vla_polcal

Polarization calibration pipeline for VLA continuum visibilities

This version requires the calibration outputs from the NRAO VLA pipeline to be present in the working directory, in order to un-do the parallactic angle correction done by the pipeline. The pipeline also takes into account the recent flaring of 3C147, and fits a polynomial to the flux density and polarization angle of known polarization calibrators.

Operations:

• (optional) Reverts the parallactic angle correction applied by the NRAO vla pipeline
• (optional) Performs gain calibration on the leakage calibrator (useful for resolved sources)
• Performs statistical outlier flagging on cross-hands
• Least-squares fitting of total flux, polarization fraction, and polarization angle using nth order polynomials for polarization angle calibrator
• Sets the frequency-dependent flux density scale of leakage and angle calibrators
• Calibrates the (per-baseband) cross-hand delays
• Calibrates the (per-baseband) leakage
• Splits the MS and applies new statistical weights

Usage:

-Create a config, using the example config provided

-python polcal_steps.py <msin> <msout> <msout_target> <output_directory> config.txt

This will output a fully polarimetric calibrated measurement set containing your science target. It is expected to run self-calibration after this.

Software requirements:

CASA
Python3
singularity

Example outputs

Example polynomic functions fitted to the total flux, polarization angle, and linearly polarized fraction against frequency, for the calibrator 3C 138 (used to calibrate the polarization angle).