Radio Emission and Orbital Motion from the Close-Encounter Star-Brown\n Dwarf Binary WISE J072003.20-084651.2

We report the detection of radio emission and orbital motion from the nearby\nstar-brown dwarf binary WISE J072003.20-084651.2AB. Radio observations across\nthe 4.5-6.5 GHz band with the Very Large Array identify at the position of the\nsystem quiescent emission with a flux density of 15$\\pm$3 $\\mu$Jy, and a\nhighly-polarized radio source that underwent a 2-3 min burst with peak flux\ndensity 300$\\pm$90 $\\mu$Jy. The latter emission is likely a low-level magnetic\nflare similar to optical flares previously observed for this source. No\noutbursts were detected in separate narrow-band H$\\alpha$ monitoring\nobservations. We report new high-resolution imaging and spectroscopic\nobservations that confirm the presence of a co-moving T5.5 secondary and\nprovide the first indications of three-dimensional orbital motion. We used\nthese data to revise our estimates for the orbital period (4.1$^{+2.7}_{-1.3}$\nyr) and tightly constrain the orbital inclination to be nearly edge-on\n(93.6\\deg$^{+1.6\\deg}_{-1.4\\deg}$), although robust measures of the component\nand system masses will require further monitoring. The inferred orbital motion\ndoes not change the high likelihood that this radio-emitting very low-mass\nbinary made a close pass to the Sun in the past 100 kyr.\n