A systematic fitting scheme for caustic-crossing microlensing events

Kains, N.; Cassan, A.; Horne, K.; Albrow, M. D.; Dieters, S.; Fouqué, P.; Greenhill, J.; Udalski, A.; Zub, M.; Bennett, D. P.; Dominik, M.; Donatowicz, J.; Kubas, D.; Tsapras, Y.; Anguita, T.; Batista, V.; Beaulieu, J.-P.; Brillant, S.; Bode, M.; Bramich, D. M.; Burgdorf, M.; Caldwell, J. A. R.; Cook, K. H.; Coutures, Ch.; Dominis Prester, D.; Jørgensen, U. G.; Kane, S.; Marquette, J. B.; Martin, R.; Menzies, J.; Pollard, K. R.; Rattenbury, N.; Sahu, K. C.; Snodgrass, C.; Steele, I.; Vinter, C.; Wambsganss, J.; Williams, A.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Szewczyk, O.; Szymański, M. K.; Ulaczyk, K. and Wyrzykowski, Ł. (2009). A systematic fitting scheme for caustic-crossing microlensing events. Monthly Notices of the Royal Astronomical Society, 395(2) pp. 787–796.

DOI: https://doi.org/10.1111/j.1365-2966.2009.14615.x

Abstract

We outline a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parametrization proposed and detailed by Cassan. 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-χ2 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 event.

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