Gravitational Lensing Size Scales for Quasars

TL;DR

This paper reviews multi-wavelength monitoring of lensed quasars, revealing that optical sizes are larger than theoretical predictions, and constrains the emission regions and accretion disk properties through microlensing and caustic crossing analyses.

Contribution

It provides new size estimates of quasar emission regions across wavelengths and demonstrates the use of microlensing events to probe black hole accretion disk parameters.

Findings

Optical sizes exceed thin-disk model predictions.

X-ray emission regions vary in size, with some being more compact.

Microlensing caustic crossings constrain the ISCO radius and disk inclination.

Abstract

We review results from our monitoring observations of several lensed quasars performed in the optical, UV, and X-ray bands. Modeling of the multi-wavelength light curves provides constraints on the extent of the optical, UV, and X-ray emission regions. One of the important results of our analysis is that the optical sizes as inferred from the microlensing analysis are significantly larger than those predicted by the theoretical-thin-disk estimate. In a few cases we also constrain the slope of the size-wavelength relation. Our size constraints of the soft and hard X-ray emission regions of quasars indicate that in some objects of our sample the hard X-ray emission region is more compact than the soft and in others the soft emission region is smaller. This difference may be the result of the relative strengths of the disk-reflected (harder and extended) versus corona-direct (softer and compact) components in the quasars of our sample. Finally, we present the analysis of several strong microlensing events where we detect an evolution of the relativistic Fe line profile as the magnification caustic traverses the accretion disk. These caustic crossings are used to provide constraints on the innermost stable circular orbit (ISCO) radius and the accretion disk inclination angle of the black hole in quasar RX J1131-1231.