The influence of microlensing on spectral line shapes generated by a relativistic accretion disc

We study the influence of gravitational microlensing on the spectral line p rofiles originating from a relativistic accretion disc. Using the Chen & Ha lpern model for the disc, we show the noticeable changes that microlensing can induce in the line shape when the Einstein radius associated with the m icrolens is of a size comparable to that of the accretion disc. Of special interest is the relative enhancement between the blue and red peaks of the line when an off-center microlens affects the approaching and receding part s of the accretion disc asymmetrically. In an AGN formed by a super-massive binary in which the accretion disc is l ocated around one of the supermassive companions (the primary), we discuss the possibility of microlensing by the secondary. In this case the ratio be tween the blue and red peaks of the line profile would depend on the orbita l phase. We have also considered the more standard configuration of microle nsing by a star-sized object in an intervening galaxy and find that microle nsing may also be detected in the broad emission lines of multiply imaged Q SOs. The changes observed in the line profile of Arp 102 B are taken as a r eference for exploring both scenarios.