Observations of Microlensed Images with Dual-field Interferometry: On-sky Demonstration and Prospects

TL;DR

This paper demonstrates the first successful interferometric observation of a microlensing event using GRAVITY Wide, enabling precise measurements of lens properties and opening new avenues for studying isolated compact objects.

Contribution

It presents the first on-sky demonstration of microlensed image resolution with GRAVITY Wide, significantly expanding the range of observable microlensing events and improving mass and distance measurements.

Findings

Resolved microlensed images in OGLE-2023-BLG-0061/KMT-2023-BLG-0496

Measured the angular Einstein radius with subpercent precision

Determined lens mass and distance with high accuracy

Abstract

Interferometric observations of gravitational microlensing events offer an opportunity for precise, efficient, and direct mass and distance measurements of lensing objects, especially those of isolated neutron stars and black holes. However, such observations have previously been possible for only a handful of extremely bright events. The recent development of a dual-field interferometer, GRAVITY Wide, has made it possible to reach out to significantly fainter objects and increase the pool of microlensing events amenable to interferometric observations by two orders of magnitude. Here, we present the first successful observation of a microlensing event with GRAVITY Wide and the resolution of microlensed images in the event OGLE-2023-BLG-0061/KMT-2023-BLG-0496. We measure the angular Einstein radius of the lens with subpercent precision, $\theta_{\rm E} = 1.280 \pm 0.009$ mas. Combined with the microlensing parallax detected from the event light curve, the mass and distance to the lens are found to be $0.472 \pm 0.012\,M_{\odot}$ and $1.81 \pm 0.05$ kpc, respectively. We present the procedure for the selection of targets for interferometric observations and discuss possible systematic effects affecting GRAVITY Wide data. This detection demonstrates the capabilities of the new instrument, and it opens up completely new possibilities for the follow-up of microlensing events and future routine discoveries of isolated neutron stars and black holes.