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8th of September 2022
An all-sky survey of circular polarisation at 200 MHz
by Lenc et al.
The first all-sky survey in circular polarisation was conducted by Lenc et al. The survey utilised the unique wide-field capabilities of the Murchison Widefield Array (MWA) together with newly developed processing techniques to survey 30,900 square degrees of the southern sky at 200 MHz with a resolution of 3 arc-minutes. While circularly polarised emission is not prominent in most astrophysical sources there are a few classes of objects where a significant proportion of the observed emission is circularly polarised, e.g., pulsars, flare stars and exoplanets. By effectively filtering out all other sources of emission, observations in circular polarisation provide a convenient means to survey these source classes. The cut-out image shown above, which is about 1000 square degrees in size, would normally be dominated by intense emission from the Galactic plane, however, in circular polarisation the image is dominated by emission from two pulsars (circled in red). In all, a total of 33 pulsars and two flaring stars were detected. Six "transient" sources were also detected, however these were found to be associated with interloping communication satellites (an artificial source of circularly polarised emission). The success of the survey demonstrated that similar surveys that probe deeper and/or at longer wavelengths are warranted. The more recent discovery of an LMC pulsar as a circularly polarized ASKAP source by Wang et al. is further demonstration of the utility of circular polarisation studies.

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