A new analysis of the MEGA M 31 microlensing events

¹ Dipartimento di Fisica, Università di Lecce and INFN, Sezione di Lecce, CP 193, 73100 Lecce, Italy e-mail: nucita@le.infn.it
² Dipartimento di Fisica “E. R. Caianiello”, Università di Salerno, 84081 Baronissi (SA) and INFN, Sezione di Napoli, Italy
³ Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland

Received: 16 June 2006
Accepted: 3 October 2006

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.