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10th of July 2023
The mid-band Rapid ASKAP Continuum Survey
by Duchesne et al.
ASKAP is surveying the sky in three frequency bands across its operational frequency range. The first pass of the Rapid ASKAP Continuum Survey (RACS) at 887.5 MHz, "RACS-low", was completed in 2020. Duchesne et al. now present the second observing pass at 1367.5 MHz, "RACS-mid", which covers the whole sky south of a declination of +49 degrees. RACS-mid was observed at 1295.5 MHz using the full 288 MHz instantaneous bandwidth, however due to significant and persistent broadband radio frequency interference (RFI) in the lower half of the band, primarily due to Global Navigation System Satellites, the RACS-mid data are restricted to a bandwidth of 144 MHz, with a resulting central frequency of 1367.5 MHz.

The arrangement of ASKAP's 36 beams for observing is referred to as the beam footprint. RACS-low used the "square_6x6" footprint, however, the "closepack36" footprint was used for RACS-mid in order to achieve a more uniform sensitivity across the footprint. The image above shows representative RACS-mid closepack36 PAF footprint layout and shape. The coloured solid contours indicate 50% attenuation for a particular beam, and the faint, dashed contour indicates 12% (i.e., apparent brightness is attenuated to 12% of the sky brightness). The light grey contours correspond to the RACS-low square_6x6 footprint for comparison (solid, 50%; dotted, 12%). The black star indicates the centre of the footprint. The beams near the centre of the PAF are quite circular, but the outer beams are slightly elliptical.

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