Time Delay and Accretion Disk Size Measurements in the Lensed Quasar SBS
  0909+532 from Multiwavelength Microlensing Analysis
  We present three complete seasons and two half-seasons of SDSS r-band
photometry of the gravitationally lensed quasar SBS 0909+532 from the U.S.
Naval Observatory, as well as two seasons each of SDSS g-band and r-band
monitoring from the Liverpool Robotic Telescope. Using Monte Carlo simulations
to simultaneously measure the system's time delay and model the r-band
microlensing variability, we confirm and significantly refine the precision of
the system's time delay to \Delta t_{AB} = 50^{+2}_{-4} days, where the stated
uncertainties represent the bounds of the formal 1\sigma\ confidence interval.
There may be a conflict between the time delay measurement and a lens
consisting of a single galaxy. While models based on the Hubble Space Telescope
astrometry and a relatively compact stellar distribution can reproduce the
observed delay, the models have somewhat less dark matter than we would
typically expect. We also carry out a joint analysis of the microlensing
variability in the r- and g-bands to constrain the size of the quasar's
continuum source at these wavelengths, obtaining log[(r_{s,r}/cm)
[cos{i}/0.5]^{1/2}] = 15.3 \pm 0.3 and log[(r_{s,g}/cm) [cos{i}/0.5]^{1/2}] =
14.8 \pm 0.9, respectively. Our current results do not formally constrain the
temperature profile of the accretion disk but are consistent with the
expectations of standard thin disk theory.
