Title:	Calibration and stokes imaging with full embedded element primary beam model for the Murchison widefield array.
Authors:	Sokolowski, M. Colegate, T. Dwarakanath, K.S. +21 Co-authors
Keywords:	Instrumentation interferometers
Issue Date:	Nov-2017
Publisher:	Cambridge University Press for Astronomical Society of Australia
Citation:	Publications of the Astronomical Society of Australia, 2017, Vol.34, e062
Abstract:	The Murchison Widefield Array (MWA), located in Western Australia, is one of the low-frequency precursors of the international Square Kilometre Array (SKA) project. In addition to pursuing its own ambitious science program, it is also a testbed for wide range of future SKA activities ranging from hardware, software to data analysis. The key science programs for the MWA and SKA require very high dynamic ranges, which challenges calibration and imaging systems. Correct calibration of the instrument and accurate measurements of source flux densities and polarisations require precise characterisation of the telescope's primary beam. Recent results from the MWA GaLactic Extragalactic All-sky MWA (GLEAM) survey show that the previously implemented Average Embedded Element (AEE) model still leaves residual polarisations errors of up to 10-20 % in Stokes Q. We present a new simulation-based Full Embedded Element (FEE) model which is the most rigorous realisation yet of the MWA's primary beam model. It enables efficient calculation of the MWA beam response in arbitrary directions without necessity of spatial interpolation. In the new model, every dipole in the MWA tile (4 x 4 bow-tie dipoles) is simulated separately, taking into account all mutual coupling, ground screen and soil effects, and therefore accounts for the different properties of the individual dipoles within a tile. We have applied the FEE beam model to GLEAM observations at 200 - 231 MHz and used false Stokes parameter leakage as a metric to compare the models. We have determined that the FEE model reduced the magnitude and declination-dependent behaviour of false polarisation in Stokes Q and V while retaining low levels of false polarisation in Stokes U.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/6843
ISSN:	1323-3580 1448-6083(online)
Alternative Location:	http://adsabs.harvard.edu/abs/2017PASA...34...62S http://arxiv.org/abs/1710.07478 http://dx.doi.org/10.1017/pasa.2017.54
Copyright:	2017 Astronomical Society of Australia
Appears in Collections:	Research Papers (A&A)

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