Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event
Weicheng Zang, Subo Dong, Andrew Gould, Sebastiano Calchi Novati, Ping Chen, Hongjing Yang, Shun-Sheng Li, Shude Mao, K. B. Alton, J. Brimacombe, Sean Carey, G. W. Christie, F. Delplancke-Ströbele, Dax L. Feliz, B. Scott Gaudi, J. Green, Shaoming Hu, T. Jayasinghe, R. A. Koff, A. Kurtenkov, A. Mérand, Milen Minev, Robert Mutel, T. Natusch, Tyler Roth, Yossi Shvartzvald, Fengwu Sun, T. Vanmunster, Wei Zhu
Abstract
Abstract We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555 (Kojima-1). We measure the microlens parallax vector using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this determination with the angular Einstein radius measured by VLTI-GRAVITY observations, we find that the lens is a star with mass at a distance D L = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is , so with currently available adaptive-optics instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite-parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.