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Rose et al. 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. They detected this high
proper motion ultracool dwarf with the Australian SKA Pathfinder in
1.36 GHz imaging data from the Rapid ASKAP Continuum Survey. They
found WISE J062309.94−045624.6 to an average total flux density of ~4
mJy per beam, with an absolute circular polarization fraction of 66%.
In follow-up observations with the Australian Telescope Compact Array
and MeerKAT they identified a multi-peaked pulse structure, used
dynamic spectra to place a lower limit of 710 gauss on the dwarf’s
magnetic field, and measured a 1.9 hour periodicity which they
conclude is due to rotational modulation. The luminosity and
period 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. The figure above shows the
circular polarisation (Stokes V) dynamic spectrum (1.3–2.0 GHz) from
the ATCA observation. The lower panel shows the circular polarisation
(red) and total intensity (black) lightcurves. Both lightcurves and
the dynamic spectrum display a clear periodicity. (The total
intensity dynamic spectrum was not used as it is heavily affected by
artefacts from bright off-axis emission.) Horizontal gaps correspond
to frequencies that were flagged due to radio frequency interference
(RFI).
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