  We present the results of a 4.75 GHz survey of 33 brown dwarfs and one young
exoplanetary system for flaring radio emission, conducted with the 305-m
Arecibo radio telescope. The goal of this program was to detect and
characterize the magnetic fields of objects cooler than spectral type L3.5, the
coolest brown dwarf detected prior to our survey. We have also attempted to
detect flaring radio emission from the HR 8799 planetary system, guided by
theoretical work indicating that hot, massive exoplanets may have strong
magnetic fields capable of generating radio emission at GHz frequencies. We
have detected and confirmed radio flares from the T6.5 dwarf 2MASS
J10475385+2124234. This detection dramatically extends the temperature range
over which brown dwarfs appear to be at least sporadic radio-emitters, from
~1900 K (L3.5) down to ~900 K (T6.5). It also demonstrates that the utility of
radio detection as a unique tool to study the magnetic fields of substellar
objects extends to the coolest dwarfs, and, plausibly to hot, massive
exoplanets. We have also identified a single, 3.6 sigma flare from the L1
dwarf, 2MASS J1439284+192915. This detection is tentative and requires
confirmation by additional monitoring observations.
