Microlensing Optical Depth of the Large Magellanic Cloud

Abstract

The observed microlensing events towards the LMC do not have yet a coherent explanation. If they are due to Galactic Halo objects, the nature of these objects is puzzling --- half the halo in dark 0.5 Msol objects. On the other hand, traditional models of the LMC predict a self-lensing optical depth about an order of magnitude too low, although characteristics of some of the observed events favor a self-lensing explanation. We present here two models of the LMC taking into account the correlation between the mass of the stars and their velocity dispersion: a thin Mestel disk, and an ellipsoidal model. Both yield optical depths, event rates, and event duration distributions compatible with the observations. The grounds for such models are discussed, as well as their observational consequences.