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28th of November 2022
A Radio Variable in the Tenth Deeper, Wider, Faster Observing Run
by Dobie et al.
The Deeper, Wider, Faster (DWF) program coordinates simultaneous observations between telescopes across the entire electromagnetic spectrum to study astrophysical transients on timescales of milliseconds to days. The tenth DWF observing run was carried out in September 2021 and consisted of six consecutive days of observations with ASKAP, the Dark Energy Camera, the Hard X-ray Modulation Telescope and the Parkes 64m “Murriyang” radio telescope. Dobie et al. present the results of an image-domain search for transient, variable and circularly polarised sources carried out with ASKAP using data from the observing run. One of the variable sources detected was SCR J1845–6357, a nearby binary system. The figure above shows the intra-observation light curve, with the data avergaed into 15-minute samples, demonstrating that the variability stems from a series of pulses, each lasting ∼2 h. The shaded region denotes the duration of the simultaneous Swift observation, in which no X-ray or UV emission was detected, suggesting that previously observed X-ray variability and radio activity are not coupled. The radio emission is highly (∼90%) circularly polarised during the pulses, but not in the quiescent state. An optical period of 14.1±0.2 h was measured for SCR J1845–6357 from NASA's Transiting Exoplanet Survey Satellite (TESS), and the flares detected in the ASKAP data are consistent with this periodicity. The team conclude that the observed radio variability stems from rotational modulation, making this the slowest rotating radio-pulsing ultra-cool dwarf discovered to-date.

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