Variability of QSOs with variable regions in broad absorption troughs from the Sloan Digital Sky Survey

TL;DR

This study analyzes the variability of broad absorption lines in 188 BAL quasars from SDSS DR7 over 0.001 to 3 years, revealing correlations with accretion processes and black hole properties.

Contribution

It provides new insights into the variability patterns of BAL regions and their connection to central accretion activity in quasars.

Findings

Variable regions are more common over longer time intervals.

Variable regions tend to be narrower than outflow velocities.

BAL variability correlates with continuum luminosity and accretion parameters.

Abstract

The variability of broad absorption lines is investigated for a sample of 188 broad-absorption-line (BAL) quasars (QSOs) ($z > 1.7$) with at least two-epoch observations from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), covering a time-scale of about 0.001 -- 3 years in the rest frame. Considering only the longest time-scale between epochs for each QSO, 73 variable regions in the \civ BAL troughs are detected for 43 BAL QSOs. The proportion of BAL QSOs showing variable regions increases with longer time-interval than about 1 year in the rest frame. The velocity width of variable regions is narrow compared to the BAL-trough outflow velocity. For 43 BAL QSOs with variable regions, it is found that there is a medium strong correlation between the variation of the continuum luminosity at 1500 \AA\ and the variation of the spectral index. With respect to the total 188 QSOs, larger proportion of BAL QSOs with variable regions appears bluer during their brighter phases, which implies that the origin of BAL variable regions is related to the central accretion process. For 43 BAL QSOs with variable regions, it is possible that there is a negative medium strong correlation between the absolute variation of the equivalent width and the \mgii-based black hole mass, and a medium strong correlation between the maximum outflow velocity of variable regions and the Eddington ratio. These results imply the connection between the BAL-trough variation and the central accretion process.