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Stefan J. Wijnholds, Jaap D. Bregman, Albert-Jan Boonstra, "Sky Noise Limited Snapshot Imaging in the Presence of RFI with LOFAR's Initial Test Station", Experimental Astronomy, V17, pp35-42, 2004 abstract: The Initial Test Station is the first full scale prototype of a LOFAR station. It operates in the 10-40MHz range and consists of 60 sky noise limited dipoles arranged in a five-armed spiral structure offering an instantaneous synthesized aperture of almost 200m diameter. We will present all sky snapshot images demonstrating sky noise limited imaging capability in the presence of a strong RFI source that exceeds the sky noise dominated system temperature by 27 dB. This result is obtained with a two stage self-calibration procedure. First the RFI source is used as calibrator and then subtracted, after which Cas A shows up at a level that is a factor 2000 lower and then dominates the picture with its side lobes. A second self calibration on Cas A, which has a different position, then reveals the same extended galactic emission as found in a RFI free adjacent spectral channel. This demonstrates that a single 10 kHz channel of a 6.7 s snapshot of a single LOFAR station already provides a dynamic range of over 104. |