[daip] Polarization calibration apply failure.

[R. Craig Walker]

I am processing wideband 43 GHz VLBA data on M87, data taken with the
RDBE's PFB personality.  There are 8 full polarization IFs of 32 MHz
each.  I am attempting a sort-of polarization self-calibration.  I
made images, based on a normal VLBI polarization calibration done with
LPCAL and multi-component models.  There have not been any EVPA
calibration so the images correspond to the R/L phase differences in
the data set.  I ran PCAL using the following parameters to try to
use the I,Q,U (and V - it's there) images as the model:

default pcal
  ind=5; getn 1
  calsour='oj287',' '
  docalib=2; gainuse=19; flagver=4; doband=1; bpver=3
  smooth=6,8,16; ichansel=9,56,1,0
  in2name='OJ287_98A_43';  in2cl='ICL001'; in2s=71; in2d=5; invers=1
  ncomp=0; nmaps=1; cmodel=' '; domodel=1;
  solint=1.0; soltype='rapr'; spectral=1
  inparm=0; prtlev=1; refant=5
  inp pcal
  prtask ' '; clrmsg
go pcal

I've never seen a PD table before, but the one produced looks like I
imagine it
should.  Here is a snippet from PRTAB (the mail tool doesn't like long
lines so it will likely make a mess of this, but you can see the sorts of
values that are being obtained).


Ncol 9  Nrow 10    Sort cols:
    Table has     5 keyword-value pairs:
   NO_ANT   =           10
   NO_POL   =            2
   NO_IF    =            8
   NO_CHAN  =           64
   POLTYPE  =  VLBI
   Table format incompatable with FITS ASCII tables

COL. NO.         1             2            3            4           5    
       6              7              8             9
     ROW      ANTENNA      SUBARRAY      FREQ ID      REFANT      P_DIFF  
   REAL 1         IMAG 1         REAL 2         IMAG 2
  NUMBER
       1          1            1            1            1                
    0.000171      -0.002044       0.059254      -0.023
       1                                                                  
    0.000171      -0.002044       0.059254      -0.023
       1                                                                  
    0.000171      -0.002044       0.059254      -0.023
       1                                                                  
    0.000171      -0.002044       0.059254      -0.023


I then split the data to make new images using:

default split
  ind 5; getn 1
  outcl='SPLIT6'; outd=5; outs=1
  source='3C274',' '
  docalib 2; gainuse 19; doband 1; dopol=1; pdver=1; bpver 3; flagver 4
  bchan 9; echan 56
  douvcomp=-1
  aparm=2, 2.0, 0, 1, 0, 1
go split


The problem is that, after split, the amplitudes and phases are all
identically zero in all 4 stokes (looked at with PRTUV) and presumably
for all time since VPLOT couldn't self scale.  The weights look
normal as does the quantity of data.

If I do: tget split; dopol=0; outcl='split7'; go split, I get a data
set that has normal looking data.  The weights are the same as for
the dopol=1 data set while the amplitudes and phases have the usual
behavior.  So it would seem that something in the application of the
polarization calibration is zeroing the data.

I get the same behavior running VPLOT on the multisource data set and
on source OJ287 (so it's not source dependent).  I am applying
calibration on the fly.   With dopol=0, all is normal.  With dopol=1;
pdver=1, I get a failure to self scale so I presume the data are all
zero.

I presume that this doesn't happen with VLA data, so I must be tickling
some problem unique to my (or the VLBI) case.  Any clue?

The data are on my home machine (MAC) but on a portable drive that could be
brought to work and tried on my laptop (or any with a firewire 800 port).

I don't know if it matters, but the AN table does not have polarization
parameters.  I believe this is normal when working with the PD table.
When I did the LPCAL calibration, it put polarization parameters in the
AN table as usual, but in setting up for PCAL, I deleted that table (after
a TASAV) and copied in the original table.

Cheers

Craig



---------------------------------------------------------------------
    R. Craig Walker            Array Operations Center
    cwalker at nrao.edu           National Radio Astronomy Observatory
    Phone  575 835 7247        P. O. Box O
    Fax    575 835 7027        Socorro NM 87801   USA
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