  Radio detection provides unique means to measure and study magnetic fields of
the coolest brown dwarfs. Previous radio surveys have observed quiescent and
flaring emission from brown dwarfs down to spectral type L3.5, but only upper
limits have been established for even cooler objects. We report the detection
of sporadic, circularly polarized flares from the T6.5 dwarf, 2MASS J1047+21,
with the Arecibo radio telescope at 4.75 GHz. This is by far the coolest brown
dwarf yet detected at radio frequencies. The fact that such an object is
capable of generating observable, coherent radio emission, despite its very
low, ~900 K temperature, demonstrates the feasibility of studies of brown
dwarfs in the meagerly explored LTY spectral range, using radio detection as a
tool.
