The detection of radio emission from known X-ray flaring star EXO 040830−7134.7

Driessen, L. N.; Williams, D. R. A.; McDonald, I.; Stappers, B. W.; Buckley, D. A. H.; Fender, R. P. and Woudt, P. A. (2021). The detection of radio emission from known X-ray flaring star EXO 040830−7134.7. Monthly Notices of the Royal Astronomical Society (Early Access).



We report the detection of radio emission from the known X-ray flaring star EXO 040830−7134.7 during MeerKAT observations of the nearby cataclysmic variable VW Hydri. We have three epochs of MeerKAT observations, where the star is not detected in the first epoch, is detected in the second epoch, and is marginally detected in the third epoch. We cannot distinguish whether the detection is quiescent emission or a transient radio burst. If we assume the radio detection is quiescent emission the source lies somewhat to the right of the Güdel–Benz relation; however, if we assume the upper-limit on the radio non-detection is indicative of the quiescent emission then the source lies directly on the relation. Both cases are broadly consistent with the relation. We use archival spectral energy distribution data and new SALT high-resolution spectroscopy to confirm that EXO 040830−7134.7 is a chromospherically active M-dwarf with a temperature of 4000 ± 200 K of spectral type M0V. We use ASAS, ASAS-SN and TESS optical photometry to derive an improved rotational period of 5.18±0.04 days. This is the first radio detection of the source, and the first MeerKAT detection of an M-dwarf.

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