Variable and polarized radio emission from the T6 brown dwarf WISEP J112254.73+255021.5

TL;DR

This study investigates radio emissions from the T6 brown dwarf WISEP J112254.73+255021.5, finding variable polarized signals and questioning previous claims of ultra-short rotation periods, suggesting complex magnetic field geometry.

Contribution

The paper provides new observational data on radio polarization and variability, challenging prior rotation period estimates and revealing unique polarization behavior in a brown dwarf.

Findings

Detected variable, highly circularly polarized radio emission.

Observed potential periodicity of approximately 116 minutes.

First report of polarization handedness changing over time in such objects.

Abstract

Route & Wolszczan (2016) recently detected five radio bursts from the T6 dwarf WISEP J112254.73+255021.5 and used the timing of these events to propose that this object rotates with an ultra-short period of ~17.3 minutes. We conducted follow-up observations with the Very Large Array and Gemini-North but found no evidence for this periodicity. We do, however, observe variable, highly circularly polarized radio emission possibly with a period of 116 minutes, although our observation lasted only 162 minutes and so more data are needed to confirm it. Our proposed periodicity is typical of other radio-active ultracool dwarfs. The handedness of the circular polarization alternates with time and there is no evidence for any unpolarized emission component, the first time such a phenomenology has been observed in radio studies of very low-mass stars and brown dwarfs. We suggest that the object's magnetic dipole axis may be highly misaligned relative to its rotation axis.