Microlensing of the Lensed Quasar SDSS 0924+0219

We analyze V-, I-, and H-band HST images and two seasons of R-band monitoring data for the gravitationally lensed quasar SDSS 0924+0219. We clearly see that image D is a point-source image of the quasar at the center of its host galaxy. We can easily track the host galaxy of the quasar close to image D because microlensing has provided a natural coronograph that suppresses the flux of the quasar image by roughly an order of magnitude. We observe low-amplitude, uncorrelated variability between the four quasar images due to microlensing, but no correlated variations that could be used to measure a time delay. Monte Carlo models of the microlensing variability provide estimates of the mean stellar mass in the lens galaxy (0.03 h2 M☉ ≲ ⟨M⟩ ≲ 2.0 h2 M☉), the accretion disk size (the disk temperature is 5 × 104 K at 1.3 × 1014 h-1 cm ≲ rs ≲ 4.7 × 1014 h-1 cm), and the black hole mass (6.6 × 106 M☉ ≲ MBH h3/2 η (L/LEdd)1/2 ≲ 4.4 × 107 M☉), all at 68% confidence. The black hole mass estimate based on microlensing is mildly inconsistent with an estimate of MBH = (2.8 ± 0.9) × 108 M☉ from the Mg II emission-line width. If we extrapolate the best-fitting light curve models into the future, we expect images A and B to fade and images C and D to brighten. In particular, we estimate that image D has a roughly 16% probability of brightening by a factor of 2 during the next year and a 40% probability of brightening by an order of magnitude over the next decade.