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. Udaya 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, A. 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.

    Original languageEnglish
    Article number105
    JournalAstrophysical Journal
    Volume771
    Issue number2
    DOIs
    Publication statusPublished - 2013

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