The multiple quasar Q2237 0305 under a microlensing caustic

Abstract

We use the high magnification event seen in the 1999 OGLE campaign light curve of image C of the quadruply imaged gravitational lens Q2237+0305 to study the structure of the quasar engine. We have obtained - and -band photometry at the Apache Point Observatory 3.5 m telescope where we find that the event has a smaller amplitude in the -band than in the - and OGLE -bands. By comparing the light curves with microlensing simulations we obtain constraints on the sizes of the quasar regions contributing to the - and -band flux. Assuming that most of the surface mass density in the central kiloparsec of the lensing galaxy is due to stars and by modeling the source with a Gaussian profile, we obtai..