A 189 MHz, 2400 deg2 polarization survey with the Murchison Widefield Array 32-element prototype

Gianni Bernardi, Lincoln Greenhill, Daniel A Mitchell, Stephen M Ord, Bryna J Hazelton, Bryan Malcolm Gaensler, Angelica de Oliveira-Costa, Miguel F Morales, Natarajan Udaya-Shankar, Ravi Subrahmanyan, Randall B Wayth, Emil Lenc, Christopher L Williams, Wayne Arcus, Balwinder Singh Arora, David Graeme Barnes, Judd D Bowman, Frank Briggs, John Bunton, Roger CappalloBrian E Corey, Avinash Deshpande, Ludovico deSouza, David Emrich, Robert F Goeke, David Edwin Herne, Jacqueline N Hewitt, Melanie Johnston-Hollitt, David L Kaplan, Justin C Kasper, Barton B Kincaid, Ronald Koenig, Eric Kratzenberg, Colin J Lonsdale, Mervyn John Lynch, Stephen Russell McWhirter, Edward H Morgan, Divya Oberoi, Joseph Pathikulangara, Thiagaraj Prabu, Ronald A Remillard, Alan E E Rogers, Anish A Roshi, Joseph E Salah, Robert John Sault, K S Srivani, Jason A Stevens, Steven John Tingay, Mark F Waterson, Rachel Lindsey Webster, Alan R Whitney, Andrew J Williams, J Stuart B Wyithe

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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 a = 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 (a, d) = (4h, -27.?6) in terms of three-dimensional power spectra.
Original languageEnglish
Pages (from-to)1 - 16
Number of pages16
JournalThe Astrophysical Journal
Issue number2 (Art # 105)
Publication statusPublished - 2013
Externally publishedYes

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