[evlatests] X-band source displacements

[Ed Fomalont]

Radio positions from the X1925 data, taken on October 13

8 IFs' covering nearly 1 GHz

Frequency range 8.864 to 7.968 GHz


RESULTS at X-band:

1. The source positions are displaced in a direction away from the
phase reference source.

2. The angular displacement is about 0.5 times that seen at C-band.

3. The phases again show no slope across the x-band frequency band.


More details:

Source 1925+211 was used as the main phase reference calibrator

The positions for the other three sources were AGAIN RADIALLY OUTWARD
displaced from their expected position.

(1) (2) (3) (2)/(3) (3)/(2)
SOURCE DISTANCE FROM 1925 OFFSET POSITION
SEP PA SEP PA
(deg) (deg) (asec) (deg)
1931+227 1.80 44.2 0.23 30.0 28170 0.000036
1922+155 5.99 187.8 0.66 194.1 32670 0.000031
1902+319 11.75 -26.0 1.51 -22.0 28013 0.000036
AVG 29000 0.000034 (2)

at Cband we obtained an angular stretching of 12820 0.000078 (3)

Thus, the Cband/Xband ANGULAR stretching is about 2.3 +/- 0.2 times larger

This is close to, but not exactly, the frequency ratio between
(X-band / C-band) = 1.8

C-band 4.8 GHz * 0.000078 = 374 KHz possible freq. offset
X-band 8.4 GHz * 0.000034 = 285 KHz possible freq. offset

It is unclear the 'proper' frequency one should use for C and X-band
to convert the stretching into an effective frequency offset.


ALSO
the phases all constant across the entire frequency band at any one 
time/baseline,
regardless of the average phase offset.