Coffee talks
Monday 28/04/2025 @ 14:30, Sala riunioni quarto piano
Rick Perley (NRAO, Socorro NM USA), "Precision Meter-wavelength Polarimetry with the Very Large Array"
Accurate imaging polarimetry at meter wavelengths requires removal of the highly variable ionospheric Faraday rotation (IFRM) with an accuracy of 0.1 rad/m^2 or better. Models to estimate the VTEC using GNSS timing data, combined with global terrestrial magnetic field models have been developed over the past 25 years. Estimating the accuracy of these models requires observations of a source of known intrinsic electric vector position angle (EVPA) over a wide rage of ionospheric conditions. Using eight VLA polarimetric observations of the moon spanning ten years using the VLA's P-band (295 -- 445 MHz) receivers, we have tested the accuracy of seven global IONEX models produced by the AIPS program TECOR, and the regional model derived by ALBUS. All seven global models overestimate the IFRM, typically by 0.5 to 1.0 rad/m^2 -- a value which remains constant over many hours, including day -- night transitions. The 'ALBUS' model, which uses GNSS ground station data within ~300 km of the requested site, generates predictions which are always the closest -- usually with 0.2 rad/m^2 -- to the observed values.