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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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