An all-sky survey of circular polarization at 200 MHz

We present results from the first all-sky radio survey in circular polarization. The survey uses the Murchison Widefield Array (MWA) to cover 30 900 sq deg, over declinations south of +30 degrees and north of -86 degrees centred at 200 MHz (over a 169-231 MHz band). We achieve a spatial resolution of similar to 3 arcmin 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 polarization by an order of magnitude. In a blind survey of the imaged region, we detect 14 pulsars in circular polarization 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 per cent 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.