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15th of August 2023
Periodic radio emission from an ultracool brown dwarf
by Rose et al.
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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