[daip] RE: Pband issues

[Namir E. Kassim]

> Problem 2.5  Total field was reconstructed using FLATN.

did you get all the statistics discussed in your note from FLATN images? i
recall there was something wrong with FLATN for flux densities - you should
use it to make pretty images but not to make flux measurements (which should
be done from individual facet maps). or at least it used to be like that,
and maybe now it's fixed, i forget. the error is not so bad, i forget the
level, so it may or may not be connected with your problems.

another comment is that one of the things that will stop you from reaching
thermal noise at P band (in addition to confusion) is that the primary beam
is asymetric (and of limited accuracy even if it was symetric, Rick can
probably quantify). but of course the PB correction does not know about this
(time variable) assymetry. so obviously this leads to problems, and may (or
actually must) account for why the same sources measured in different parts
of overlapping fields give (slightly) different answers. but i'm not sure if
the level of this error can account for the problems you're seeing. i
suppose this problem is alleviated the longer the integration (and hence PB
rotation on the sky) per field, so the effect kind of smears out. if you did
all snapshots maybe the problem is compounded.

how much SELFCALing was done? just phase, or amplitude and phase? one of the
problems with the asymetric primary beam is that  strong sources appear to
go up and down in flux as the PB rotates on the sky - A&P selfcal then tries
to compensate by adjusting the gains - all very messy - but again the
question is whether these known errors are at the level you are concerned
about.

last comment - D array P band is always messy, it may be some artifact of
general confusion that is causing your problems, i'm not sure. the images
aaron and i have been working with lately for extragalactic sources are
rarely D array, so you may be running into problems we usually don't face. i
presume you allowed SETFC to find all the nearby confusing sources outside
the main field of view, for example if Virgo or some other strong source is
even 10-20 degrees away you can get strange effects. check 3C catalog to be
sure, make sure there are no biggies out there. where are you pointed?

still digesting ...

-Namir