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

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).

A sharp rise in the detection rate of broad absorption line variations in a quasar SDSS J141955.26+522741.1

“…In the opposite case, there will be a negative correlation. Same as reported by Hemler et al (2019) and Lu & Lin (2019), there are strong negative correlations between the BAL EW and the continuum luminosity at 1500Å for all the three regions (see Figure 2). The correlation coefficients and p-values are marked in Figure 2.…”

“…This object has 72 observations with the signal-tonoise ratio (S/N) level at g band greater than 5 in all the epochs. This object was found to have a strong correlation between the BAL trough and the continuum flux by previous studies (e.g., Hemler et al 2019;Lu & Lin 2019). The strong correlation and multiple observations make this object an ideal laboratory for the BAL studies.…”

“…It is well known that the BAL troughs are able to vary over timescales from days to years (Capellupo et al 2011(Capellupo et al , 2012Filiz Ak et al 2012;Arav et al 2013;Filiz Ak et al 2013;He et al 2014He et al , 2015He et al , 2017Grier et al 2015;Hemler et al Corresponding author: Zhicheng He, Guilin Liu zcho@ustc.edu.cn, glliu@ustc.edu.cn 2019; Zhang et al 2015;Shi et al 2017;Sun et al 2017;Lu & Lin 2019). Two main mechanisms lead to BAL variations: (1) changes in the ionization of gas; and (2) absorbing gas moving in and out of the line of sight.…”

A Kinematic Shift of the C iv Broad Absorption Line in Quasar SDSS J120819.29+035559.4

“…Second, the continuum flux of the source shows obvious weakening. Correlations between the variations of the ionizing continuum and those of outflow absorption lines have already been proved (Lu et al 2017;Chen et al 2018a,b, 2019Lu et al 2018;Lu & Lin 2018c, 2019Huang et al 2019;Vivek 2019 for BALs), which could, at least to some extent, be served as an evidence for supporting the IC scenario as the main origin of absorption line variability. For J1208+0355, along with strengthenings of the absorption lines, the power-law continuum (the purple and blue smooth curves in Figure 1) in the second epoch is on average 41% lower than in the first epoch.…”

“…Line-locking signature in NALs has been generally identified from both BAL and non-BAL quasars (e.g., Foltz et al 1987;Srianand et al 2002;Hamann et al 2011;Bowler et al 2014). Lu & Lin (2018b) represented the report of the line-locking phenomenon of blended NALs within trough-like BALs in quasar SDSS J021740.96-085447.9. In J1208+0355, we once again found Line-locking signature of the blended NALs within a BAL (system B, see Table 2), which supports the idea that these outflow clouds are driven by radiative force caused by resonance lines.…”