Source size measurement from observed quasar microlensing

Recently, the OGLE team have reported a clear quasar microlensing signal in Q2237+0305. I have analyzed the microlens event of 'image C' by using thei r finely and densely sampled light curves. From light curve fitting, I unam biguously set the source size of less than or equal to0.98 Einstein-Ring ra dius as a conservative limit. This limit corresponds to 2000 AU, if I adopt M-lens similar to0.1M(circle dot) obtained by a recent statistical study o f the mean mass of the lens object. This gives clear evidence for the exist ence of an accretion disk in the central region of the quasar.