A companion on the planet/brown dwarf mass boundary on a wide orbit discovered by gravitational microlensing

Abstract

We present the discovery of a substellar companion to the primary host lens in the microlensing event MOA-2012-BLG-006. The companion-to-host mass ratio is 0.016, corresponding to a companion mass of ≠8 MJup(Mâ-/0.5 MâŠ(tm)). Thus, the companion is either a high-mass giant planet or a low-mass brown dwarf, depending on the mass of the primary Mâ-. The companion signal was separated from the peak of the primary event by a time that was as much as four times longer than the event timescale. We therefore infer a relatively large projected separation of the companion from its host of ≠10 au(Mâ-/0.5 MâŠ(tm))1/2 for a wide range (3-7 kpc) of host star distances from the Earth. We also challenge a previous claim of a planetary companion to the lens star in microlensing event OGLE-2002-BLG-045.