Constraining the Location of Microlensing Objects by using the Finite Source Effect in EAGLE events

We propose a new method to constrain the location of microlensing objects using EAGLE (Extremely Amplified Gravitational LEnsing) events. We have estimated the rate of EAGLE events by taking the finite-source effect into account. We found that the EAGLE event rate for using a 1-m class telescope whose limiting magnitude is V ∼ 21 is the same as or higher than that of the ordinary microlensing events which have been found to date. We have also found that the fraction of transit EAGLE events is large enough to detect: between 4 ∼ 80% depending on the lens location. Since the lens proper motion can be measured for a transit event, one can distinguish whether the lens is a MACHO (MAssive Compact Halo Object) in our halo or one of the known stars in the Large Magellanic Cloud (LMC) from the proper motion measurement for each transit EAGLE event. Moreover, we show that the fraction of transit EAGLEs in all EAGLE events significantly depends on the lensing locations: the transit EAGLE fraction for the self-lensing case is 2 ∼ 15 times larger than that for halo MACHOs. Thus, one can constrain the location of lens objects by the statistics of the transit events fraction. We show that we can reasonably expect 0 ∼ 6 transit events out of 21 EAGLE events in 3 years. We can also constrain the lens population properties at a greater than 99% confidence level depending on the number of transit events detected. We also present the duration of EAGLE events, and show how an hourly observational mode is more suitable for an EAGLE event search program. Subject headings: dark matter—Galaxy:halo—gravitational lensing—Magellanic Cloud