Event rates and timescale distributions from realistic microlensing models of M31

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  • 4 January 2002
Abstract
We provide a set of microlensing event rate maps for M31, the Andromeda Galaxy. Rates for Andromeda microlensing were calculated on the basis of a four component model of the lens and source populations: disk and bulge sources lensed by bulge, disk, M31 halo and Galactic halo lenses. We confirm the high rate gradient along the M31 minor axis due to a dark halo of lenses. Furthermore, we compute the timescale distributions for events, both Einstein times and full-width at half-maximum times. We explore how the shapes of the rate contours and the timescale distributions can be used to measure the shape and extent of the microlensing halo. With one year of twice--weekly sampling, or three observing seasons, a halo MACHO fraction as small as 5% can be detected with modest ground based telescopes.

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