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A correlator world record (?)

Submitter: John Romein
Description: AARTFAAC (Amsterdam-ASTRON Radio Transients Facility and Analysis Centre) is a project that will use 288 individual LOFAR LBA dipoles on the superterp, to detect transients in the radio sky. With 288 dipoles, no less than 41,328 baselines can be formed, yielding an incredible instantaneous (u, v)-coverage as shown in the left panel. The right panel shows the corresponding array beam pattern with a colorscale in dB. As the Uniboard-based AARTFAAC correlator is not available yet, we abused the LOFAR correlator to create a data set with which the AARTFAAC group can start doing interesting work.

We captured over 3 hours of data from 288 antennas (576 dipoles). Even though we observed only five 195-kHz subbands (59.7 - 60.6 MHz), this already resulted in 27 TB of data. This data was converted as if it originated from 288 real LOFAR stations, to fool the LOFAR correlator. However, the Blue Gene/P cannot handle more than 64 station inputs, so we moved the data to the DAS-4 computer cluster in Dwingeloo (using a 10 Gb/s Ethernet connection), and with a number of quick "hacks", we were able to run the LOFAR correlator on a PC cluster. Using 21 machines, correlating the data took less than 9 hours. At 64 channels per subband, this resulted in 619 billion correlations. We think that correlating 288 dual-polarized antennas broke the world record.

Stay tuned for tomorrow's AJDI, to see the very first AARTFAAC image!

Credits: Stefan Wijnholds (for the pictures) and Menno Norden (for doing impossible things with RSP boards)
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