The Nature and Size of the Optical Continuum Source in QSO 2237+0305

From the peak of a gravitational microlensing high-magnification event in theA component of QSO 2237+0305, which was accurately monitored by the GLITPcollaboration, we derived new information on the nature and size of the opticalV-band and R-band sources in the far quasar. If the microlensing peak is causedby a microcaustic crossing, we firstly obtained that the standard accretiondisk is a scenario more reliable/feasible than other usual axially symmetricmodels. Moreover, the standard scenario fits both the V-band and R-bandobservations with reduced chi-square values very close to one. Taking intoaccount all these results, a standard accretion disk around a supermassiveblack hole is a good candidate to be the optical continuum main source in QSO2237+0305. Secondly, using the standard source model and a robust upper limiton the transverse galactic velocity, we inferred that 90 per cent of the V-bandand R-band luminosities are emitted from a region with radial size less than1.2 10^{-2} pc (= 3.7 10^{16} cm, at 2*sigma confidence level).Comment: ApJ, in press (LaTeX, 28 pages, 6 eps figures