An all-sky survey of circular polarisation at 200 MHz

We present results from the first all-sky radio survey in circular polarisation. The survey uses the Murchison Widefield Array (MWA) to cover 30900 sq. deg., over declinations south of +30\(^{\circ}\) and north of -86\(^{\circ}\) centred at 200 MHz (over a 169-231 MHz band). We achieve a spatial resolution of approx. 3' and a typical sensitivity of 3.0 mJy PSF\(^{-1}\) over most of the survey region. We demonstrate a new leakage mitigation technique that reduces the leakage from total intensity into circular polarisation by an order of magnitude. In a blind survey of the imaged region, we detect 14 pulsars in circular polarisation above a 6\(\sigma\) threshold. We also detect six transient sources associated with artificial satellites. A targeted survey of 2376 pulsars within the surveyed region yielded 33 detections above \(4\sigma\). Looking specifically at pulsars previously detected at 200 MHz in total intensity, this represents a 35% detection rate. We also conducted a targeted survey of 2400 known flare stars, this resulted in two tentative detections above \(4\sigma\). A similar targeted search for 1506 known exoplanets in the field yielded no detections above \(4\sigma\). The success of the survey suggests that similar surveys at longer wavelength bands and of deeper fields are warranted.