The Use of High‐Magnification Microlensing Events in Discovering Extrasolar Planets

Abstract

Hundreds of gravitational microlensing events have now been detected toward the Galactic bulge, with many more to come. The detection of ne structure in these events has been theorized as an excellent way to discover extrasolar planetary systems along the line of sight to the Galactic center. We show that by focusing on high-magnication events, the probability of detecting planets of Jupiter mass or greater in the lensing zone is nearly 100%, with the probability remaining high down to [(0.61.6)R E ] Saturn masses and substantial even at 10 Earth masses. This high probability allows a nearly denitive statement to be made about the existence of lensing-zone planets in each such system that undergoes high magnication. One might expect light-curve deviations caused by the source passing near the small primary-lens caustic to be small because of the large distance of the perturbing planet, but this e ect is overcome by the high magnication. High-magnication events are relatively rare (e.g., D1/20 of events have peak magnications greater than 20), but they occur regularly, and the peak can be predicted in advance, allowing extrasolar planet detection with a relatively small use of resources over a relatively small amount of time.