[daip] Re: SDA in VLA datasets

[douglas bock]

> 	Is the form of the artefact stable?  in other words, when imaging
> the days separately, does it look the same?  Forgetting about hardware
> problems for a moment, have you considered the following possible causes
> for the artefact:

Walter,

Thanks for your suggestions.

I should have included you on the initial summary email that I sent to the
others (it follows in a moment).

>
> 1.	Phase errors -- your observations were made at very low
> elevations.  I suspect that the isoplanatic patch size is smaller than
> your field of view, so even self cal might not fix the problem.
> Test : image different days / time ranges, and look for variation.
>

(see the other email)

hmm. we self-calibrated on the pulsar ("on" part of the period) and then
copied the solution to the "off" data. Averaged over the period, the
pulsar dominates all other emission in the field, and was either at the
phase center or 1 arcmin away. Meanwhile, we image a resolved galaxy 3 (or
2) arcmin north of the phase center pretty well (it has been uv-subtracted
from the images on my website, and is outside the box of the gif plots).

> 2.	Could there be very large extended emission nearby that is barely
> detected by the interferometer?  Test : image long and short baselines
> separately and see if it cleans up in the long baseline image.

I have filtered out some very extended emission (arcmin scale) by ignoring
the relevant uv data, to the point where I can't see it in any image. I'll
try with a more severe filtering.

>
> 3.	Are your antennas shadowing at all?  (fillm will alert you about
> this)

There was no shadowing, according to a quick check with miriad (I did not
run FILLM; Richard did and is traveling).

>
> 4.	Were the antennas recently reconfigured?  Ken Sowinski might
> know if the baselines put into the data at that time were good or not.
>

array was recently reconfigured, since it was BnA, and the VLA is not in
that for long. There was a note to this effect in the log file.