Novel technique for wide-field polarimetry with a radio telescope array

Abstract

We report the use of the Australia Telescope Compact Array (ATCA) to conduct polarimetric observations of the sky at 5 GHz. The ATCA is normally operated as an interferometer array, but these observations were conducted in a split-array mode in which the antenna elements were used as single dishes with their beams staggered to simultaneously cover a wide area of sky with a resolution of 10'. The linearly polarized sky radiation was fully characterized from measurements, made over a range of parallactic angles, of the cross-correlated signals from the orthogonal linear feeds. We describe the technique and present a polarimetric image of the Vela supernova remnant made as a test of the method. The development of the technique was motivated by the need for wide-field imaging of the foreground contamination of the polarized component of the cosmic microwave background signal.