A&A 445, 375-385 (2006)
Monte Carlo analysis of MEGA microlensing events towards M 31G. Ingrosso1, S. Calchi Novati2, F. De Paolis1, Ph. Jetzer2, A. A. Nucita1 and F. Strafella1
1 Dipartimento di Fisica, Università di Lecce and INFN, Sezione di Lecce, CP 193, 73100 Lecce, Italy
2 Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
(Received 24 May 2005 / Accepted 6 September 2005)
We perform an analytical study and a Monte Carlo (MC) analysis of the main features for microlensing events in pixel lensing observations towards M 31. Our main aim is to investigate the lens nature and location of the 14 candidate events found by the MEGA collaboration. Assuming a reference model for the mass distribution in M 31 and the standard model for our galaxy, we estimate the MACHO-to-self lensing probability and the event time duration towards M 31. Reproducing the MEGA observing conditions, as a result we get the MC event number density distribution as a function of the event full-width half-maximum duration t1/2 and the magnitude at maximum . For a MACHO mass of we find typical values of day and , for both MACHO-lensing and self-lensing events occurring beyond about 10 arcmin from the M 31 center. A comparison of the observed features (t1/2 and ) with our MC results shows that for a MACHO mass the four innermost MEGA events are most likely self-lensing events, whereas the six outermost events must be genuine MACHO-lensing events.
Key words: gravitational lensing -- galaxy: halo -- galaxies: individuals: M 31
© ESO 2005