The Murchison Widefield Array (MWA) is a joint project between an international consortium of organisations to construct and operate a low-frequency radio array. "Widefield" refers to its very large field of view (on the order of 30 degrees across). Operating in the frequency range 70–300 MHz, the main scientific goals of the MWA are to detect neutral atomic hydrogen emission from the cosmological Epoch of Reionization (EoR), to study the Sun, the heliosphere, the Earth's ionosphere, and radio transient phenomena, as well as map the extragalactic radio sky. It is located at the Murchison Radio-astronomy Observatory (MRO). Along with the Australian Square Kilometre Array Pathfinder (ASKAP), also at the MRO, and two radio telescopes in South Africa, the Hydrogen Epoch of Reionization Array (HERA) and MeerKAT, the MWA is one of four precursors to the international project known as the Square Kilometre Array (SKA).
Development The MWA was to be situated at Mileura Station where initial testing had been conducted then moved southwest to Boolardy Station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO), 800 kilometres (500 mi) north of Perth. This location offers a quiet radio environment and stable climate for observations. The MRO is also the site of CSIRO's Australian Square Kilometre Array Pathfinder (ASKAP) and one of two selected sites in Australia for the Square Kilometre Array (SKA). In addition to the geographic link, the MWA is one of four official SKA precursor telescopes – instruments that provide instrumental, scientific and operational information to help guide SKA developments, along with two sites in South Africa, HERA and MeerKAT. The MWA was initially conceived as a 512-tile instrument (512T) to be built in stages. The first stage was a 32-tile prototype (MWA-32T), which was constructed and operated with increasing capability over the period 2007–2011, testing telescope hardware and making preliminary science observations, including initial observations of EoR fields. The first phase of the telescope, the so-called "Phase I MWA", achieved full practical completion in late 2012 and completed commissioning on 20 June 2013, before moving into full operations. The Phase I MWA fully cross-correlates signals from 128 phased tiles, each of which consist of 16 crossed dipoles arranged in a 4×4 square. As part of a planned future rollout, infrastructure on-site at the MRO was installed during Phase I to allow an eventual build-out to 256 tiles. The total cost of the first phase of the project was A$51 million. In 2017 the telescope received the planned upgrade, doubling the number of antennas, resulting in an increase in both resolution and sensitivity. This upgraded instrument is known as the "Phase II MWA". Phase II was practically completed in October 2017 and officially launched on 23 April 2018. Installation of the additional antennas and commissioning of the array was led by the third MWA director, Randall Wayth, while operations of the Phase II instruments have been led by the fourth director, Melanie Johnston-Hollitt. The third phase of the project commenced in 2022 with the addition of the MWAX correlator. This was followed by instrumentation upgrades through to 2025, with the deployment of a new fleet of digital receivers, designed and built by the MWA Collaboration, led by current MWA director Steven Tingay. These receivers complement existing receivers, such that the MWA now supports the full correlation of all 256 MWA antenna tiles. This upgrade, known as 'Phase III' of the MWA, means that the maximum instantaneous sensitivity of the MWA is doubled and the data output of the telescope is quadrupled, providing a clearer and more expansive view of the universe.
Science The MWA is an inherently versatile instrument with a very large field of view, on the order of 30 degrees across, able to cover a wide range of scientific goals. In Phase I the array provided a wealth of scientific papers covering topics such as detection of H II region(s) in the Galactic plane, limits on radio emission from extra-solar planets, observations of haloes and relics in galaxy clusters to detection of transient radio sources and space debris tracking. Two of the most significant results from the Phase I MWA were:
The first detection of plasma tubes in the ionosphere by undergraduate student Cleo Loi. Loi won the Astronomical Society of Australia 2015 Bok Prize for her research. The "Galactic and Extragalactic All-sky MWA" (or "GLEAM") is a survey of 300,000 extragalactic sources at 20 frequencies between 70 and 230 MHz that was carried out by the MWA. A second survey, GLEAM-X, was run for 113 nights from 2018 to 2020.
Discoveries In January 2022, a team led by Dr Natasha Hurley-Walker of Curtin University re-analyzed 2018 GLEAM data and announced in Nature that object GLEAM-X J162759.5−523504.3 is a long-period (1,091.170 second / 18m11s) object, that provided a bright pulse of energy for up to a minute, and is some 4,000 light-years from Earth in the Milky Way galaxy. The derived position is in the constellation Norma at right ascension 16h 27m 59.5s, declination −52°35′04.3". The object produces pulses at 154MHz of peak flux densities of up to S154MHz = 45 Jy. Scaling this to 1.4 GHz would indicate S1.4 GHz = 3.5 Jy and, therefore, a luminosity L1.4 GHz = 4×10^31ergs−1. It is speculated to be similar to a pulsar or magnetar. The object was discovered by Tyrone O'Doherty as part of his undergraduate honours project supervised by Dr Hurley-Walker.
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