2021ApJ...906L...8Z

We present an analysis of the variability of broad absorption lines (BALs) in a quasar SDSS J141955.26+522741.1 at z = 2.145 with 72 observations from the Sloan Digital Sky Survey Data Release 16 (SDSS DR16). The strong correlation between the equivalent widths of BALs and the continuum luminosity, reveals that the variation of BAL troughs is dominated by the photoionization. The photoionization model predicts that when the time interval ΔT between two observations is longer than the recombination timescale t_rec, the BAL variations can be detected. This can be characterized as a "sharp rise" in the detection rate of BAL variation at ΔT = t_rec. For the first time, we detect such a "sharp rise" signature in the detection rate of BAL variations. As a result, we propose that the t_rec can be obtained from the "sharp rise" of the detection rate of BAL variation. It is worth mentioning that the BAL variations are detected at the time intervals less than the t_rec for half an order of magnitude in two individual troughs. This result indicates that there may be multiple components with different t_rec but the same velocity in an individual trough.