Point source, or not?

[Patrick Slane <slane@head.cfa.harvard.edu>]

Hi folks:

Following our discussion about the aspect solution and the apparent extent to 
the point source in two of the recent observations, I compared this to the 
image from the 50 ks segment taken earlier this year, which was at a different 
roll angle. As others had commented, based upon inspection of earlier 50 ks 
observations, the source does not appear extended.

I've placed a jpg image at 

http://hea-www.harvard.edu/~slane/CasA/ptsrc.jpg

that illustrates the point. The upper images are from ObsIDs 4636 and 4638, 
which are 150 and 170 ks, respectively. These both show a hint of a 
north-south extent (actually a bit northwest-southeast, perhaps). The bottom 
one is from ObsID 5196, the 50 ks observation done earlier in Cycle 5, at 
the same roll angle as the 50 ks observations carried out in earlier cycles. 
Here there is no evidence of extent in this direction. Note that this isn't 
just related to the fact that the exposure is shorter, because the image I 
showed at the meeting was from a 40 ks observation. So, it would appear that 
this is either an aspect or a PSF issue (since the source is off-axis). We'll 
need to investigate that further.

Cheers,

-- Pat