Microlensing and Intrinsic Variability of the Broad Emission Lines of Lensed Quasars

TL;DR

This study investigates the effects of microlensing and intrinsic variability on broad emission lines in lensed quasars, revealing two distinct broad-line region regions and implications for quasar accretion disk structure.

Contribution

It identifies two separate regions in the broad-line region with different microlensing sensitivities, advancing understanding of quasar structure and microlensing effects.

Findings

CIV shows strong microlensing in some cases.

Good match between the red wings of CIV and CIII] profiles when microlensing is weak.

Evidence for two BLR regions with different sizes and kinematic properties.

Abstract

We study the BELs in a sample of 11 gravitationally lensed quasars with at least two epochs of observation to identify intrinsic variability and to disentangle it from microlensing. To improve our statistical significance we also include 15 systems with single-epoch spectra. MgII and CIII] emission lines are only weakly affected by microlensing, but CIV shows strong microlensing in some cases, even for regions of the line core, associated with small projected velocities. However, excluding the strongly microlensed cases, there is a strikingly good match between the red wings of the CIV and CIII] profiles. Analysis of these results supports the existence of two regions in the BLR, one that is insensitive to microlensing (of size $\gtrsim$ 50 light-days and kinematics not confined to a plane) and another that shows up only when it is magnified by microlensing (of size of a few light-days, comparable to the accretion disk). Both regions can contribute in different proportions to the emission lines of different species and, within each line profile, to different velocity bins, all of which complicates detailed studies of the BLR based on microlensing size estimates. The strength of the microlensing indicates that some spectral features that make up the pseudo-continuum, such as the shelf-like feature at {\lambda}1610 or several FeIII blends, may in part arise from an inner region of the accretion disk. In the case of FeII, microlensing is strong in some blends but not in others. This opens up interesting possibilities to study quasar accretion disk kinematics.