A Study of Gravitational Lens Chromaticity with the Hubble Space Telescope

TL;DR

This study uses Hubble Space Telescope data to analyze the chromatic properties of six gravitational lenses, revealing dust extinction characteristics and microlensing effects that inform on quasar accretion disk structure.

Contribution

It provides new measurements of dust extinction curves and quasar accretion disk sizes using multi-filter observations of gravitational lenses.

Findings

Dust extinction curves characterized for three systems.

Detection and analysis of chromatic microlensing in one system.

Estimated size and wavelength dependence of the quasar accretion disk.

Abstract

We report Hubble Space Telescope observations of 6 gravitational lenses with the Advanced Camera for Surveys. We measured the flux ratios between the lensed images in 6 filters from 8140\AA\ to 2200\AA. In 3 of the systems, HE0512$-$3329, B1600+434, and H1413+117, we were able to construct UV extinction curves partially overlapping the 2175\AA\ feature and characterize the properties of the dust relative to the Galaxy and the Magellanic Clouds. In HE1104$-$1804 we detect chromatic microlensing and use it to study the physical properties of the quasar accretion disk. For a Gaussian model of the disk $\exp(-r^2/2 r_s^2)$, scaling with wavelength as $r_s \propto \lambda^p$, we estimate $r_s(\lambda3363)=4^{+4}_{-2}$ ($7\pm 4$) light-days and $p=1.1\pm 0.6$ ($1.0\pm 0.6$) for a logarithmic (linear) prior on $r_s$. The remaining two systems, FBQ0951+2635 and SBS1520+530, yielded no useful estimates of extinction or chromatic microlensing.