Large Magellanic Cloud self-lensing for OGLE-II microlensing observations

In the framework of microlensing searches towards the Large Magellanic Cloud (LMC), we discuss the results presented by the Optical Gravitational Lensing Experiment (OGLE) collaboration for their OGLE-II campaign (Wyrzykowski et al). We evaluate the optical depth, the duration and the expected rate of events for the different possible lens populations: both luminous, dominated by the LMC self-lensing, and 'dark', the would be compact halo objects (massive compact halo objects) belonging to either the Galactic or the LMC halo. The OGLE-II observational results, two microlensing candidate events located in the LMC bar region with duration of 24.2 and 57.2 days, compare well with the expected signal from the luminous lens populations: n exp = 1.5, with typical duration, for LMC self-lensing, of about 50 days. Because of the small statistics at disposal, however, the conclusions that can be drawn as for the halo mass fraction, f , in the form of compact halo objects are not too severe. By means of a likelihood analysis we find an upper limit for f , at 95 per cent confidence level, of about 15 per cent in the mass range (10 -2 -10 -1 ) M and 26 per cent for 0.5 M .