A 189 MHz, 2400 deg²POLARIZATION SURVEY WITH THE MURCHISON WIDEFIELD ARRAY 32-ELEMENT PROTOTYPE

Abstract

We present a Stokes <i>I</i>, <i>Q</i> and <i>U</i> survey at 189MHz with the Murchison Widefield Array 32 element prototype covering 2400deg<sup>2</sup>. The survey has a 15.6arcmin angular resolution and achieves a noise level of 15mJybeam<sup>1</sup>. 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 4Jy. 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 1.4GHz, 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 +10radm<sup>2</sup>. 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 ≥ 2<sup>h</sup>30<sup>m</sup> where the diffuse polarized emission rms is fainter than 1K. Within this area of low Galactic polarization we characterize the foreground properties in a cold sky patch at (α, δ) = (4<sup>h</sup>, 27<img src="http://ej.iop.org/icons/Entities/fdg.gif" alt="fdg" align="bottom">6) in terms of three-dimensional power spectra