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E-LOFAR calibration challenges - the cruel sea ?

Submitter: Michael Garrett
Description: The expansion of LOFAR across Europe (E-LOFAR) is an exciting new development that in principle will permit images of the low-frequency radio sky to be made with sub-arcsecond angular resolution. The challenges and problems of calibrating E-LOFAR are highly topical, leading to much abstract discussion.

Real observations, such as the recent low frequency (327 MHz) VLBI observations - see Lenc et al.2007, ApJ http://xxx.lanl.gov/pdf/0710.1946 - suggest that the E-LOFAR calibration problem is tractable (see also AJPoD 21-08-2007), certainly for a large fraction of the sky observed by the LOFAR High Band Antennas (HBAs). In addition, to surveying the properties and nature of potential E-LOFAR calibrators (and targets), Lenc's VLBI observations can also provide useful information on the likely spatial and temporal stability of the ionosphere. The movie presented above was created by Emil Lenc (JIVE summer-student 2006, PhD student Swinburne). It shows the phase corrections determined for over a dozen sources separated by a few degrees on the sky. Using wide-field VLBI techniques, these sources are simultaneously detected within the main beam of each individual antenna and their phases can be solved for simultaneously. The movie gives a qualitative idea of the stability of the ionosphere as the phase corrections appear to move like a rolling sea across each of the antenna sites.

(See also Lenc, E., Garrett, M.A., Wucknitz, O., Anderson, J., Tingay, S., 2008. Astrophysical Journal, 673, 78.)
Copyright: Centre for Astronomy & Supercomputing, Univ. Swinburne
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