A theoretical calculation of microlensing signatures caused by free-floating planets towards the Galactic bulge

TL;DR

This paper provides a theoretical analysis of microlensing signatures caused by free-floating planets towards the Galactic bulge, predicting that the Euclid observatory could detect hundreds to thousands of such events monthly, including parallax effects.

Contribution

It offers a new theoretical framework for predicting microlensing event rates caused by free-floating planets with Euclid, incorporating recent mass function data and synthetic population simulations.

Findings

Euclid could detect hundreds to thousands of free-floating planet microlensing events per month.

Parallax effects in these events could be detected with about 30% efficiency.

The study estimates the optical depth and microlensing rate based on the latest free-floating planet mass function.

Abstract

Free-floating planets are recently drawing a special interest of the scientific community. Gravitational microlensing is up to now the exclusive method for the investigation of free-floating planets, including their spatial distribution function and mass function. In this work, we examine the possibility that the future Euclid space-based observatory may allow to discover a substantial number of microlensing events caused by free-floating planets. Based on latest results about the free-floating planet mass function in the mass range $[10^{-5}, 10^{-2}]M_{\odot}$, we calculate the optical depth towards the Galactic bulge as well as the expected microlensing rate and find that Euclid may be able to detect hundreds to thousands of these events per month. Making use of a synthetic population, we also investigate the possibility of detecting parallax effect in simulated microlensing events due to free-floating planets and find a significant efficiency for the parallax detection that turns out to be around 30%.