Strong microlensing and BL LAC objects

Abstract

Macrolensing and microlensing are combined to study the probability of quasars being strongly microlensed by isolated intervening galaxies. The macrolensing model is described in Mao (1991), with the velocity dispersions and local number densities for different types of galaxies from Fukugita and Turner (1991). The magnification probability distributions for microlensing are adopted from Narayan (1989). Using Monte Carlo simulation, we calculate the distributions of redshifts of the lensing galaxies and angular separations between the Tensing galaxies and the microlensed quasars for strong microlensing events. These strongly microlensed quasars may have very weak emissions lines, thus they may look like BL Lac objects (Ostriker and Vietri 1985, 1990). Our preliminary results show that the distribution of redshifts of the lensing galaxies is similar to that expected for multiply imaged quasars (cf. Turner, Ostriker, and Gott 1984, Figure 5), but with a different amplitude. The probability distribution has no peaks close to the observer or to the source, therefore gravitational lensing could not explain the local overdensity of BL Lac Objects.