DO MICROLENSING EVENTS REPEAT?

摘要

For the purposes of gravitational microlensing, it is useful to define " close" binary lenses to be those that generate light curves having a single region of observable magnification; typically, the components of such a lens are separated by ～ 1-4 R_E. Microlensing by such close binary systems has already been observed. Wide binaries-i.e., those that can give rise to light curves with separate, disconnected regions of magnification and that have larger separations-are more common than close ones. Because the associated light curves can include two separate regions of magnification, there may appear to be a " repetition." In this paper we quantify our expectations of the frequency and characteristics of microlensing events that appear to repeat because the lens is a wide-binary system. We also point out that lensing by wide binaries provides a promising channel for the discovery of planetary systems. We find that roughly 0.5%-2% of observed microlensing events may exhibit apparent repetition because the lens is a wide binary. Lensing by wide binaries is therefore likely to be observed in the data collected by the present generation of microlensing experiments. We derive likely distributions of properties. We find that, for most events, one of the two regions of magnification has a maximum amplification that is smaller than that required for detection of a single point-mass lens. Yet because such light curves exhibit a region of more significant magnification, they can, in principle, be well studied. If such a study can lead to reliable methods to detect the second, less obvious region of magnification, it may also provide insight into the best ways to definitively identify lensing by low-mass single lenses.