The SuperMACHO Survey

An elegant way to further our understanding of dark matter halos and to search for astrophysical dark matter candidates is to utilize the defining feature of the dark matter: the effect of its gravitational field. In the mid-90s, several groups established microlensing searches toward the Large Magellanic Cloud (LMC) and other nearby galaxies.  The MACHO group reported 13-17 microlensing events toward the LMC, which significantly exceeds the number expected from lenses in known populations.  This raises the question of where the lenses reside.  Unfortunately the main observable in any given microlensing event, its duration, depends upon a combination of lens mass, position, and velocity relative to the source.  Any conclusion about the spatial location of the lens population therefore depends upon the assumptions made about its mass and velocity.

The SuperMACHO Project is an ongoing five-year microlensing survey of the LMC that is being carried out with the specific goal of answering the question: ``Where do the lenses responsible for the measured event rates toward the LMC reside?''. We have designed our survey to provide a significant increase in the number of detected events. This will allow a more robust assessment of the spatial variation of the microlensing optical depth across the face of the LMC, and will clarify whether the observed optical depth can be accounted for by LMC self-lensing --- the most popular alternative to lensing by MACHO's.

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