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

We present the discovery of a substellar companion to the primary host lens in the microlensing event <ASTROBJ>MOA-2012-BLG-006</ASTROBJ>. The companion-to-host mass ratio is 0.016, corresponding to a companion mass of ≈8 M<SUB>Jup</SUB>(M<SUB>∗</SUB>/ 0.5 M<SUB>⊙</SUB>). Thus, the companion is either a high-mass giant planet or a low-mass brown dwarf, depending on the mass of the primary M<SUB>∗</SUB>. 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(M<SUB>∗</SUB>/ 0.5 M<SUB>⊙</SUB>)<SUP>1 / 2</SUP> 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.