ASKAP observations of multiple rapid scintillators reveal a degrees-long plasma filament. Issue 3 (21st January 2021)

• Record Type: Journal Article
• Authors: Wang, Yuanming; Tuntsov, Artem; Murphy, Tara; Lenc, Emil; Walker, Mark; Bannister, Keith; Kaplan, David L; Mahony, Elizabeth K
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 502:Issue 3(2021)
• Page Start: 3294
• Page End: 3311
• Publication Date: 2021-01-21
• Subjects: scattering -- techniques: image processing -- ISM: general -- radio continuum: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab139
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present the results from an Australian Square Kilometre Array Pathfinder search for radio variables on timescales of hours. We conducted an untargeted search over a 30 deg 2 field, with multiple 10-h observations separated by days to months, at a central frequency of 945 MHz. We discovered six rapid scintillators from 15-min model-subtracted images with sensitivity of $\sim\! 200\, \mu$ Jy/beam; two of them are extreme intra-hour variables with modulation indices up to $\sim 40{{\ \rm per\ cent}}$ and timescales as short as tens of minutes. 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. We derived kinematic models of this plasma from the annual modulation of the scintillation rate of our sources, and we estimated its likely physical properties: a distance of ∼4 pc and length of ∼0.1 pc. The characteristics we observe for the scattering screen are incompatible with published suggestions for the origin of intra-hour variability leading us 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.