Rick Perley (NRAO)

Abstract: The radio quasars 3C286 and 3C138 have long been used to determine the EVPAs of polarimetric imaging with the VLA. Since at least the 1960s, it has been ‘accepted wisdom’ that the correct EVPA of 3C286 is 33 degrees at all frequencies. However, recent VLA observations of the moon, Venus, and Mars have shown there are small, but significant deviations from the presumed 33 degrees, resulting in about a 10 degree spread between 1 and 50 GHz. Recent MeerKAT observations have confirmed this spread at their frequencies of overlap, and strongly suggest much larger deviations to lower values are seen below 1 GHz. However, accurate estimation of the EVPAs below ~1 GHz will require accurate corrections for ionospheric Faraday rotation, which are currently lacking.

The image above shows a contour map of 3C286 from a VLA observation at 8.4 GHz (from Akujor & Garrington 1995 ). The jet to the west of the core (i.e., to the right in this image) is highly polarized with E-vectors parallel to the jet axis at 8.4 GHz.