David Floyd
OCIW/AAO Magellan Fellow, Las Campanas Observatory & Gemini South Visiting Scientist
 

"Examining Quasar Accretion Disks Through Microlensing"
 

I present a novel method of constraining AGN emission region size and emission mechanism, using recent optical-NIR imaging from the Magellan telescopes of "anomalous" lensed quasars. Anomalous lensed quasars have an image pair in which one of the images is unusually ("anomalously") dim. We rule out millilensing and partial obscuration as causes for the anomalous flux ratio in each of our quasars, leaving microlensing as the only plausible alternative. We generate magnification maps for each image using a range of smooth-to-clumpy matter fractions. We then randomly select source positions on the map and calculate the magnifications of a set of Gaussian sources of varying width.  We are thus able to constrain statistically, both the proportion of smooth-to-clumpy lensing material, and the size of the emitting region of the lensed source. Using this technique we have probed down to unprecedented scale lengths in the central engine (< 7 light days in r' band) and have begun to explore the change with wavelength. We find clear evidence of a decrease in source size with wavelength, and can place meaningful constraints on possible emission mechanisms, which are beginning to challenge the standard Shakura-Sunyaev model.