This paper describes the system architecture of a newly constructed radio telescope - the Boolardy Engineering Test Array, which is a prototype of the Australian Square Kilometre Array Pathfinder telescope. Phased array feed technology is used to for
m multiple simultaneous beams per antenna, providing astronomers with unprecedented survey speed. The test array described here is a 6-antenna interferometer, fitted with prototype signal processing hardware capable of forming at least 9 dual-polarisation beams simultaneously, allowing several square degrees to be imaged in a single pointed observation. The main purpose of the test array is to develop beamforming and wide-field calibration methods for use with the full telescope, but it will also be capable of limited early science demonstrations.
We present spectropolarimetric radio images of the supernova remnant (SNR) G296.5+10.0 at frequencies near 1.4 GHz, observed with the Australia Telescope Compact Array. By applying rotation measure (RM) synthesis to the data, a pixel-by-pixel map of
Faraday rotation has been produced for the entire remnant. We find G296.5+10.0 to have a highly ordered RM structure, with mainly positive RMs (mean RM of +28 rad/m**2) on the eastern side and negative RMs (mean RM of -14 rad/m**2) on the western side, indicating a magnetic field which is directed away from us on one side and toward us on the other. We consider several possible mechanisms for creating the observed RM pattern. Neither Faraday rotation in foreground interstellar gas nor in a homogeneous ambient medium swept up by the SNR shell can easily explain the magnitude and sign of the observed RM pattern. Instead, we propose that the observed RMs are the imprint of an azimuthal magnetic field in the stellar wind of the progenitor star. Specifically, we calculate that a swept-up magnetized wind from a red supergiant can produce RMs of the observed magnitude, while the azimuthal pattern of the magnetic field at large distances from the star naturally produces the anti-symmetric RM pattern observed. Expansion into such a wind can possibly also account for the striking bilateral symmetry of the SNRs radio and X-ray morphologies.
Radio continuum emission from the supernova remnant G296.5+10.0 was observed using the Australia Telescope Compact Array. Using a 104 MHz bandwidth split into 13 x 8 MHz spectral channels, it was possible to produce a pixel-by-pixel image of Rotation
Measure (RM) across the entire remnant. A lack of correlation between RM and X-ray surface brightness reveals that the RMs originate from outside the remnant. Using this information, we will characterise the smooth component of the magnetic field within the supernova remnant and attempt to probe the magneto-ionic structure and turbulent scale sizes in the ISM and galactic halo along the line-of-sight.
