Gurtina Besla, Lars Hernquist, Abraham Loeb
We introduce a novel theory to explain the long-standing puzzle of the nature of the microlensing events reported towards the Large Magellanic Cloud (LMC) by the MACHO and OGLE collaborations. We propose that a population of tidally stripped stars from the Small Magellanic Clouds (SMC) located ~4-10 kpc behind a lensing population of LMC disk stars can naturally explain the observed event durations, event frequency and spatial distribution of the reported events. These results favor a scenario for the interaction history of the Magellanic Clouds wherein the Clouds are on their first infall towards the Milky Way and the SMC has recently collided with the LMC, leading to a large number of faint sources distributed non-uniformly behind the LMC disk. Owing to the tidal nature of the source population, the sources exhibit a range of distances and velocities with respect to the LMC lenses, naturally explaining the observed range of event durations (30-220 days). Assuming a detection efficiency of 30-50% we find event frequencies of ~1-2 /yr in the central regions of the LMC disk; comparable to the observed rate for the MACHO survey, ~2 /yr. A lower detection efficiency of 10% yields an event frequency of ~0.46 /yr across a larger area of the LMC disk; comparable to that reported by the less sensitive OGLE survey, ~0.33 /yr. In contrast to self-lensing models, microlensing events are also expected to occur in fields off the LMC's stellar bar since the stellar debris is not expected to be concentrated in the bar region. This scenario leads to a number of observational tests: the sources are low-metallicity SMC stars, they exhibit high velocities relative to LMC disk stars that may be detectable via proper motion studies, and, most notably, there should exist a stellar counterpart to the gaseous Magellanic Stream and Magellanic Bridge with a V-band surface brightness > 34 mag/arcsec^2.
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http://arxiv.org/abs/1205.4724
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