GLEAM: The GaLactic and Extragalactic All-sky MWA survey

TL;DR

GLEAM is an extensive radio sky survey using the Murchison Widefield Array, covering frequencies 72-231 MHz, providing detailed imaging, sensitivity analysis, and addressing observational challenges over two years.

Contribution

This paper introduces the GLEAM survey methodology, data acquisition strategies, and sensitivity analysis, highlighting improvements in wide-field radio imaging at low frequencies.

Findings

Achieved ~2.5 arcmin resolution at 154 MHz

Provided sensitivity estimates for different observing setups

Addressed ionospheric and instrumental polarization challenges

Abstract

GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of the entire radio sky south of declination +25 deg at frequencies between 72 and 231 MHz, made with the Murchison Widefield Array (MWA) using a drift scan method that makes efficient use of the MWA's very large field-of-view. We present the observation details, imaging strategies and theoretical sensitivity for GLEAM. The survey ran for two years, the first year using 40 kHz frequency resolution and 0.5 s time resolution; the second year using 10 kHz frequency resolution and 2 s time resolution. The resulting image resolution and sensitivity depends on observing frequency, sky pointing and image weighting scheme. At 154 MHz the image resolution is approximately 2.5 x 2.2/cos(DEC+26.7) arcmin with sensitivity to structures up to ~10 deg in angular size. We provide tables to calculate the expected thermal noise for GLEAM mosaics depending on pointing and frequency and discuss limitations to achieving theoretical noise in Stokes I images. We discuss challenges, and their solutions, that arise for GLEAM including ionospheric effects on source positions and linearly polarised emission, and the instrumental polarisation effects inherent to the MWA's primary beam.