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

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