Periodic Radio Emission from the T8 Dwarf WISE J062309.94-045624.6

TL;DR

This paper reports the first detection of periodic, circularly polarized radio emission from a T8 dwarf, revealing insights into its magnetic field and rotational properties, and suggesting future surveys could find more such ultracool objects.

Contribution

It presents the first detection of radio emission from a T8 dwarf, including measurements of its magnetic field, rotation period, and polarization, expanding understanding of ultracool dwarf magnetism.

Findings

Detected circularly polarized radio emission from WISE J062309.94-045624.6

Measured a rotation period of approximately 1.912 hours

Placed a lower limit of 0.71 kG on the magnetic field strength

Abstract

We present the detection of rotationally modulated, circularly polarized radio emission from the T8 brown dwarf WISE J062309.94-045624.6 between 0.9 and 2.0 GHz. We detected this high proper motion ultracool dwarf with the Australian SKA Pathfinder in $1.36$ GHz imaging data from the Rapid ASKAP Continuum Survey. We observed WISE J062309.94-045624.6 to have a time and frequency averaged Stokes I flux density of $4.17\pm0.41$ mJy beam$^{-1}$, with an absolute circular polarization fraction of $66.3\pm9.0\%$, and calculated a specific radio luminosity of $L_{\nu}\sim10^{14.8}$ erg s$^{-1}$ Hz$^{-1}$. In follow-up observations with the Australian Telescope Compact Array and MeerKAT we identified a multi-peaked pulse structure, used dynamic spectra to place a lower limit of $B>0.71$ kG on the dwarf's magnetic field, and measured a $P=1.912\pm0.005$ h periodicity which we concluded to be due to rotational modulation. The luminosity and period we measured are comparable to those of other ultracool dwarfs observed at radio wavelengths. This implies that future megahertz to gigahertz surveys, with increased cadence and improved sensitivity, are likely to detect similar or later-type dwarfs. Our detection of WISE J062309.94-045624.6 makes this dwarf the coolest and latest-type star observed to produce radio emission.