2024RAA....24i5008Q

We investigate the relationship between the variability of broad absorption lines (BALs) or narrow absorption lines (NALs) and that of continuum using a data set of two-epoch SDSS spectra containing 134 C IV NAL-BAL pairs. Our analysis reveals an anti-correlation between the fractional equivalent width (EW) variations in NALs (or BALs) and the fractional flux variations of the continuum, with Spearman rank correlation coefficients of r = -0.47 (p = 1E-08) and r = -0.58 (p = 1E-13), respectively. In addition, we find a positive correlation between the fractional EW variations in NALs and BALs (r = 0.72, p = 1E-22), and derive a regression equation ΔEW_NAL/〈EW_NAL〉 = 0.803ΔEW_BAL/〈EW_BAL〉 + 0.008, with an intrinsic scatter of 0.14. These results suggest that the variability in the ionizing continuum may play a significant role in the observed changes in C IV NALs and BALs, supporting the idea of photoionization-driven variability. The co-variability between C IV NALs and BALs may imply that they originate from outflows with similar physical conditions.