2017MNRAS.466.4211G

We present multi-epoch astrometric observations of the M9 ultracool dwarf TVLM513-46546 that is placed at the brown dwarf boundary. The new observations have been performed with the European Very Large Baseline Interferometry Network at 6 cm band. The target has been detected at seven epochs spanning three years, with measured quiescent emission flux in the range 180-300 µJy. We identified four short-duration flaring events (0.5-2 mJy) with very high circular polarization (∼75 per cent-100 per cent). Properties of the observed radio flares support the physical model of the source that is characterized by the electron cyclotron maser instability responsible for outbursts of radio emission. Combined with Very Long Baseline Array earlier data, our detections make it possible to refine the absolute parallax π=93.27^+0.18_–0.17 mas. Our measurements rule out TVLM513-46546 companions more massive than Jupiter in orbits with periods longer than ∼1 yr.