Resolving gravitational microlensing events with long-baseline optical interferometry. Prospects for the ESO Very Large Telescope Interferometer

TL;DR

Long-baseline optical interferometry, especially with the ESO VLT Interferometer, can resolve microlensed images, enabling precise measurements of lens masses and positions, which were previously ambiguous due to limited observational data.

Contribution

This paper demonstrates the potential of long-baseline interferometry, particularly the ESO VLT Interferometer, to resolve microlensing images and accurately determine physical parameters of the lenses.

Findings

Several tens of microlensing events could be observed annually.

Interferometry can measure angular separation of images, leading to direct mass and location determination.

The approach can resolve ambiguities in microlensing event interpretation.

Abstract

Until now, the detailed interpretation of the observed microlensing events has suffered from the fact that the physical parameters of the phenomenon cannot be uniquely determined from the available astronomical measurements, i.e. the photometric lightcurves. The situation will change in the near-future with the availability of long-baseline, sensitive optical interferometers, which should be able to resolve the images of the lensed objects into their components. For this, it will be necessary to achieve a milliarcsecond resolution on sources with typical magnitudes K $\ga 12$. Indeed, brighter events have never been observed up to now by micro-lensing surveys. We discuss the possibilities opened by the use of long baseline interferometry in general, and in particular for one such facility, the ESO VLT Interferometer, which will attain the required performance. We discuss the expected accuracy and limiting magnitude of such measurements. On the basis of the database of the events detected by the OGLE experiment, we estimate the number of microlenses that could be available for measurements by the VLTI. We find that at least several tens of events could be observed each year. In conjunction with the photometric data, our ability to measure the angular separation between the microlensed images will enable a direct and unambiguous determination of both their masses and locations.