Caustic crossing in the gravitational lens Q2237+0305

The monitoring of the gravitational lens Q2237+0305 carried out by the OGLE group during 1997–2000 is analyzed. The significant light amplifications in the C and A quasar components with maxima in mid-and late 1999, respectively, are interpreted as the crossing of microlens caustics by the source. A constraint on the emitting-region size R≤1015 cm has been obtained from the light-curve shape by assuming a power-law quasar brightness distribution (r 2+R 2)−p . To estimate the exponent p∼1.2 requires refining the standard model for the quasar continuum formation in an optically thick accretion disk with p=1.5.