[evlatests] Something to worry about?

[Bob Sault]

Rick,

It could be a Gibbs ghost or some other edge effect in the bandpass.
Does is change if you liberally discard channels at the ends of the
band?

Best regards
Bob

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Phone:    +61-2-98721028
Email:    rsault at nrao.edu
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-----Original Message-----
From: evlatests-bounces at nrao.edu [mailto:evlatests-bounces at nrao.edu] On
Behalf Of Rick Perley
Sent: Saturday, 3 December 2011 10:37 AM
To: evlatests at aoc.nrao.edu
Subject: [evlatests] Something to worry about?

      I attach something which I hope is a curiosity, but may portend 
something more worrisome ...     

    The northern-stability test was done on the source known as 
J0019+7327.  Unbeknown to me, this object has a quite strong nearby 
neighbor.  At 1441 MHz, the neighbor is about 1/4 the brightness of the 
target source, and is located 20 arcminutes to the SE.  After correction 
of the primary beam, its peak brightness is about 620 mJy/beam, while 
the target source is 550 mJy/beam. 

    The image is quite nice, but look at the position diametrically 
opposite the bright neighbor -- there is a clear 'anti-source', which is 
*exactly* located on the reflected position of the bright neighbor.  The 
usual self-calibration (where the anti-source is excluded from the 
model) is unsuccessful in removing the 'hole'.   The hole depth is only 
a few mJy, so the effect is small.  But is it real?  And if so, what did it?

    I attach a .png file for viewing.