Self‐lensing Models of the Large Magellanic Cloud

All of the proposed explanations for the microlensing events observed towardsthe LMC have difficulties. One of these proposed explanations, LMCself-lensing, which invokes ordinary LMC stars as the long sought-after lenses,has recently gained considerable popularity as a possible solution to themicrolensing conundrum. In this paper, we carefully examine the set of LMCself-lensing models. In particular, we review the pertinent observations madeof the LMC, and show how these observations place limits on such self-lensingmodels. We find that, given current observational constraints, no purely LMCdisk models are capable of producing optical depths as large as that reportedin the MACHO collaboration 2-year analysis. Besides pure disk, we also consideralternate geometries, and present a framework which encompasses the previousstudies of LMC self-lensing. We discuss which model parameters need to bepushed in order for such models to succeed. For example, like previous workers,we find that an LMC halo geometry may be able to explain the observed events.However, since all known LMC tracer stellar populations exhibit disk-likekinematics, such models will have difficulty being reconciled withobservations. For SMC self-lensing, we find predicted optical depths differingfrom previous results, but more than sufficient to explain all observed SMCmicrolensing. In contrast, for the LMC we find a self-lensing optical depthcontribution between 0.47e-8 and 7.84e-8, with 2.44e-8 being the value for theset of LMC parameters most consistent with current observations.Comment: 20 pages, Latex, 14 figures, submitted to Ap