GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended (GLEAM-X) I: Survey description and initial data release

We describe a new low-frequency wideband radio survey of the southern sky. Observations covering 72-231MHz and Declinations south of +30(o) have been performed with the MurchisonWidefield Array "extended" Phase II configuration over 2018-2020 and will be processed to form data products including continuum and polarisation images and mosaics, multi-frequency catalogues, transient search data, and ionospheric measurements. From a pilot field described in this work, we publish an initial data release covering 1,447deg(2) over 4 h <= RA <= 13 h, -32.7(o) <= Dec <= -20.7.. We process twenty frequency bands sampling 72-231MHz, with a resolution of 2'-45", and produce a wideband source-finding image across 170-231MHz with a root mean square noise of 1.27 +/- 0.15 mJy beam(-1). Source-finding yields 78,967 components, of which 71,320 are fitted spectrally. The catalogue has a completeness of 98% at similar to 50 mJy, and a reliability of 98.2% at 5 sigma rising to 99.7% at 7 sigma. A catalogue is available from Vizier; images are made available via the PASA datastore, AAO Data Central, and SkyView. This is the first in a series of data releases from the GLEAM-X survey.