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Abstract: AIMS: To demonstrate and test the capability of the next generation oflow-frequency radio telescopes to perform high resolution observations acrossintra-continental baselines. Jupiter-s strong burst emission is used to performbroadband full signal cross-correlations on time intervals of up to hundreds ofmilliseconds. METHODS: Broadband VLBI observations at about 20 MHz on abaseline of ~50000 wavelengths were performed to achieve arcsecond angularresolution. LOFAR-s Initial Test Station LOFAR-ITS, The Netherlands and theNancay Decametric Array NDA, France digitize the measured electric field with12 bit and 14 bit in a 40 MHz baseband. The fine structure in Jupiter-s signalwas used for data synchronization prior to correlation on the time-series data.RESULTS: Strong emission from Jupiter was detected during snapshots of a fewseconds and detailed features down to microsecond time-scales were identifiedin dynamic spectra. Correlations of Jupiter-s burst emission returned strongfringes on 1 ms time-scales over channels as narrow as a hundred kilohertzbandwidth. CONCLUSIONS: Long baseline interferometry is confirmed at lowfrequencies, in spite of phase shifts introduced by variations in ionosphericpropagation characteristics. Phase coherence was preserved over tens tohundreds of milliseconds with a baseline of ~700 km. No significant variationwith time was found in the correlations and an estimate for the fringevisibility of 1, suggested that the source was not resolved. The upper limit onthe source region size of Jupiter Io-B S-bursts corresponds to an angularresolution of ~3 arcsec. Adding remote stations to the LOFAR network atbaselines up to thousand kilometers will provide 10 times higher resolutiondown to an arcsecond.

Autor: A. Nigl, P. Zarka, J. Kuijpers, H. Falcke, L. Baehren, L. Denis

Fuente: https://arxiv.org/

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