Variability Of QSOs Showing Broad Absorption Line Disappearance

BAL variance is common for Broad absorption line quasar (BAL QSOs). The disappearance of BAL troughs is expected to be a rare event. With the BAL QSOs sample with BAL disappearance found by Filiz Ak et al., in this thesis, we use the SDSS Survey Data to investigate their spectral variability. Chap1is the researching background, describing the basic features of active galactic nuclei (AGNs), BAL QSOs, as well as the recent research results on BAL QSOs and their BAL variability. Chapter2is our researching work. Chapter3is the conclusion and outlook.For these19BAL QSOs with CIV BAL disappearance (1.71<z<2.57), we use two-epoch spectra to investigate the relation between the BAL variance and the QSOs properties, such as the luminosity, spectral index. The time interval in the rest frame is1.1-3.9yr. The main results are summarized as follows:(1) There is no correlation between the EW variance and the flux variance. However, it is found that most of BAL QSOs become brighter with the disappearance of BAL trough.(2) There is no correlation between the EW variance and the spectral slope variance. There are about half BAL QSOs become bluer with the disappearance of BAL trough.(3) The timescale of C IV BAL disappear is about1000days.(4) For BAL QSOs with BAL disappearance, there are about half objects showing bluer spectra with the disappearance of BAL trough, which is consistent with the slope-variance result for high-z QSOs.