[evlatests] Some Good WIDAR news

[Rick Perley]

    Imaging of the fourth L-band sub-band (1684 -- 1812 MHz) has given 
some impressive results. 

    This sub-band is nearly completely free of RFI, so I separated it 
out as a separate database.   Editing and calibrating it went by 
standard methods.  A single (5-hour long) BP was done. 
    The data were split out into a database with 10 channels, each of 10 
MHz width, to reduce chromatic aberrations.  The bandpass program BPASS 
was used to generated time-frequency solutions, every 15 seconds.   
Discrepant data were flagged (nearly all in the first 10 Mhz subband, 
which had some light RFI). 

    The full 100 MHz image has an impressive peak/noise of 218,000:1, 
using a far corner to estimate the noise.  The 'noise' near the 13,000 
mJy point source is a few times larger, and is clearly due to slowly 
changing errors which are not being calibrated out.  I have not 
attempted a closure calibration  yet. 
    A single 10 MHz BW image was made -- the error patterns are the same 
(indeed, each of the 10 channels shows the same error pattern).  The 
far-out noise is larger by a factor of 2.5, rather than 3 as expected -- 
meaning the noise is not decreasing as sqrt(B).  I checked the noise in 
each of the 10 individual pseudo-continuum images -- except for the 
first (RFI), the center 7 'channels' have the same noise (0.16 mJy).  
Channels 2 and 10 are 0.19.  Channel 1 is 0.26 (presumably due to 
left-over RFI). 

    Bottom Line:  The images are very good.  There is no sign of serious 
errors.