# Correlations between the Variation of the Ionizing Continuum and Broad Absorption Lines in Individual Quasars

## TL;DR

This study finds strong correlations between ionizing continuum variations and broad absorption line changes in quasars, indicating ionization fluctuations drive BAL variability on short timescales, with saturation effects observed.

## Contribution

It provides the first detailed statistical analysis linking ionizing continuum fluctuations to BAL variability in individual quasars using multi-epoch SDSS data.

## Key findings

- Significant correlations (>99%) between continuum and BAL variations in 21 quasars.
- BAL variability can occur on timescales as short as a few days.
- Si IV shows larger variation amplitudes than C IV, indicating saturation effects.

## Abstract

We discover the significant (significance level of >99%) correlations between the fractional variation of the ionizing continuum and that of the C IV and/or Si IV BALs in each of 21 BAL quasars that have at least five-epoch observations from the Sloan Digital Sky Survey-I/II/III. This result reveals that the fluctuation of the ionizing continuum is the driver of most of these BAL variations. Among them, 17 show negative correlations and the other 4 positive correlations, which agrees with the prediction of photoionization models that absorption line variability response to ionization changes is not monotonic. 8 quasars out of 21 examples have been observed at least 30 times on rest-frame timescales as short as a few days, which reveals that changes in the incident ionizing continuum can cause BAL variability even in such a short period of time. In addition, we find that most of the 21 quasars show larger variation amplitude in Si IV than C IV, which reveals the ubiquity of saturation in these BALs (at least for C IV BALs).