Polarisation Calibration

The purpose of polarisation calibration is to calibrate the voltage data against a known polarisation source, such as the VELA pulsar and make sure the polarisation products we receive are correct. There are two stages to this, polcal and apply_polcal.

POLCAL

polcal.py -options

Main script used to derive proper polarisation calibration solutions by testing current FRB X and Y products against models of known pulsars, i.e. VELA and 1644.

Parameters

params.centre_freq_polcal - Central frequency of polarisation calibrator observing band, usually same as FRB.

params.polcal_pa0 - Polarisation Position Angle (PA) at known reference frequency f0.

params.polcal_f0 - Reference frequency of PA angle.

params.polcal_l_model - Known model of stokes L/I as a function of frequency for pol calibrator.

params.polcal_v_model - Known model of stokes V/I as a function of frequency for pol calibrator.

params.polcal_priors - Yaml file of priors used for polcal.

params.polcal_peak_w = 0 - Width in samples of boxcar taken across average pulse profile of pol calibrator centered at peak.

params.polcal_rms_w = 40 - Width in samples of boxcar taken off-pulse to estimate RMS noise.

params.polcal_tN = 100 - Number of samples to average over.

params.polcal_fN = 1 - Number of channels to average over.

params.polcal_guard = 0.1 - Width in phase units (from [0 - 1]) between on-pulse boxcar and off-pulse boxcar.

params.polcal_chanflag = "" - String of flagged channels (in MHz). E.g "800,850" or can specify a range "800:900" or a combination of both.

params.polcal_cpus = 1 - Number of cpus i.e. walkers for polcal fitting.

params.polcal_live = 1000 - Number of live steps in fitting.

params.polcal_ellipse = False - Toggle ellipticity angle fitting (elliptical polarisation).

APPLY POLCAL

apply_polcal.py -options

Script to apply polcal solutions to the High time resolution X and Y products of FRB.

params.polcal_fast = True - Toggle if you want to make this process go fast. Depreciated given recent updates to beamforming pipeline.