On the Mass of the Gravitational Lenses in Lmc

The microlensing surveys towards the Large Magellanic Cloud (LMC) have demonstrated the existence of compact objects that act as gravitational lenses somewhere between us and LMC. Besides the 4 events found by the EROS2 group [1], the MACHO Project has detected 16 events and its maximum likelihood estimate of the mass of the lensing objects is ≈ 0.5 M⊙, while the fraction f of dark matter in form of MACHOs in the Galactic halo is estimated to be ∼ 20% [2]. However, the interpretation of these data is a matter of controversy and other hypothesis have been proposed: the possibility that the lenses are located in LMC itself instead as in the Galactic halo was claimed by Sahu [3]; a warp of the Milky Way (MW) disk, which covers the line of sight towards LMC, has been proposed to support a lens disk population [4]; Zhao [5] has suggested instead that the debris torn from the LMC by tidal forces may be a source of MACHOs; a non planar geometry of LMC, i.e. a misalignment of the bar from the the disk, has been proposed by Zhao & Evans [6]; other authors have considered LMC components fatter than is conventional, with material extending to scale heights of ∼ 6 kpc above the plane of the LMC disk [7], as is suggested by Weinberg [8] numerical simulations of the evolution of the LMC in the tidal field of the MW. The analysis of Jetzer et al. [9] has shown that possibly the observed events are distributed among different galactic components (disk, spheroid, galactic halo, LMC halo and self-lensing). This means that the lenses do not belong all to the same population and their astrophysical features can