Microlensing Induced Spectral Variability In Q2237+0305

Several macrolensed systems exhibit photometric variability consistent with microlensing due to objects of stellar mass located in the lens. The degree of microlensing amplification is dependent upon the size of the source, with smaller sources being more amplified. In general, amplification of sources larger than an Einstein radius projected onto the source plane is negligible. For the quasar Q2237+0305, a quadrupole image lens (Huchra et al., 1985), this radius is 0.05 pc, larger than the predicted size of a continuum emitting accretion disk, but substantially smaller than the broad line region (Figure 1). This scale difference implies that the continuum will be amplified while the broad line emission remains essentially unchanged during a microlensing event (Sanitt, 1971; Kayser et al., 1986). The broad line emitting region, as a whole, is too large to be microlensed, but substructure on small scales may be significantly amplified. Although the total flux in the line is relatively unchanged, microlensing of substructure can result in changes in the shape of the emission line profiles, and produce measurable shifts in the central wavelength of the line (Nemiroff, 1988; Schneider and Wambsganss, 1990).