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We report upper limits to the radio and X-ray emission from the newlydiscovered ultracool dwarf binary WISE J104915.57$-$531906.1 (Luhman 16AB). Asthe nearest ultracool dwarf binary (2 pc), its proximity offers a heftyadvantage to studying plasma processes in ultracool dwarfs which are moresimilar in gross properties (radius, mass, temperature) to the solar systemgiant planets than stars. The radio and X-ray emission upper limits from theAustralia Telescope Compact Array (ATCA) and Chandra observations, eachspanning multiple rotation periods, provide the deepest fractional radio andX-ray luminosities to date on an ultracool dwarf, with $\log{(L_{\rmr,\nu}/L_{\rm bol}) [Hz^{-1}]} < -18.1$ (5.5 GHz), $\log{(L_{\rm r,\nu}/L_{\rmbol}) [Hz^{-1}]} < -17.9$ (9 GHz), and $\log{(L_{\rm x}/L_{\rm bol})} < -5.7$.While the radio upper limits alone do not allow for a constraint on themagnetic field strength, we limit the size of any coherently emitting region inour line of sight to less than 0.2\% of the radius of one of the brown dwarfs.Any source of incoherent emission must span less than about 20\% of the browndwarf radius, assuming magnetic field strengths of a few tens to a few hundredGauss. The fast rotation and large amplitude photometric variability exhibitedby the T dwarf in the Luhman 16AB system are not accompanied by enhancednonthermal radio emission, nor enhanced heating to coronal temperatures, asobserved on some higher mass ultracool dwarfs, confirming the expecteddecoupling of matter and magnetic field in cool neutral atmospheres.

The Deepest Constraints on Radio and X-ray Magnetic Activity in Ultracool Dwarfs from WISE J104915.57-531906.1