Eric Agol
JHU

Imaging a Quasar Accretion Disk with Microlensing

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 $2x10^{15}$ 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 will also be able to constrain the inclination
angle of the disk, the spin of the black hole, and size of the black
hole
(if the caustic velocity is known).