# Microlensing of the broad emission line region in the lensed quasar J1004+4112

## TL;DR

This study analyzes microlensing effects on the broad emission line region of the lensed quasar J1004+4112 over 15 years, constraining its size, geometry, and kinematics through spectral modeling.

## Contribution

It provides the first detailed modeling of microlensing-induced line profile distortions to infer the BLR structure and size in J1004+4112, favoring simple BLR geometries.

## Key findings

- The microlensing effect is consistent over 15 years, mainly magnifying the blue side of the line.
- The CIV BLR size is estimated at approximately 2.8 light-days, smaller than reverberation mapping predictions.
- Keplerian disk or equatorial wind models best reproduce the observed line distortions.

## Abstract

J1004+4112 is a lensed quasar for which the first broad emission line profile deformations due to microlensing were identified. Detailed interpretations of these features have nevertheless remained controversial. Based on 15 spectra obtained from 2003 to 2018, we revisit the microlensing effect that distorts the CIV broad emission line profile. We show that the microlensing-induced line profile distortions in image A, although variable, are remarkably similar over a period of 15 years. They are characterized by a strong magnification of the blue part of the line profile, a strong demagnification of the red part of the line profile, and a small-to-negligible demagnification of the line core. We used the microlensing effect to constrain the broad emission-line region (BLR) size, geometry, and kinematics. For this purpose, we modeled the deformation of the emission lines considering three simple, representative BLR models: a Keplerian disk, an equatorial wind, and a biconical polar wind, with various inclinations with respect to the line of sight. We find that the observed magnification profile of the CIV emission line can be reproduced with the simple BLR models we considered, without the need for more complex BLR features. The magnification appears dominated by the position of the BLR with respect to the caustic network -- and not by the velocity-dependent size of the BLR. The favored models for the CIV BLR are either the Keplerian disk or the equatorial wind, depending on the orientation of the BLR axis with respect to the caustic network. We also find that the polar wind model can be discarded. We measured the CIV BLR half-light radius as $r_{1/2} = 2.8^{+2.0}_{-1.7}$ light-days. This value is smaller than the BLR radius expected from the radius-luminosity relation derived from reverberation mapping, but it is still in reasonable agreement given the large uncertainties.