Integrated Polarization Properties of 3C48, 3C138, 3C147, and 3C286

TL;DR

This study analyzes the polarization properties of four key radio sources over 30 years, providing updated calibration data for radio astronomy and revealing slow, correlated polarization variations.

Contribution

It offers new long-term polarization measurements and frequency-dependent position angles for four calibration sources used in radio interferometry.

Findings

3C286's position angle increases from 33° to 36° between 8 and 45 GHz.

Fractional polarization of 3C286 is slowly rising at ~0.015% per year.

Polarization variations in other sources are correlated with flux density changes.

Abstract

We present the integrated polarization properties of the four compact radio sources 3C48, 3C138, 3C147 and 3C286, from 1 to 50 GHz, over a 30-year time frame spanning 1982 to 2012. These four sources are commonly used as flux density and polarization calibrators for cm-wave interferometers. Using the polarized emission of Mars, we have determined that the true position angle of the linearly polarized emission of 3C286 rises from 33 degrees at 8 GHz to 36 degrees at 45 GHz. There is no evidence for a change in the position angle over time. Using these values, the position angles of the intergrated polarized emission from the other sources are determined as a function of frequency and time. The fractional polarization of 3C286 is found to be slowly rising, at all frequencies, at a rate of ~0.015%/year. The fractional polarizations of 3C48, 3C138, and 3C147 are all slowly variable, with the variations clearly correlated with changes in the total flux densities of these sources.