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RFI at high time resolution

Submitter: Paolo Serra and the Apertif team
Description: Radio-Frequency Interference (RFI) represents a major challenge for astronomers working with radio data. For example, RFI between 1 and 1.4 GHz will affect the outcome of future surveys such as those planned with Apertif, in particular in unprotected bands.

In this image we show that at least some RFI could be eliminated by processing the data at high time resolution before correlation. The top panel shows an RFI line at ~1.149 GHz on a frequency-vs-time plane as seen by a WSRT antenna. The data are shown at a 10-second time resolution. At this resolution 100% of the data should be thrown away. However, zooming in along the time axis (second panel) shows that the RFI source is not on all the time. For example, using the red line as a separation between good and RFI-polluted data only ~20% of the data are flagged (third panel). Once this is done the data can be averaged to a lower time resolution. The last panel shows that this procedure essentially removes the RFI, but ~80% of the data are still available!

Implementation of this technique for future surveys will be important to collect useful data in frequency ranges severely affected by RFI of this kind.
Copyright: Apertif team
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