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

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

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...

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Bibliographic Details
Main Authors: Bernardi, G ., Greenhill, L., Mitchell, D., Ord, S., Hazelton, B., Gaensler, B., de Oliveira-Costa, A., Morales, M., Udaya Shankar, N., Subrahmanyan, R., Wayth, Randall, Lenc, E., Williams, C., Arcus, Wayne, Arora, B., Barnes, D., Bowman, J., Briggs, F., Bunton, J., Cappallo, R., Corey, B., Deshpande, A., deSouza, L., Emrich, David, Goeke, R., Herne, D., Hewitt, J., Johnston-Hollitt, M., Kaplan, D., Kasper, J., Kincaid, B., Koenig, R., Kratzenberg, E., Lonsdale, C., Lynch, Mervyn, McWhirter, S., Morgan, E., Oberoi, D., Pathikulangara, J., Prabu, T., Remillard, R., Rogers, A., Roshi, A., Salah, J., Sault, R., Srivani, K., Tingay, Steven, Waterson, Mark, Webster, R., Whitney, A., Williams, A., Wyithe, J.
Format: Journal Article
Published: Institute of Physics Publishing, Inc. 2013
Subjects:
radio continuum: general
polarization
ISM: magnetic fields
surveys
diffuse radiation
techniques: interferometric
Online Access:http://hdl.handle.net/20.500.11937/32095
Description
Summary: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 >= 2h30m 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.

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