Self-lensing models of the large magellanic cloud

All of the proposed explanations for the microlensing events observed towar d the LMC have difficulties. One of these proposed explanations, LMC self-l ensing, which invokes ordinary LMC stars as the long sought-after lenses, h as recently gained considerable popularity as a possible solution to the mi crolensing conundrum. In this payer, we carefully examine the full range of LMC self-lensing models, including for the first time the contribution of the LMC bar in both sources and lenses. In particular, we review the pertin ent observations made of the LMC and show how these observations glace limi ts on such self-lensing models. We find that, given current observational c onstraints, no purely LMC disk models are capable of producing optical dept hs as large as that reported in the MACHO collaboration 2 year analysis. We also introduce a new quantitative measure of the central concentration of the microlensing events and show that it discriminates well between disk/ba r self-lensing and halo microlensing. Besides pure disk/bar, we also consid er alternative geometries and present a framework which encompasses the pre vious studies of LMC self-lensing. We discuss which model parameters need t o be pushed 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 obse rved events. However, since all known LMC tracer stellar populations exhibi t disklike kinematics, such models will have difficulty being reconciled wi th observations. For SMC self-lensing, we find predicted optical depths dif fering from previous results, but more than sufficient to explain all obser ved SMC microlensing. In contrast, for the LMC we find a self-lensing optic al depth contribution between 0.47 x 10(-8) and 7.84 x 10(-8), with 2.44 x 10(-8) being the value for the set of LMC parameters most consistent with c urrent observations.