Binary Microlensing Event MACHO-98-SMC-1

Abstract

The recent binary microlensing event toward the Small Magellanic Cloud MACHO-98-SMC-1 was alerted by the MACHO collaboration and monitored by many microlensing experiments for its complete coverage of the second caustic crossing. The purpose of this global monitoring campaign was to determine the relative proper motion $|\vecμ|$ of the lensing object with respect to the source star that may be indicative of the location of the lensing object. (``Is it a Galactic halo object or not, that is the question.") The estimated value $|\vecμ| \approx 1.3 km/(s \kpc)$ indicates that the binarylensing object belongs to the stellar population of the SMC. We discuss the implication of this binary event for the halo dark matter.