[GMVAtech 16] Re: Possible Problem in data quality

[Thomas Krichbaum]

Dear colleagues,

we now have checked if bad weather could be the reason for
the poor fringe amplitudes at the VLBA, eg. that it may cause
the huge jumps in amplitudes at KP between 6UT and 7 UT.
The answer is no, the Tsys values are in the typical range
of 100-120 K, so the weather was good. The same is also true
for the poor behaviour of LA between 04-05 UT, again
the Tsys values are normal.

This leads to the conclusion, that it is not the weather which
has led to the poor data quality.

A plot of the Tsys values is attached (for LCP).

kind regards, Thomas + Thalia



On 08/23/2018 12:20 PM, Thomas Krichbaum wrote:
> 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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