A 189 MHz, 2400 deg2 polarization survey with the murchison widefield array 32-element prototype

G. Bernardi, L.J. Greenhill, D.A. Mitchell, S.M. Ord, B.J. Hazelton, B.M. Gaensler, A. De Oliveira-Costa, M.F. Morales, N.U. Shankar, R. Subrahmanyan, R.B. Wayth, E. Lenc, C.L. Williams, W. Arcus, B.S. Arora, D.G. Barnes, J.D. Bowman, F.H. Briggs, J.D. Bunton, R.J. CappalloB.E. Corey, A. Deshpande, L. Desouza, D. Emrich, R. Goeke, D. Herne, J.N. Hewitt, M. Johnston-Hollitt, D. Kaplan, J.C. Kasper, B.B. Kincaid, R. Koenig, E. Kratzenberg, C.J. Lonsdale, M.J. Lynch, S.R. Mcwhirter, E. Morgan, D. Oberoi, J. Pathikulangara, T. Prabu, R.A. Remillard, A.E.E. Rogers, A. Roshi, J.E. Salah, R.J. Sault, K.S. Srivani, J. Stevens, S.J. Tingay, M. Waterson, R.L. Webster, A.R. Whitney, Andrew Williams, J.S.B. Wyithe

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Abstract

We present a Stokes I, Q and U survey at 189 MHz with the Murchison Widefield Array 32 element prototype covering 2400 deg2. The survey has a 15.6 arcmin angular resolution and achieves a noise level of 15 mJy beam-1. We demonstrate a novel interferometric data analysis that involves calibration of drift scan data, integration through the co-addition of warped snapshot images, and deconvolution of the point-spread function through forward modeling. We present a point source catalog down to a flux limit of 4 Jy. We detect polarization from only one of the sources, PMN J0351-2744, at a level of 1.8% ± 0.4%, whereas the remaining sources have a polarization fraction below 2%. Compared to a reported average value of 7% at 1.4 GHz, the polarization fraction of compact sources significantly decreases at low frequencies. We find a wealth of diffuse polarized emission across a large area of the survey with a maximum peak of 13 K, primarily with positive rotation measure values smaller than +10 rad m-2. The small values observed indicate that the emission is likely to have a local origin (closer than a few hundred parsecs). There is a large sky area at α ≥ 2h30 m where the diffuse polarized emission rms is fainter than 1 K. Within this area of low Galactic polarization we characterize the foreground properties in a cold sky patch at (α, δ) = (4h, -27.°6) in terms of three-dimensional power spectra. © 2013. The American Astronomical Society. All rights reserved.
Original languageEnglish
Pages (from-to)16pp
JournalThe Astrophysical Journal
Volume771
DOIs
Publication statusPublished - 2013

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