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9th of February 2021
ASKAP observations of reveal a degrees-long plasma filament
by Y-M Wang et al.
Wang et al. present the results from an ASKAP search for radio sources that vary on timescales of hours. They conducted an untargeted search over a 30 square degree field, with multiple observations at 945 MHz separated by days to months. The search discovered six rapid scintillators -- two of them are extreme intra-hour variables with timescales as short as tens of minutes. Just as visible light is distorted as it passes through our atmosphere to give stars their twinkle, when radio waves pass through matter, it also affects their brightness. Five of the variables are in a linear arrangement on the sky with angular width ∼1 arcmin and length ∼2 degrees, revealing the existence of a huge plasma filament in front of them. The filament is about a trillion kilometres long and 10 billion kilometres wide but only weighing about the mass of our Moon. These characteristics for the scattering screen are incompatible with published suggestions for the origin of intra-hour variability leading the team to propose a new picture in which the underlying phenomenon is a cold tidal stream. This is the first time that multiple scintillators have been detected behind the same plasma screen, giving direct insight into the geometry of the scattering medium responsible for enhanced scintillation. The results are presented in a paper published in Monthly Notices of the Royal Astronomical Society. The image above shows an artist's impression of the thin gas filament, which may have been caused by tidal disruption by a star. (Image credit: Mark Myers/OzGrav)

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