Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event

Abstract

We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555. We measure the microlens parallax vector $\ddot{I}{€}_{\mathrm{E}}$ 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 $\ddot{I}{€}_{\mathrm{E}}$ determination with the angular Einstein radius $\hat{I}{¸}_{\mathrm{E}}$ measured by VLTI GRAVITY observations, we find that the lens is a star with mass $M_{\mathrm{L}}=0.495\pm 0.063M_{\odot }$ at a distance $D_{\mathrm{L}}=429\pm 21\mathrm{pc}$. We find that the blended light basically all comes from the lens. The lens-source proper motion is $\hat{I}{¼}_{\mathrm{rel},\mathrm{hel}}=26.55\pm 0.36\mathrm{mas}\mathrm{y}{\mathrm{r}}^{-1}$, so with currently available adaptive-optics (AO) 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.

3 Figures and 6 Tables Submitted to AAS Journal