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Register a new userA 189 MHz, 2400 square degree polarization survey with the Murchison Widefield Array 32-element prototype
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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 square degrees. The survey has a 15.6 arcmin angular resolution and achieves a noise level of 15 mJy/beam. 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 catalogue 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 pm 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 2^h30^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 $(alpha,delta) = (4^h,-27^circ.6)$ in terms of three dimensional power spectra
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We present new wide-field observations of Centaurus A (Cen A) and the surrounding region at 118 MHz with the Murchison Widefield Array (MWA) 32-tile prototype, with which we investigate the spectral-index distribution of Cen As giant radio lobes. We compare our images to 1.4 GHz maps of Cen A and compute spectral indices using temperature-temperature plots and spectral tomography. We find that the morphologies at 118 MHz and 1.4 GHz match very closely apart from an extra peak in the southern lobe at 118 MHz, which provides tentative evidence for the existence of a southern counterpart to the northern middle lobe of Cen A. Our spatially-averaged spectral indices for both the northern and southern lobes are consistent with previous analyses, however we find significant spatial variation of the spectra across the extent of each lobe. Both the spectral-index distribution and the morphology at low radio frequencies support a scenario of multiple outbursts of activity from the central engine. Our results are consistent with inverse-Compton modelling of radio and gamma-ray data that supports a value for the lobe age of between 10 and 80 Myr.
The Murchison Wide-field Array (MWA) is a low frequency radio telescope, currently under construction, intended to search for the spectral signature of the epoch of re-ionisation (EOR) and to probe the structure of the solar corona. Sited in Western Australia, the full MWA will comprise 8192 dipoles grouped into 512 tiles, and be capable of imaging the sky south of 40 degree declination, from 80 MHz to 300 MHz with an instantaneous field of view that is tens of degrees wide and a resolution of a few arcminutes. A 32-station prototype of the MWA has been recently commissioned and a set of observations taken that exercise the whole acquisition and processing pipeline. We present Stokes I, Q, and U images from two ~4 hour integrations of a field 20 degrees wide centered on Pictoris A. These images demonstrate the capacity and stability of a real-time calibration and imaging technique employing the weighted addition of warped snapshots to counter extreme wide field imaging distortions.
It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky.
Significant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the Southern Hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21 cm emission from the epoch of reionisation in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophysics; and solar, heliospheric, and ionospheric science and space weather. The Murchison Widefield Array is located in Western Australia at the site of the planned Square Kilometre Array (SKA) low-band telescope and is the only low-frequency SKA precursor facility. In this paper, we review the performance properties of the Murchison Widefield Array and describe its primary scientific objectives.
The Murchison Widefield Array (MWA) is one of three Square Kilometre Array Precursor telescopes and is located at the Murchison Radio-astronomy Observatory in the Murchison Shire of the mid-west of Western Australia, a location chosen for its extremely low levels of radio frequency interference. The MWA operates at low radio frequencies, 80-300 MHz, with a processed bandwidth of 30.72 MHz for both linear polarisations, and consists of 128 aperture arrays (known as tiles) distributed over a ~3 km diameter area. Novel hybrid hardware/software correlation and a real-time imaging and calibration systems comprise the MWA signal processing backend. In this paper the as-built MWA is described both at a system and sub-system level, the expected performance of the array is presented, and the science goals of the instrument are summarised.
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