Origin of Chromatic Features in Multiple Quasars -Variability, Dust, or Microlensing -

TL;DR

This study investigates the origins of color differences in lensed quasars, concluding that quasar microlensing and dust extinction, rather than intrinsic variability, best explain the observed chromatic features.

Contribution

It provides a comparative analysis of intrinsic variability, dust extinction, and microlensing as causes of chromaticity, highlighting microlensing as the more plausible explanation.

Findings

Intrinsic variability cannot explain observed chromaticity.

Dust extinction and microlensing can reproduce color differences.

Microlensing is more realistic than dust extinction when considering observation timing.

Abstract

Aims:In some of the lensed quasars, color differences between multiple images are observed at optical/near-infrared wavelengths. There are three possible origins of the color differences: intrinsic variabilities of quasars, differential dust extinction, and quasar microlensing. We examine how these three possible scenarios can reproduce the observed chromaticity. Methods:We evaluate how much color difference between multiple images can be reproduced by the above three possible scenarios with realistic models; (i) an empirical relation for intrinsic variabilities of quasars, (ii) empirical relations for dust extinction and theoretically predicted inhomogeneity in galaxies, or (iii) a theoretical model for quasar accretion disks and magnification patterns in the vicinity of caustics. Results:We find that intrinsic variabilities of quasars cannot be a dominant source responsible for observed chromatic features in multiple quasars. In contrast, either dust extinction or quasar microlensing can nicely reproduce the observed color differences between multiple images in most of the lensed quasars. Taking into account the time interval between observations at different wavebands in our estimations, quasar microlensing is a more realistic scenario to reproduce the observed color differences than dust extinction. All the observed color differences presented in this paper can be explained by a combination of these two effects, but monitoring observations at multiple wavebands are necessary to disentangle these.