Optimal Microlensing Observations

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One of the major limitations of microlensing observations toward the Large Magellanic Cloud (LMC) is the low rate of event detection. What can be done to improve this rate? Is it better to invest telescope time in more frequent observations of the inner high-surface-brightness fields or in covering new, less populated outer fields? How would a factor 2 improvement in CCD sensitivity affect the detection efficiency? Would a series of major (factor 2-4) upgrades in telescope aperture, seeing, sky brightness, camera size, and detector efficiency increase the event rate by a huge factor, or only marginally? I develop a simplified framework to address these questions. With observational resources fixed at the level of the MACHO and EROS experiments, the biggest improvement (factor ~2) would come by reducing the time spent on the inner ~25 deg^2 and applying it to the outer ~100 deg^2. By combining this change with the characteristics of a good medium-size telescope (2.5 m mirror, 1'' point-spread function, thinned CCD chips, 1 deg^2 camera, and dark sky), it should be possible to increase the detection of LMC events to more than 100 yr^-1 (assuming current estimates of the optical depth apply to the entire LMC).



dark matter, Galaxy: halo, gravitational lensing, Magellanic Clouds


Andrew Gould, "Optimal Microlensing Observations," The Astrophysical Journal 517, no. 2 (1999), doi:10.1086/307214