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 archival data observed at C band (4–8 GHz) over two observing epochs ($2\times 96$ min). 2M2228 is detected at time and frequency averaged Stokes I and V peak flux densities of $67.3\pm 4.9$ and ${14.4\pm 3.0\ \mu \text{Jy beam}^{-1}}$ in the first epoch and $107.2\pm 5.2$ and ${-20.7\pm 1.2\ \mu \text{Jy beam}^{-1}}$ 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 polarized bursts at fractional polarization ratios $f_\text{c}>50$ per cent. Using Stokes I light curves, we measure occurrence intervals of ${\sim} 47$ and $58$ min in the two observing epochs, respectively, with the first burst aligning within a half-period time-scale of the the previously measured mid-infrared photometric period of $85.8\pm 0.32$ min. We attribute the emission to the electron cyclotron maser emission and constrain the magnetic field strength to $B\gtrsim 1.4$ kG. We emphasize 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. Future coordinated James Webb Space Telescope and radio observations will further probe the link between auroral activity and atmospheric dynamics in this brown dwarf.