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31st of May 2021
ASKAP update for May
by Aidan Hotan
The ASKAP Update for May reports on factors impacting the time scale of Pilot Surveys Phase II, the latest improvements to ASKAPsoft, continuum image quality and CASDA commensality. Feedback from Pilot Survey Phase I WALLABY data showed that the standard processing parameters were leaving significant residual structure in continuum images, especially around extended sources. Comparison with other tools and exploration of parameter space shows that with correct flagging, the main factor is the number of self-calibration and cleaning stages allowed.

The image above shows the evolution of image quality with successive cycles of self-calibration and cleaning around an extended source (with a uniform colour scale). The upper left panel has only bandpass calibration applied, the next two panels apply phase-only self-calibration and the final 5 show successive iterations with amplitude and phase self-calibration. The current processing strategy stops at the second panel, but at least another two iterations may be justified despite the computational penalty. While it is possible to improve the image quality with more cycles, this will come at the expense of processing time, which may impact ASKAP’s observing efficiency. Efforts to find the best compromise strategy will continue with Phase II quality gates. (Image credit: Mark Wieringa)

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