[evlatests] Something to worry about?
Rick Perley
rperley at nrao.edu
Fri Dec 2 18:37:09 EST 2011
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.
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