Quasi-Quiescent Radio Emission from the First Radio-Emitting T Dwarf

TL;DR

This paper reports the first detection of quasi-quiescent radio emission from a T dwarf, revealing insights into its magnetic activity and emission mechanisms, with implications for understanding ultracool dwarf magnetospheres.

Contribution

It presents the first detection of steady, low-luminosity radio emission from a T dwarf, expanding knowledge of magnetic activity in ultracool dwarfs beyond previous flare observations.

Findings

Detected steady radio emission at 5.8 GHz from a T dwarf

Emission is unpolarized and broadband, with hints of variability

No short-duration flares were observed in this detection

Abstract

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 luminosity is {\nu}L_{\nu} = (1.3 +- 0.4) x 10^22 erg/s, a factor of ~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.