A systematic fitting scheme for caustic-crossing microlensing events

TL;DR

This paper presents a new systematic method for fitting caustic-crossing microlensing events, improving the identification of multiple models and their physical properties through extensive parameter space exploration.

Contribution

The authors introduce a novel fitting scheme based on an alternative parameterisation, enhancing the ability to find multiple solutions in complex microlensing events.

Findings

Multiple low-chi2 solutions identified for OGLE-2007-BLG-472

The method uncovers minima difficult to detect with previous strategies

Physical properties of the models are estimated successfully

Abstract

We outline a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parameterisation proposed and detailed in Cassan (2008). As an illustration of our methodology, we present an analysis of OGLE-2007-BLG-472, a double-peaked Galactic microlensing event with a source crossing the whole caustic structure in less than three days. In order to identify all possible models we conduct an extensive search of the parameter space, followed by a refinement of the parameters with a Markov Chain-Monte Carlo algorithm. We find a number of low-chi2 regions in the parameter space, which lead to several distinct competitive best models. We examine the parameters for each of them, and estimate their physical properties. We find that our fitting strategy locates several minima that are difficult to find with other modelling strategies and is therefore a more appropriate method to fit this type of events.