Complete Parallax and Proper Motion Solutions For Halo Binary-Lens Microlensing Events
Abstract
A major problem in the interpretation of microlensing events is that the only measured quantity, the Einstein time scale t_E, is a degenerate combination of the three quantities one would like to know, the mass, distance, and speed of the lens. This degeneracy can be partly broken by measuring either a "parallax" or a "proper motion'' and completely broken by measuring both. Proper motions can easily be measured for caustic-crossing binary-lens events. Here we show that it is also possible to measure a parallax for some of these events by comparing the light curves of the caustic crossing as seen from two observatories on Earth. For Galactic halo binary lenses seen toward the LMC, the light curve is delayed by a seemingly minuscule 15 seconds (compared to t_E \~ 40 days). However, this is sufficient to cause a difference in magnification of order 10%. To actually extract complete parallax information (as opposed to merely detecting the effect) requires observations from three non-collinear observatories. The method can also be applied to bulge microlensing events and to Galactic halo binary lenses seen toward M31.Keywords
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