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

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 ± 0.41 mJy beam−1, with an absolute circular polarization fraction of 66.3% ± 9.0%, and calculated a specific radio luminosity of L ν ∼ 1014.8 erg s−1 Hz−1. In follow-up observations with the Australian Telescope Compact Array and MeerKAT we identified a multipeaked 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 ± 0.005 hr 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.