Precision Meter-wavelength Polarimetry with the Jansky Very Large Array

Abstract:
Accurate polarimetry at meter-wavelengths requires correction of the ionospheric Faraday rotation measure (IFRM) with an accuracy better than 0.15 rad/m².  In this talk I will show the results of testing of both global and regional estimates of the IFRM generated from GNSS timing data.   These tests used extensive polarimetric observations by the VLA and MeerKAT of the Moon, the only source of polarized emission with an a priori known electric vector position angle distribution.

We find that all global estimates made from maps of the vertical total electron content (VTEC) by various agencies overestimate the IFRM for VLA observations by 0.3 to 1.0 rad/m², while a regional model, utilizing GNSS data from stations near the VLA is much better, with errors of typically 0.15 rad/m².  This is sufficiently accurate for VLA observations at 300 MHz, but not for lower frequencies.  

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