EXPECTED COLOR VARIATIONS OF THE GRAVITATIONALLY MICROLENSED QSO 2237+0305

The continuum source of a quasar may have different sizes in different wavelengths. When such a source crosses a caustic due to gravitational microlensing the observed color will change. We show typical light curves and the corresponding color curves for our model of QSO 2237 + 0305A, the image that has been reported to vary. We present probabilities for color changes of certain amplitudes as functions of the observed magnitude changes for different time intervals between the two observational epochs, different source sizes, and different source size ratios. It may be possible to find the ratio of the continuum source sizes in the two color bands, once a color change correlated with a continuum change is found. With a few observations showing the shape of a color event one may even determine the absolute size of the quasar in the continuum.