MACHO Alert 95‐30: First Real‐Time Observation of Extended Source Effects in Gravitational Microlensing

Abstract

We present analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event toward the Galactic bulge whose peak magnication departs signicantly from the standard point-source microlensing model. Alert 95-30 was observed in real time by the Global Microlensing Alert Network (GMAN), which obtained densely sampled photometric and spectroscopic data throughout the event. We interpret the light-curve "" ne structure as indicating transit of the lens across the extended face of the source star. This signies resolution of a star several kiloparsecs distant.