A MeerKAT polarization survey of southern calibration sources
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Date
2024
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Abstract
We report on full-Stokes L-band observations of 98 MeerKAT calibration sources. Linear polarization is detected in 71
objects above a fractional level of 0.2%. We identify ten sources with strong fractional linear polarization and low
Faraday rotation measure that could be suitable for wide-band absolute polarization calibration. We detect significant
circular polarization from 24% of the sample down to a detection level of 0.07%. Circularly polarized emission is seen
only for flat spectrum sources α>−0.5. We compare our polarized intensities and Faraday synthesis results to data from
the NVSS at 1400 MHz and the ATCA SPASS survey at 2300 MHz. NVSS data exist for 54 of our sources and SPASS
data for 20 sources. The percent polarization and rotation measures from both surveys agree well with our results. The
residual instrumental linear polarization for these observations is measured at 0.16%, and the residual instrumental circular
polarization is measured at 0.05%. These levels may reflect either instabilities in the relative bandpass between the two
polarization channels with either time or antenna orientation, or atmospheric/ionospheric variations with pointing
direction. Tracking of the hourly gain solutions on J0408-6545 after transfer of the primary gain solutions suggests a
deterioration of the gain stability by a factor of several starting about 2 hr after sunrise. This suggests that observing
during the nighttime could dramatically improve the precision of polarization calibration.