[evlatests] Calibrator Polarizations from 1 to 50 GHz

[Rick Perley]

    The 'flux densities' run has given us the calibrator source 
polarizations, spanning the entire range between 1 and 50 GHz.  I give 
below, at selected frequencies, the *fractional* polarizations, in 
percent, and the *true position angle* for the four primary 
calibrators.  All position angles are referenced to 3C286 = 33 degrees. 

Freq.           3C48             3C138              3C147           3C286
---------------------------------------------------------------------------------
1050            .35  25          5.58   -14         <.05   xxx          8.6
1450           .50  140         7.50   -11         <.05   xxx          9.45
1640           .65  -5           8.45   -10         <.04   xxx           
9.86
1950           .86  +30        9.00   -10         <.04   xxxx       10.12
2450          1.40  60        10.45   -9          <.05    xxx        10.50
2950          2.00 80          10.75  -10          <.05   xxx       10.75
3250          2.50  88         10.02  -10        <.04    xxx        10.90
3750          3.20  96          RFI                <.04     xxx        11.10
4500          3.85  105       10.0    -11         .12    -100        11.25
5000          4.20  108       10.4   -11         .32        0          11.40
6500          5.20  112       9.80  -12          .25     -65          11.62
7250          5.25  113       10.0  -12          .57     -39          11.70
8100          5.35  -65        10.4   -11         .70   -25            11.95
8800          5.40  -63        10.1    -9          .77   -12            11.9
12800        6.00  -63        8.4      -8          2.2    42            11.9
13700        6.10   -63       7.9   -8             2.4    47            11.9
14600        6.40   -64       7.7   -9             2.7    52            12.1
15500        6.45   -65       7.4   -10           2.9    58            12.2
18100        6.90   -68       6.7   -14           3.4     65           12.5
19000        7.1     -69       6.5   -15           3.5     66           12.5
22400        7.7     -72       6.7   -18           3.8   73             12.6
23300        7.8     -72       6.6   -19           3.8   74             12.6
36500        7.4     -80      6.6    -27           4.4   82             13.1
43500        7.5    -88       6.5   -30            5.2   83             13.2
---------------------------------------------------------------------------------

    The interesting new behavior is that of 3C138 -- the fractional 
polarizations at high frequencies have dropped considerably, and the 
p.a. has changed over the past 10 years:  In 2000, the fractional 
polarization was uniformly 11.5% from 4.5 through 45 GHz, and the 
position angle slowly changed from -11 degrees at 5 GHz to -16 at 45 
GHz.  This source has doubled its high frequency flux density over this 
period of time, so we are clearly seeing the effects of a new 'blob' 
with a different polarization p.a.