Q2237+0305 source structure and dimensions from light-curve simulation

Assuming a two-component quasar structure model consisting of a central compact source and an extended outer feature, we produce microlensing simulations for a population of compact masses in the lensing galaxy of Q2237+0305. Such a model is a simplified version of that adopted to explain the brightness variations observed in Q0957. The microlensing light curves generated for a range of source parameters were compared to the light curves obtained in the framework of the Optical Gravitational Lensing Experiment program. With a large number of trials, we built, in the domain of the source structure parameters, probability distributions to find ‘good’ realizations of light curves. The values of the source parameters which provide the maximum of the joint probability distribution calculated for all the image components have been accepted as estimates for the source structure parameters. The results favour the two-component model of the quasar brightness structure over a single compact central source model, and in general the simulations confirm the Schild–Vakulik model that previously described successfully the microlensing and other properties of Q0957. Adopting 3300 km s−1 for the transverse velocity of the source, the effective size of the central source was determined to be about 2 × 1015 cm, and ɛ≈ 2 was obtained for the ratio of the integral luminosity of the outer feature to that of the central source.