Caustic Crossing in the Gravitational Lens Q2237+0305

The monitoring of the gravitational lens Q2237+0305 carried out by the OGLE group during 1997--1999 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 < 10^(15) 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