Expected EAGLE event rate towards the Magellanic Clouds

Abstract

We propose to search for MACHOs by observing EAGLE (Extremely Amplified Gravitational LEnsing) events of a majority of dim stars. This search is independent of the usual one. For the detection limit of EAGLE (about 20 mag), about 100 f (τ^{LMC} / 3 \times 10^{-7}) (100 days / <t>) EAGLE events/y are expected to result from all the dim stars in LMC. Here τ^{LMC} and <t> are the optical depth and the average duration of microlensing events, respectively, while f (0 < f < 1) is a parameter depending on the unknown stellar luminosity function. The observed mean duration of EAGLE events also depends on the luminosity function and is (0.01 - 0.4) times the usual duration of microlensing events, which corresponds to (1 - 30) days. The follow-up observation using larger telescopes may enable us to determine the impact parameter and the true duration of the event. If f is determined by another independent method, we can also determine τ^{LMC}. Even if f is undetermined, the detection of EAGLE events strongly suggest that MACHOs are not due to variable source stars, since EAGLE events are due to the dim main-sequence stars. Although for the SMC, the event rate is smaller by a factor of about 7, it is still a substantial number (about 13 f (τ^{SMC} / 3 \times 10^{-7} (100 days / <t>) events/y).