COLLOQUIUM JEROEN STIL, University of Calgary

Effects of Turbulent Near-Source Plasma on the Scatter in Surveys of Faraday Rotation Measure OR The Trouble with Tribble

Faraday rotation of linearly polarized radio waves in a magnetized plasma has been, for decades, the foremost important observational probe of cosmic magnetic fields from kiloparsec to megaparsec scales.  The Rotation Measure Grid, a list of (mostly) extragalactic sources with measured Faraday rotation, is the starting point for much of the science from large polarization surveys with radio interferometers, including the Square Kilometre Array. With the attainable bandwidth of order 1 GHz in L-band, measurement errors of Rotation Measure (RM) are of the order of 1 rad/m2, much smaller than the scatter imposed by many astrophysical plasmas. Faraday rotation of a turbulent plasma with structures on a range of scales that are smaller than the beam, imposes not only depolarization, but also scatter in Rotation Measure, referred to as RM jitter. This RM jitter is a form of scatter in the RM grid that depends on the amplitude and slope of the power spectrum of structure in the plasma, but also on the observed wavelength range. Models of this kind can reproduce higher RM scatter for sources that are less polarized, as recently observed in the POSSUM survey by Vanderwoude et al. (2024). They also provide a new framework for the interpretation of polarimetry of radio sources over bandwidths of a few GHz, for example when combining data from the THOR and GLOSTAR surveys. New? Such models were already examined by Tribble (1991)!

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https://uni-hamburg.zoom.us/j/66006535328?pwd=aGkrSjJIYmZjK0VpYlpGL0ZrdHg2UT09