# Accretion Disk Size Measurement and Time Delays in the Lensed Quasar WFI 2033-4723

## TL;DR

This study measures the accretion disk size and time delays in the lensed quasar WFI 2033-4723 using 13 seasons of photometry, confirming previous delays and updating the disk size-mass relation with new microlensing analysis.

## Contribution

It introduces a Bayesian Monte Carlo method to estimate the accretion disk size and refines the quasar time delay measurements, updating the disk size-mass relation.

## Key findings

- Accretion disk size measured as log(r_s/cm)=15.86^{+0.25}_{-0.27}.
- Confirmed previous time delays between quasar images.
- Updated the disk size-black hole mass relation, showing simple thin disk theory underestimates disk sizes.

## Abstract

We present 13 seasons of $R$-band photometry of the quadruply-lensed quasar WFI 2033-4723 from the 1.3m SMARTS telescope at CTIO and the 1.2m Euler Swiss Telescope at La Silla, in which we detect microlensing variability of $\sim0.2$ mags on a timescale of $\sim$6 years. Using a Bayesian Monte Carlo technique, we analyze the microlensing signal to obtain a measurement of the size of this system's accretion disk of $\log (r_s/{\rm cm}) = 15.86^{+0.25}_{-0.27}$ at $\lambda_{rest} = 2481{\rm \AA}$, assuming a $60^\circ$ inclination angle. We confirm previous measurements of the BC and AB time delays, and we obtain a tentative measurement of the delay between the closely spaced A1 and A2 images of $\Delta t_{A1A2} = t_{A1} - t_{A2} = -3.9^{+3.4}_{-2.2}$ days. We conclude with an update to the Quasar Accretion Disk Size - Black Hole Mass Relation, in which we confirm that the accretion disk size predictions from simple thin disk theory are too small.