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E. Agol, J. Krolik (Johns Hopkins Univ.)
The Einstein Cross is a gravitationally lensed quasar which undergoes variations due to microlensing by stars in the lens galaxy. Microlensing constrains the size of the optical emission region to be less than 2x1015 cm. Future IR/optical/UV monitoring will allow us to map out the surface brightness of the quasar by inversion of the lightcurve during a high amplification microlensing event. If the quasar is powered by geometrically thin, azimuthally symmetric accretion onto a black hole, then the lightcurve can also be inverted to obtain the surface brightness at the accretion disk. We perform the inversion using a regularization constraint, and find that we can reproduce the surface brightness quite well (to 30% near the peak) for accretion disk models which are consistent with the dereddened data, assuming that we have 1% photometry from K band to near UV at 40 points during a clean high amplification event. We can also constrain the inclination angle and size of the black hole (if the caustic velocity is known). We cannot constrain the black hole spin.
The author(s) of this abstract have provided an email address for comments about the abstract: agol@pha.jhu.edu