Transient C IV Broad Absorption Lines in radio detected QSOs

TL;DR

This study investigates transient C IV broad absorption lines in radio-detected quasars, finding a higher detection rate than previous studies and suggesting that these transients are likely part of BAL variability rather than driven by radio jets or continuum changes.

Contribution

It provides the first systematic analysis of transient C IV BALs in radio-detected QSOs, highlighting their properties and potential independence from QSO intrinsic parameters.

Findings

Transient C IV BALs are associated with high velocities and low equivalent widths.

Detection rate of transient BALs is higher than previously reported.

Transient phenomena are independent of QSO properties like Eddington ratio and black hole mass.

Abstract

We study the transient (i.e. emerging or disappearing) C IV broad absorption line (BAL) components in 50 radio detected QSOs using multi-epoch spectra available in Sloan Digital Sky Survey DR10. We report the detectionof 6 BALQSOs having at least one distinct transient C IV absorption component. Based on the structure function analysis of optical light curves, we suggest that the transient absorption is unlikely to be triggered by continuum variations. Transient absorption components usually have low C IV equivalent widths (< 8 \AA), high ejection velocities (> 10000 \kms) and typically occur over rest-frame timescales > 800 days. The detection rate of transient C IV absorption seen in our sample is higher than that reported in the literature. Using a control sample of QSOs, we show that this difference is most likely due to the longer monitoring time-scale of sources in our sample while the effect of small number statistics cannot be ignored. Thus, in order to establish the role played by radio jets in driving the BAL outflows, we need a larger sample of radio detected BALs monitored over more than 3 years in the QSO's rest frame. We also find that the transient phenomenon in radio detected and radio quiet BALs does not depend on any of the QSO properties i.e. the Eddington ratio, black hole mass, bolometric luminosity and optical-to-IR colours. All this suggests that transient BAL phenomenon is simply the extreme case of BAL variability.