摘要：We analyze the microlensing event OGLE-2011-BLG-0173, which shows a small perturbation at the end of themicrolensing event caused by the primary lens. We consider both binary lens and binary source models andexplore their degeneracies, some of which have not previously been recognized. There are two families of binarylens solutions, one with a mass ratio q≈4×10 −4 and a separation s≈4.6, and the other with q≈0.015 ands≈0.22, i.e., both have companions in the planetary regime. We search for solutions by using Bayesian analysisthat includes planet frequency as a prior and find that the s≈4.6 family is the preferred one with a M 4 Uranus»planet on an orbit of ∼10au. The degeneracies arise from a paucity of information on the anomaly, demonstratingthat high-cadence observations are essential for characterizing wide-orbit microlensing planets. Hence, we predictthat the planned Wide-Field Infrared Survey Telescope microlensing survey will be less prone to thesedegeneracies than the ongoing ground-based surveys. We discuss the known low-mass, wide-orbit companions andnotice that for the largest projected separations the mass ratios are either high (consistent with brown dwarfcompanions) or low (consistent with Uranus analogs), but intermediate mass ratios (Jupiter analogs on wide orbits)have not been detected to date, despite the fact that the sensitivity to such planets should be higher than that ofUranus analogs. This is therefore tentative evidence of the existence of a massive ice giant desert at wideseparations. On the other hand, given their low intrinsic detection sensitivity, Uranus analogs may be ubiquitous.
关键词：brown dwarfs;gravitational lensing: micro;planets and satellites: detection
