David Pooley
University of Wisconsin at Madison
Zooming in on Quasar Emission Regions through Gravitational Lensing
Wednesday, February 27, 2008, 4:00 p.m.
Refreshments at 3:45 p.m.
ABSTRACT
Under favorable conditions, the light from a distant quasar (an
actively accreting supermassive black hole) can be gravitationally
lensed by an intervening galaxy to produce four images of the
quasar. I will discuss an innovative technique of analyzing these
quadruply-lensed quasars in optical and X-ray emission that, for the
first time, is able to resolve the structure of the accretion disk
around the black hole. I will present X-ray observations of ten
lensed quasars recorded with the Chandra X-ray Observatory as well as
corresponding optical data obtained with either the Hubble Space
Telescope or ground-based telescopes. The X-ray and optical
observations together provide a micro-arcsecond probe of the quasar,
an angular resolution far beyond the reach of current and future
telescopes. Emphasis will be on the anomalies between the observed
flux ratios and the predictions of lensing models. These anomalies
allow us to conclude that the optical emission regions of quasar
accretion disks are larger than expected from standard disk models by
factors of ~3-30. I will also discuss how these same flux ratio
anomalies can be used to determine the amount of dark matter in the
lensing galaxy.