ar X iv : a st ro - p h / 01 02 38 4 v 1 2 2 Fe b 20 01 Caustic Crossing in the Gravitational Lens Q 2237 + 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.