Study On X-ray Spectral Evolution In Black Hole Binaries And Changing-look Active Galatic Nuclei

As one of the most important process in cosmos,the activity of black hole(BH)and its related high-energy objects are hot research field in astrophysics.Based on the BH masses,it can be classified into stellar-mass BH(3-20M_?)as BH X-ray binary(XRB)and supermassive BH(10^6-10M_?)as active galactic nucleus(AGN).Since accretion is the central engine for BH activities,we can understand the physical properties of BH XRB and AGN by researching this process.Originating from the inner region of BH system,X-ray spectrum which reflect high energy properties of accretion,is thought as key method to study the evolution of accretion in BH.With decades of research,we acquired many knowledge of BH XRB and different types of AGNs.However,there are still many open issues in this field.For example,how does a XRB transit between different states and what drives the process?How do different types of galaxies evolve?How does the corona in the BH system form,and what is the relation between corona and accretion disk?In this thesis,we investigate the possible physical mechanisms for the evolution of XRBs and for the AGNs.This thesis is organized as follows.Chapter 1 firstly introduce the observational properties of different scale of BH systems(e.g.,XRB,AGN etc.).Then,we introduce the different types of accretion theories that are widely accepted in explaining the activities of the BH systems.At last,we introduce outflow in BH sources(e.g.,wind,jet).In Chapter 2,we present the X-ray spectral evolution for XRBs in whole outburst that including both rise and decay phases.In previous works,only the X-ray spectral evolution in decay phase was explored.We analyze RXTE data of 4 XRBs taken the rise and decay phases of 8 outbursts.We perform a systematic study for the evolution of X-ray spectral index,the X-ray flux and Eddington ratio.We find that in the initial rise phase,the X-ray spectral index is anti-correlated with the X-ray flux,and that as the X-ray flux reaching to the peak value,the spectrum quickly softens.In the decay phase,the X-ray photon index and the flux follow two different positive correlations.Then,after the X-ray flux is dropped below a critical value,the anti-correlation that is found in the rise phase is observed.In Chapter 3,we explore the spectral evolution of the X-ray emission from NGC1365,which is the X-ray CL AGNs that showed a strong variation of the column densities in the X-ray data.We analyze the X-ray data of NGC 1365 taken by XMM-Newton and Nu STAR,and find that the X-ray spectrum quickly softens as the X-ray luminosity increases,and the optical-to-X-ray spectral index increases as increasing of the optical luminosity.These results suggest that the intrinsic luminosities of both X-ray and optical emission are changed simultaneously,and the change of column density is not caused by the cloud moving in or moving out from our line of sight.The strong spectral evolution of NGC 1365 is quite similar to that found in optically CL AGNs with reappearance/disappearance of broad emission lines.These results support the hypothesis that the X-ray CL AGN also undergoes state transition,and the variation of column density may be caused by the variable disk winds during the strong evolution of the disk/corona.In Chapter 4,we further explore the X-ray properties for a larger sample of CL AGNs,which include both X-ray CL AGNs and optical CL AGNs.We find that photon index?and _{2-10ke V Edd}follows an anti-(or positive)correlation when _{2-10ke V Edd}is lower(or higher)than a critical value of?10^-3.This X-ray spectral evolution is consistent with the prediction of the accretion-mode transition.According to X-ray and optical spectrum observations performed quasi-simultaneously within one year,we find that the CL AGNs with and without broad emission lines stay in the positive and negative part of the?-_{2-10ke V Edd}correlation,respectively.Our results suggest that the change of the accretion mode is the physical reason for both the optical and X-ray CL AGNs.In Chapter 5,we investigate the statistical properties for a larger sample of CL AGNs that reported before January,2021.In total,we analyze 162 CL AGNs,which include 144optical CL AGNs and 18 X-ray CL AGNs.We present the BH mass,X-ray and/or optical luminosities,X-ray spectral index for those CL AGNs.We also search the radio emission in data taken by FIRST survey.We find the BH mass are in the range of?10^7-9M_?,which is the typical mass of AGNs.The bolometric Eddington ratio _{bol Edd}is in the range of?10^-3-10^-1(the average value?10^-2),which is lower than quasars(0.1-1)and higher than low-luminosity AGNs(_{bol Edd}?10^-6-10^-2).Therefore,CL AGN may correspond to the transition between ADAF-dominant stage and SSD-dominant stage.We do not find significant difference in distribution of BH mass,_{bol Edd},X-ray photon index between optical CL AGN and X-ray CL AGN.We conclude that(i)the variation of the hydrogen column density may be caused by disk winds during the evolution of disk;and(ii)the difference between optical and X-ray CL AGN may due to their different viewing angles,for which the optical CL AGN and X-ray CL AGN are observed at a smaller and larger viewing angles,respectively.In Chapter 6,we sumarize our main results,and disscuss the possible directions for our future work.