A new analysis of the MEGA M 31 microlensing events

Abstract

We discuss the results of the MEGA microlensing campaign towards M 31. Our analysis is based on analytically evaluating the microlensing rate, taking the observational efficiency into account as given by the MEGA collaboration. In particular, we studied the spatial and time-duration distributions of the microlensing events for several mass distribution models of the M 31 bulge. We find that only for extreme models of the M 31 luminous components is it possible to reconcile the total observed MEGA events with the expected self-lensing contribution. Nevertheless, the expected spatial distribution of self-lensing events is more concentrated and hardly agrees with the observed distribution. We thus find it difficult to explain all events as due to self-lensing alone. On the other hand, the small number of events does not yet allow firm conclusions to be drawn on the halo dark matter fraction in the form of MACHOs.