A Polarization Calibration Example

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4.4.5.3 A Polarization Calibration Example

In the following example, we do a standard ’D+QU’ solution on the bright source BLLac (2202+422) which has been tracked through a range in parallactic angle:

   default(’polcal’)
   vis                 = ’polcal_20080224.cband.all.ms’
   caltable            = ’polcal.pcal’
   field               = ’2202+422’
   spw                 =         ’’
   solint              =      ’inf’
   combine             =     ’scan’
   preavg              =      300.0
   refant              =     ’VA15’
   minsnr              =          3
   poltype             =     ’D+QU’
   gaintable           = [’polcal.gcal’,’polcal.bcal’,’polcal.xdelcal]
   gainfield           =       [’’]
   polcal()

This assumes setjy and gaincal have already been run. Note that the original gain-calibration table is used in gaintable so that what is in the model is in agreement with what is in the gaintable, rather than using the table resulting from fluxscale.

Now, we need to set the R-L phase using a scan on 3C48 (0137+331):

   default(’polcal’)
   vis                 = ’polcal_20080224.cband.all.ms’
   caltable            = ’polcal.polx’
   field               = ’0137+331’
   refant              =     ’VA15’
   minsnr              =          3
   poltype             =        ’X’
   smodel              = [1.0,-0.0348,-0.0217,0.0]  # the fractional Stokes for 3C48
   gaintable           = [’polcal.gcal’,’polcal.bcal’,’polcal.xdelcal’,’polcal.pcal’]
   polcal()

Note that the fractional polarization of 3C48 has been properly specified in smodel here.

If, on the other hand, we had a scan on an unpolarized bright source, for example 3C84 (0319+415), we could use this to calibrate the leakages:

   default(’polcal’)
   vis                 = ’polcal_20080224.cband.all.ms’
   caltable            = ’polcal.pcal’
   field               = ’0319+415’
   refant              =     ’VA15’
   poltype             =     ’D’
   gaintable           = [’polcal.gcal’,’polcal.bcal’,’polcal.xdelcal]
   polcal()

We would then do the ’X’ calibration as before (but using this D-table in gaintable).

A full processing example for continuum polarimetry can be found in § F.2.

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