[daip] forwarded message from papadop at phys.ethz.ch

[Eric Greisen]

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From: papadop at phys.ethz.ch
To: Eric Greisen <egreisen at nrao.edu>
Subject: A question regarding flux-calib after flagging
Date: Sun, 12 Dec 2004 19:07:47 +0100

Hi Eric, here I am again, that 300 sigma observer....Padelis Papadopoulos.


I think now I have a good feel of how flux calib works, namely, the GCAL
in the CALIB program, goes ahead (when I run it for both primary and
secondary) and solves the gains for the primary calibratory, per antenna
as it does for the 2ndary.  Then GETJY  goes ahead and scale the SNs
of the 2ndary using the gain solutions found for the primary (I guess it 
will
be a scaling of the amplitudes  only?), the latter having the correct 
*absolute*
values since we know the flux of the primary.

1) If one is forced to flag an antenna only for the primary (I had to do 
that a few
    times) but not the secondary,  then naturally no gain solution and 
flux-scaling factor will
    be present for that antenna for the primary, so what scaling factor 
is then used for
    that antenna to scale the SNs of the 2ndary in the GETJY procedure
    (an average of all other ones, a standard 0-th order value)???


2) After GETJY I get consistent flux values for my secondary, between 
the 2 IFs
    as well as for the two freq IDs (they are all very close in 
frequency), in several
    consecutive days. That value is 3.55 Jy (with a variation of at most 
0.05 Jy among
     days and freq IDs). In *one* day though I get
     S=3.21+/-0.05 Jy for both IFs, and Freq ID=1
     S=3.55+/-0.05 Jy for both IFs and Freq ID=2.
     Unlike other cases the disagreement stays no matter what plausible 
flagging I do
     (on other occasions, flagging a bad antenna or two always brought 
the estimates
      of S between the two freq IDs into agreement in all days).
     any suggestion on this?


many thanks for your help on this,

Cheers

The "pest" Papadopoulos



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