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

## TL;DR

This paper reports the discovery of a substellar companion near the planet/brown dwarf boundary via gravitational microlensing, with implications for understanding such objects at wide separations.

## Contribution

It presents a new microlensing detection of a companion near the planet/brown dwarf boundary at wide orbit, challenging previous claims of planetary companions in similar events.

## Key findings

- Companion mass estimated at ~8 Jupiter masses.
- Projected separation of about 10 AU from the host.
- The companion could be a high-mass planet or a low-mass brown dwarf.

## 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 $\approx8~M_{\rm Jup} (M_*/0.5M_\odot)$. Thus, the companion is either a high-mass giant planet or a low-mass brown dwarf, depending on the mass of the primary $M_*$. 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 $\approx10~{\rm a.u.}(M_*/0.5M_\odot)^{1/2}$ 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.