Radio Activity from the Rapidly Rotating T dwarf 2MASS 2228-4310

Abstract: We present the detection of 2MASS J22282889-4310262 (2M2228), a T6/T6.5 brown dwarf, using the Karl G. Jansky Very Large Array (VLA) archival data observed at C band (4-8 GHz) over two observing epochs ($2\times96$ minutes). 2M2228 is detected at time and frequency averaged Stokes I and V peak flux densities of $67.3\pm4.9\ μ \rm{Jy beam}^{-1}$ and $14.4\pm3.0\ μ\text{Jy beam}^{-1}$ in the first epoch and $107.2\pm5.2\ μ\rm{Jy\ beam}^{-1}$ and $-20.7\pm1.2\ μ\text{Jy beam}^{-1}$ in the second epoch. This discovery constitutes the eighth and, notably, the most rapidly rotating T dwarf detected to date at radio wavelengths. Our observations reveal highly polarised bursts at fractional polarisation ratios $f_\text{c}>50$%. Using Stokes I light curves, we measure occurrence intervals of $\sim47$ and $\sim58$ minutes in the two observing epochs respectively with the first burst aligning within a half period timescale of the the previously measured mid infrared photometric period of $85.8\pm0.32$ minutes. We attribute the emission to the electron cyclotron maser emission (ECME) and constrain the magnetic field strength to $B\gtrsim1.4$ kG. We emphasise that the periods inferred are provisional considering the short observing durations. The combination of previously demonstrated atmospheric stability and newly detected radio emission in 2M2228 makes it a promising laboratory for testing magnetospheric currents-driven auroral models and for guiding future coordinated James Webb Space Telescope (JWST) and radio observations to probe the link between auroral activity and atmospheric dynamics in T-type brown dwarfs.