[evlatests] A Most Bizarre Event

[Dan Mertely]

Hi Rick.  I just checked the W8monitor plot for yesterday, around
6:30 PM and didn't see anything out of the ordinary.  It seems
unlikely that ea05 RCP saw it, otherwise it should have shown up on
the plot. (attached)  -Mert


Rick Perley wrote:
>     The short L-band observation taken last night (around 7PM) was 
> affected by an event of unknown origin which greatly modified the 
> switched power table for one scan. 
> 
>     There are four scans, two of the calibrator and two of a nearby 
> (offset 1 degree or so) blank field. 
> 
>     The first three scans are completely normal.  All switched power and 
> visibility values appear normal. 
>     The last scan (duration ~ 2 minutes) was disrupted by some sort of 
> event which greatly modified all switched power values, and the 
> visibilities. 
> 
>     The major characteristics are:
> 
>     1) All antenna were affected equally. 
>     2) All subbands were affected, but not in the same way. 
>     3) Effects were seen in both PDif and PSum, but they are not the same. 
>     4) The effect caused the monitored power to change *smoothly* during 
> the 2 minute scan.  The preceding scan (a few seconds earlier and only 1 
> degree away) is fine. 
>     5) The effect is *much* stronger in RCP.  For some subbands, there 
> is no effect at all in LCP. 
> 
>     Most remarkable is how the PDif and PSum were affected differently, 
> for different subbands.   In all cases, the PDif dropped, typically by a 
> factor of four.  For one subband (4), PDif is actually negative!  But 
> PSum dropped for 12 subbands, and rose for the other four.  The four 
> subbands with an apparent power increase are:  4, 9, 10, and 15.  All 
> antennas apparently behave in the same way. 
>     It's hard to imagine how the switched power can drop by a factor of 
> 4 while the summed power can rise by about the same factor. 
> 
>     I've looked at the cross-power spectra, and there is certainly 
> strong evidence of an unusual event, seen in some subbands, occuring 
> during this time.  Some spectra are simply blank (presumably, all 
> integer zero), and others are clearly messed up.  But other subbands 
> look fine during this time -- but evidently are not, as judged by the 
> system power monitors. 
> 
>     The IAT time for this event was from 1:38 through 1:42 (or, 6:38 to 
> 6:42, PM, local time).  It would be useful for someone to look at other 
> monitors to see if something very odd was occurring then.
> 
> 
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