Eclipsing negative-parity image of gravitational microlensing by a giant-lens star

Abstract: Gravitational Microlensing has been used as a powerful tool for astrophysical studies and exoplanet detections. In the gravitational microlensing, we have two images with negative and positive parities. The negative-parity image is a fainter image and is produced at a closer angular separation with respect to the lens star. In the case of a red-giant lens star and large impact parameter of lensing, this image can be eclipsed by the lens star. The result would be dimming the flux receiving from the combination of the source and the lens stars and the light curve resembles to an eclipsing binary system. In this work, we introduce this phenomenon and propose an observational procedure for detecting this eclipse. The follow-up microlensing telescopes with lucky imaging camera or space-based telescopes can produce high resolution images from the events with reddish sources and confirm the possibility of blending due to the lens star. After conforming a red-giant lens star and source star, we can use the advance photometric methods and detect the relative flux change during the eclipse in the order of $10^{-4}-10^{-3}$. Observation of the eclipse provides the angular size of source star in the unit of Einstein angle and combination of this observation with the parallax observation enable us to calculate the mass of lens star. Finally, we analyzed seven microlensing event and show the feasibility of observation of this effect in future observations.