Radio detections of ultracool dwarfs provide insight into their magnetic fields and the dynamos that maintain them , especially at the very bottom of the main sequence , where other activity indicators dramatically weaken .
Until recently , radio emission was only detected in the M and L dwarf regimes , but this has changed with the Arecibo detection of rapid polarized flares from the T6.5 dwarf 2MASS J10475385+2124234 .
Here , we report the detection of quasi-quiescent radio emission from this source at 5.8 GHz using the Karl G. Jansky Very Large Array .
The spectral luminosity is L _ { \nu } = ( 2.2 \pm 0.7 ) \times 10 ^ { 12 } erg s ^ { -1 } Hz ^ { -1 } , a factor of \sim 100 times fainter than the Arecibo flares .
Our detection is the lowest-luminosity yet achieved for an ultracool dwarf .
Although the emission is fully consistent with being steady , unpolarized , and broadband , we find tantalizing hints for variability .
We exclude the presence of short-duration flares as seen by Arecibo , although this is not unexpected given estimates of the duty cycle .
Follow-up observations of this object will offer the potential to constrain its rotation period , electron density , and the strength and configuration of the magnetic field .
Equally important , follow-up will address the question of whether the electron cyclotron maser instability , which is thought to produce the flares seen by Arecibo , also operates in the very different parameter regime of the emission we detect , or whether instead this ultracool dwarf exhibits both maser and gyrosynchrotron radiation , potentially originating from substantially different locations .