[GMVAtech 15] Possible Problem in data quality

[Thomas Krichbaum]

Dear colleagues,

we have taken a closer look at the 3C279 data, which where observe with
the GMVA on April, 1 2017 (day 91, exp MM007B (Marscher) = c171c.

http://www.vlba.nrao.edu/astro/VOBS/astronomy/mar17/c171c/

The data were fringe fitted in AIPS in the standard way, with a manual
phasecal to aligne IFs and a global fringe fit combining all IFs
(aparm5=1). The exported to difmap via SPLIT.

The attached plots show the visibility amplitudes coherently time
averaged to 6 secs in uncalibrated correlator units. The *ps files shows
all data, the files 3C279-BR_1.png and 3C279-LA_1.png a smaller subset
on a larger plotting scale.

Mainly for the VLBA we see large scan to scan variations with amplitudes
changing by a factor of up to 3.

Zooming into individual scans show quasi-periodic oscillations within
a scan on time scale of 3-5 minutes (3C279-LA_zoom.png).

Though some of this might be related to bad weather at some VLBA sites,
I am a bit puzzled if there are additional effects. It will take some
time to check other experiments.

best Thomas + Thalia



-- 
Dr. Thomas P. Krichbaum
Max-Planck-Institut fuer Radioastronomie
Auf dem Huegel 69
D-53121 Bonn / Germany

Mail: tkrichbaum at mpifr-bonn.mpg.de
Tel.: (Germany +49)-228-525-295
Web : http://www.mpifr-bonn.mpg.de/research/vlbi
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