Binary microlensing by high eccentric stellar-mass black hole binaries

Abstract: Microlensing is one of the most promising tools for discovering stellar-mass black holes (BHs) in the Milky Way because it allows us to probe dark or faint celestial compact objects. While the existence of stellar-mass BHs has been confirmed through observation of X-ray binaries within our galaxy and gravitational waves from extragalactic BH binaries, a conclusive observation of microlensing events caused by Galactic BH binaries has yet to be achieved. In this study, we focus on those with high eccentricity, including unbound orbits, which can dynamically form in star clusters and could potentially increase the observation rate. We demonstrate parameter estimation for simulated light curves supposing various orbital configurations of BH binary lenses. We employ a model-based fitting using the Nelder-Mead method and Bayesian inference based on the Markov chain Monte Carlo method for the demonstration. The results show that we can retrieve true values of the parameters of high eccentric BH binary lenses within the 1$\sigma$ uncertainty of inferred values. We conclude it is feasible to find high eccentric Galactic BH binaries from the observation of binary microlensing events.