GaLactic and Extragalactic All-Sky MWA-eXtended (GLEAM-X) survey: Pilot observations

This proposal is a pilot study for the extension of the highly successful GaLactic and Extragalactic MWA (GLEAM) survey (Wayth et al. 2015). The aim is to test out new observing strategies and data reduction techniques suitable for exploiting the longer baselines of the extended phase 2 MWA array. Deeper and wide surveys at higher resolution will enable a legion of science capabilities pertaining to galaxy evolution, clusters and the cosmic web, whilst maintaining the advantages over LOFAR including larger field-of-view, wider frequency coverage and better sensitivity to extended emission. We will continue the successful drift scan mode observing to test the feasibility of a large-area survey in 2017-B and onward. We will also target a single deep area with a bright calibrator source to establish the utility of focussed deep observations. In both cases, we will be exploring calibrating and imaging strategies across 72-231 MHz with the new long baselines. The published extragalactic sky catalogue (Hurley-Walker et al. 2017) improves the prospects for good ionospheric calibration in this new regime, as well as trivialising flux calibration. The new Alternative Data Release of the TIFR GMRT Sky Survey (TGSS-ADR1; Intema et al. 2016), which has 30" resolution and covers the proposed observing area, allows us to test whether our calibration and imaging strategy correctly recovers the true structure of (high surface-brightness) resolved sources. GLEAM-X will have lower noise, higher surface brightness sensitivity, and have considerably wider bandwidth than TGSS. These properties will enable a wide range of science, such as: Detecting and characterising cluster relics and haloes beyond z=0.45; Accurately determining radio source counts at multiple frequencies; Measuring the low-v luminosity function to z 0.5; Performing Galactic plane science such as HII region detection and cosmic tomography; Determining the typical ionospheric diffractive scale at the MRO, feeding into SKA_Low calibration strategies. In addition the proposal is designed to be commensally used for transients science, and will also create a more accurate, higher-resolution foreground model for the EoR2 field, allowing better foreground subtraction and therefore increased sensitivity to the EoR signal.