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Simulations of Gravitational Microlensing

Penny, Matthew Thomas

[Thesis]. Manchester, UK: The University of Manchester; 2011.

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Abstract

Gravitational microlensing occurs when a massive lens (typically a star) deflects lightfrom a more distant source, creating two unresolvable images that are magnified. Theeffect is transient due to the motions of the lens and source, and the changing magnificationgives rise to a characteristic lightcurve. If the lensing object is a binary star orplanetary system, more images are created and the lightcurve becomes more complicated.Detection of these lightcurve features allows the lens companion’s presence tobe inferred.Orbital motion of the binary lens can be detected in some microlensing events,but the expected fraction of events which show orbital motion has not been knownpreviously. We use simulations of orbiting-lens microlensing events to determine thefraction of binary-lens events that are expected to show orbital motion. We also usethe simulations to investigate the factors that affect this detectability.Following the discovery of some rapidly-rotating lenses in the simulations, we investigatethe conditions necessary to detect lenses that undergo a complete orbit duringa microlensing event. We find that such events are detectable and that they should occurat a low but detectable rate. We also derive approximate expressions to estimate thelens parameters, including the period, from the lightcurve. Measurement of the orbitalperiod can in some cases allow the lens mass to be measured.Finally we develop a comprehensive microlensing simulator, MaBμLS, that usesthe output of the Besanc¸on Galaxy model to produce synthetic images of Galactic starfields.Microlensing events are added to the images and photometry of their lightcurvessimulated. We apply these simulations to a proposed microlensing survey by the Euclidspace mission to estimate its planet detection yield.