Simulating Gravitational Microlensing Events by TESS: Predictions on Statistics and Properties

TL;DR

This study uses Monte Carlo simulations to predict the number, properties, and detection efficiency of gravitational microlensing events observable by TESS, focusing on different star samples and lens masses.

Contribution

It provides the first detailed predictions of TESS's microlensing event statistics, including detection efficiencies and the influence of finite-source and parallax effects.

Findings

Average microlensing optical depth for CTL stars: 0.2×10^{-9}

Event rate for CTL stars: 0.6×10^{-9} per star per day

Detection efficiency peaks for super-Earth to Jupiter-mass free-floating planets

Abstract

We study the statistics and properties of microlensing events that can be detected by the Transiting Exoplanet Survey Satellite(TESS) based on Monte Carlo simulations. We simulate potential microlensing events from a sample of the TESS Candidate Target List(CTL) stars by assuming different observational time spans(or different numbers of sectors for each star) and a wide range of lens masses, i.e., $M_{\rm l}\in [0.1M_{\oplus},~2 M_{\odot}]$. On average, the microlensing optical depth and the event rate for CTL stars are $\simeq 0.2\times 10^{-9}$, and $\Gamma_{\rm{TESS}}\simeq0.6\times10^{-9}$ per star per day, respectively. The microlensing optical depth decreases by increasing the CTL priority, whereas the efficiency for detecting their microlensing signals enhances with the priority. Additionally, we simulate the microlensing events from the TESS Full-Frame Images(FFIs) stars extracted from the \texttt{TESS}-\texttt{SPOC} pipeline. The optical depth and event rate for these stars are on average $\simeq 1$-$3\times 10^{-9}$, and $\Gamma_{\rm{TESS}}\simeq 1$-$4\times 10^{-9}$ per star per day, and their highest values occur for sector $12$. The total number of microlensing events for the CTL stars is $N_{\rm e, \rm{tot}}\sim0.03$, whereas for the FFIs' stars number of events per star during $27.4$-day observing windows is $\hat{N}_{\rm e, \rm{tot}}\simeq1.4 \times 10^{-6}$. Based on four criteria we extract the detectable microlensing events and evaluate the detection efficiencies. The highest efficiency for detecting microlensing events from the TESS data occurs for the lens mass $\log_{10}[M_{\rm l}(M_{\odot})] \in [-4.5$,~$-2.5]$, i.e., super-Earth to Jupiter-mass Free Floating Planets(FFPs). The detectable microlensing events from the TESS stars are significantly affected by both finite-source and parallax effects.