A microlensing study of the accretion disc in the quasar MG 0414+0534

TL;DR

This study uses single-epoch multi-band imaging to constrain the size and wavelength dependence of the quasar MG 0414+0534's accretion disc, providing insights into its structure with a novel observational approach.

Contribution

It introduces a new technique for estimating quasar accretion disc sizes from single-epoch data, reducing the need for long-term monitoring.

Findings

Placed an upper limit on the emission region size in the r'-band

Constrained the power-law index of size-wavelength relation

Found consistency with the Shakura-Sunyaev thin disc model

Abstract

Observations of gravitational microlensing in multiply imaged quasars currently provide the only direct probe of quasar emission region structure on sub-microarcsecond scales. Analyses of microlensing variability are observationally expensive, requiring long-term monitoring of lensed systems. Here we demonstrate a technique for constraining the size of the quasar continuum emission region as a function of wavelength using single-epoch multi-band imaging. We have obtained images of the lensed quasar MG 0414+0534 in five wavelength bands using the Magellan 6.5-metre Baade telescope at Las Campanas Observatory, Chile. These data, in combination with two existing epochs of Hubble Space Telescope data, are used to model the size of the continuum emission region $\sigma$ as a power-law in wavelength, $\sigma\propto\lambda^\nu$. We place an upper limit on the Gaussian width of the $r^\prime$-band emission region of $1.80 \times 10^{16} h_{70}^{-1/2} (<M>/\rmn{M}_{\odot})^{1/2}$cm, and constrain the power-law index to $0.77\leq\nu\leq2.67$ (95 per cent confidence range). These results can be used to constrain models of quasar accretion discs. As a example, we find that the accretion disc in MG 0414+0534 is statistically consistent with a Shakura-Sunyaev thin disc model.