Description

The GLEAM survey covers the entire sky south of Dec +30. A description of the science motivations and survey methodology for GLEAM can be found in the GLEAM Survey definition paper by Wayth et al. (2015). As has been previously demonstrated in Hurley-Walker (2014), meridian drift scans are an effective surveying technique for the MWA and we re-use the basic strategy for GLEAM. The sky is divided into seven strips in Declination and five frequency ranges as summarised below. The Declinations are chosen such that the peak in the primary beam response for a given setting corresponds approximately to the half power point of the neighbouring beam along the meridian at 150 MHz.

The instantaneous frequency coverage of the MWA is 30.72 MHz, so the frequency range between 72 and 231 MHz is divided into five bands that provide near contiguous coverage, but avoid the band around 137 MHz that is contaminated by satellite interference. The observing was executed as a series of week-long campaigns where a single Declination setting is observed in a night, covering a strip between approximately 8 and 10 hours in length, depending on the time of year. The Sun can be bright and time-variable at MWA frequencies, so observations were only performed at night. Within a night, the observing was broken into a series of 120 s scans for each frequency, cycling through all five frequency settings over 10 minutes. Within a scan, typically 108 s of usable data were collected. Every 2 hours throughout the night, a calibration field was observed over all five frequency settings, again as a set of 120 s scans totalling 10 minutes.

GLEAM observing began in August 2013 and the first year concluded in July 2014. The second year of observing took data at HA +/- = 1 and concluded in July 2015. A bonus third year of observing at high (~250-310MHz) frequency was also performed, and concluded in July 2016.

Each Declination strip of GLEAM is calibrated using a single primary calibrator and then self-calibrated to remove residual amplitude and phase errors. The wide primary beam of the MWA is modelled and calibrated out, and the flux scale is tied to existing catalogues.