-loud AGN with the jets nearly aligning to the observer's line of sight,it has rapid and large amplitude of flux variability across the complete electromagnetic spectrum.The variability properties include vari-ability timesc ales,polarization of variability,variability symmetry,the change of spectral shape in the process of variability,and the correlation of variability in different bands,and so on.The previous statistical research of variability symme-try are about quasars and Seyfert galaxies.However,the properties of spectrum and energy release for blazars may be different from quasars,with stronger and faster variability than optical quasars,may have different symmetric properties.The statistical research on a single source with well sampled observational data is important to investigate the origin of variation in blazar jets and constrain the physical models of blazars variability.In the following sections of this thesis,we investigated the variability symmetry properties of S5 0716+714 and W2R 1926+42.We investigated the possibility that the Blazar light curve was dom-inated by a large number of individual flares and adopted exponential rise and decay models to investigate the symmetry properties of flares.The results showed that,both S5 0716+714 and W2R 1926+42 were predominantly asymmetric with werk tendencies toward positive asymmetry(rapid rise and slow decay).The flare asymmetry was difficult to explain only by a light travel time effect but may be caused by differences between the timescales for acceleration and dissipation ofhigh-energy particles in the relativistic jet.The durations and the amplitudes of flares can be fit with log-normal distributions,which can be interpreted using minijet-in-a-jet model.Base on the parameters of simulation,we had estimated the emission region in the jet of Blazar.For S5 0716+714,the estimated sizes of pemission region are 2.4 × 1016?3.3 × 1018cm and 6.6 × 1014?4.8 × 1016cm.for STV and IDV.respectively.For W2R 1926+42.the sizes of the emission regions are estimated to be in the range of 1.1 × 1015?6.6 × 1016cm.Lomb-Scargle periodograms were used to estimate the power spectral density(PSD)shape of W2R 1926+42,it was well described by a power law with a median index-1.44.