A Microlensing Accretion Disk Size Measurement in the Lensed Quasar WFI
  2026-4536
  We use thirteen seasons of R-band photometry from the 1.2m Leonard Euler
Swiss Telescope at La Silla to examine microlensing variability in the
quadruply-imaged lensed quasar WFI 2026-4536. The lightcurves exhibit
${\sim}\,0.2\,\text{mag}$ of uncorrelated variability across all epochs and a
prominent single feature of ${\sim}\,0.1\,\text{mag}$ within a single season.
We analyze this variability to constrain the size of the quasar's accretion
disk. Adopting a nominal inclination of 60$^\text{o}$, we find an accretion
disk scale radius of $\log(r_s/\text{cm}) = 15.74^{+0.34}_{-0.29}$ at a
rest-frame wavelength of $2043\,\unicode{xC5}$, and we estimate a black hole
mass of $\log(M_{\text{BH}}/M_{\odot}) = 9.18^{+0.39}_{-0.34}$, based on the
CIV line in VLT spectra. This size measurement is fully consistent with the
Quasar Accretion Disk Size - Black Hole Mass relation, providing another system
in which the accretion disk is larger than predicted by thin disk theory.
