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Radio Flaring from the T6 Dwarf WISEPC J112254.73+255021.5 with A Possible Ultra-short Periodicity

We present new results from a continuing 5 GHz search for flaring radio emission from a sample of L and T brown dwarfs, conducted with the 305-m Arecibo radio telescope. In addition to the previously reported flaring from the T6.5-dwarf 2MASS J10475385+212423, we have detected and confirmed circularly polarized flares from another T6-dwarf, WISEPC J112254.73+255021.5. Although the flares are sporadic, they appear to occur at a stable period of 0.288 hours. Given the current constraints, periods equal to its second and third subharmonic cannot be ruled out. The stability of this period over the 8-month timespan of observations indicates that, if real, it likely reflects the star's rapid rotation. If confirmed, any of the three inferred periodicities would be much shorter than the shortest, 1.41-hour rotation period of a brown dwarf measured so far. This finding would place a new observational constraint on the angular momentum evolution and rotational stability of substellar objects. The detection of radio emission from the sixth ~1000 K dwarf further demonstrates that the coolest brown dwarfs and, possibly, young giant planets, can be efficiently investigated using radio observations at centimeter wavelengths as a tool.