Calibrating using two different phase calibrators

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Calibrating using two different phase calibrators

Postby JCollier » Thu Apr 07, 2016 4:50 pm

We have a set of 4cm CABB observations covering many sources across the southern sky. The observer scheduled the observations such that each source has its own nearby phase calibrator, which is visited only once per cycle, before the source, and which is followed by a scan of another calibrator, nearby the next source. We're interested in only one source, which happens to be followed by 1934-638. Therefore, we can use 1934-638 for flux density and bandpass calibration.

As for phase calibration, we'd ideally interpolate between the bracketing scans using the two phase calibrators. Is this possible? Alternatively, we could possibly extrapolate from all ~2 mins of the scan of the phase calibrator before hand, although the sources are typically observed for ~8 mins, so the phases may significantly change. Presumably you could do this with gpaver.
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Re: Calibrating using two different phase calibrators

Postby ste616 » Fri Apr 08, 2016 9:58 am

Hi Jordan,

As for phase calibration, we'd ideally interpolate between the bracketing scans using the two phase calibrators. Is this possible?


Technically, it is easy to do with gpcopy (mode=merge). But realistically, it isn't going to help. There is no reason to expect that the phase on a calibrator in one part of the sky is going to be related to the phase on a calibrator in a different part of the sky, unless the atmosphere is very stable.

Alternatively, we could possibly extrapolate from all ~2 mins of the scan of the phase calibrator before hand, although the sources are typically observed for ~8 mins, so the phases may significantly change. Presumably you could do this with gpaver.


I think this is your only option. Yes, the phase may significantly vary, but if that is the case, then trying to interpolate between scans on different sources is not going to help you anyway. I don't think you need to use gpaver though - I think Miriad will by default just try to get the last calibration value it can and apply it. I could be wrong though...
cheers
Jamie Stevens
ATCA Senior System Scientist
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