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21-11-2012
Tied-Array Beams Combining the Full LOFAR Core - Part I
| Submitter: | Jason Hessels |
| Description: | With the extension of the "Single Clock" distribution to the entire LOFAR Core (see here for more details), it is now possible to form coherent tied-array beams that add the collecting area of up to 24 LBA stations or 48 HBA sub-stations. Previously this was only possible within the 6-station (12 HBA sub-station) Superterp. In these three observations we demonstrate the evolution of LOFAR's sensitivity, starting with the incoherent sum of 40 core HBA sub-stations and progressing to the coherent sum of these. The impact on the off-pulse noise level is obvious and agrees reasonably well with the theoretically expected scaling (note that the center and right observations are not simultaneous and hence there is also some difference due to intrinsic source variability). Furthermore, regular delay calibration observations - analyzed with software developed by Michiel Brentjens - confirms that these delays are stable and known to better than 1 nanosecond. This positive evolution underlines the invaluable improvement that the newly installed Syncoptic Boards have made to the array, as well as the general importance of "intelligent design". In Part II we will present more quantitative examples of the sensitivity improvement as well as tied-array beam maps. We thank the large number of LOFAR developers that have made this possible, and in particular Gijs Schoonderbeek, Klaas Dijkstra, Peter Maat, Klaas Stuurwold and Henry Meulman for their important roles in designing and implementing the Single Clock extension. |
| Copyright: | JWTH/LOFAR |
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