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Twinkle, twinkle little star

Submitter: Stefan Wijnholds
Description: This movie gives an overview of the achievements of the ionospheric scintillation station calibration process by showing its results over 300 consecutive 1 s snapshots at 50 MHz. For each RFI free snapshot a calibrated all-sky image (top left), a calibrated all-sky map of extended emission (top right), the difference between the two maps showing only point source emission (bottom left) and a plot of the source flux of Cyg A and the reference source Cas A versus time (bottom right) is shown. The blue line in the bottom right plot indicates which snapshot is shown in the maps.

Since Cas A is used as flux reference, the green dots should be interpreted as the Cyg A-Cas A-flux ratio, showing that this ratio can change by a factor 4 within seconds! These variations may be explained by ionospheric turbulence causing focusing and defocusing of emission from celestial sources on the ground. The question whether Cas A and Cyg A are equally affected can not be answered by these plots, and is still subject of debate.

These results were obtained from data captured on CS10 starting at 2:18:47 UTC on February 15, 2008 by estimating the complex gain per element, the contribution of extended emission on short baselines and the power of Cas A and Cyg A for a total of 860 free parameters solved in only 0.4 s on a single core of a 2.0 GHz CPU.
Copyright: Stefan Wijnholds
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