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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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