# Evidence for photoionization-driven variability in narrow absorption lines

## TL;DR

This study finds a strong link between narrow absorption line variability and ionizing continuum changes in quasars, suggesting different gas sensitivities and continuum fluctuations as key factors.

## Contribution

It provides evidence that NAL variability is driven by ionizing continuum fluctuations, revealing two types of absorbing gas with different sensitivities.

## Key findings

- NAL variability correlates with continuum changes
- Two subsamples show opposite correlation patterns
- Ionizing continuum fluctuations cause NAL emergence or disappearance

## Abstract

In this Letter, we report the discovery of a strong correlation between the variability of narrow absorption lines (NALs) and the ionizing continuum from a two-epoch spectra sample of 40 quasars containing 52 variable C iv {\lambda}{\lambda}1548; 1551 absorption doublets. According to the concordance index, this sample is classified into two subsamples. Subsample I shows an anti-correlation between the variations of absorption lines and the continuum, while Subsample II exhibits a positive correlation. These results imply that these variable C iv {\lambda}{\lambda}1548; 1551 absorption doublets are intrinsic to the corresponding quasars and that their variations are caused primarily by the fluctuations of the ionizing continuum. Based on our analysis, we propose that there might be two kinds of absorption gas: one that is very sensitive to the continuum variations, the another that is not. In addition, we suggest that in many cases the emergence or disappearance of NALs is caused by fluctuations of the ionizing continuum.