The astrometric signal of microlensing events caused by free floating planets

TL;DR

This paper explores how astrometric measurements of microlensing events caused by free floating planets can reveal physical parameters and estimates the detection potential of Gaia over five years.

Contribution

It analyzes the astrometric signals of microlensing by free floating planets and estimates Gaia's capability to detect such events.

Findings

Astrometric signals increase with higher FFP masses.

Approximately a dozen FFP microlensing events detectable by Gaia in five years.

Astrometric observations provide valuable information about FFPs.

Abstract

Astrometric observations of microlensing events can be used to obtain important information about lenses. During these events, the shift of the position of the multiple image centroid with respect to the source star location can be measured. This effect, which is expected to occur on scales from micro-arcseconds to milli-arcseconds, depends on the lens-source-observer system physical parameters. Here, we consider the astrometric and photometric observations by space and ground-based telescopes of microlensing events towards the Galactic bulge caused by free floating planets (FFPs). We show that the efficiency of astrometric signal on photometrically detected microlensing events tends to increase for higher FFP masses in our Galaxy. In addition, we estimate that during five years of the Gaia observations, about a dozen of microlensing events caused by FFPs are expected to be detectable.