Astronomy:Murchison Widefield Array

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Murchison Widefield Array
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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[1] 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.[2] The MRO is also the site of CSIRO's Australian Square Kilometre Array Pathfinder[3] (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.[4]

The MWA was initially conceived as a 512-tile instrument (512T)[5] 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.[6]

The first phase of the telescope, the so-called "Phase I MWA", achieved full practical completion in late 2012[7] 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.[8]


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.[9] Loi won the Astronomical Society of Australia 2015 Bok Prize for her research.[10][9]
  • 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.[11][12]

A second survey, GLEAM-X, was run for 113 nights from 2018 to 2020.[13]

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.[14]

System overview

Project partners

During Phase I, the MWA consortium initially comprised 110 individual researchers drawn from 12 institutions from Australia, New Zealand, the United States and India. New Zealand joined the consortium in late 2011 and an additional two institutions from the United States were added in 2014 taking the total number of Phase I partner organizations to 14. By the end of Phase I there were 160 individual research scientists involved in the MWA.

Membership of the MWA consortium was substantially expanded for Phase II with the admission of Canada, China and Japan, though India left the consortium at this time. Nevertheless, at the start of Phase II the MWA had expanded to 21 partner organizations across six countries and had a membership of 270 individual scientists. The expansion of the collaboration was largely the work of the then MWA Board Chair (January 2014 – January 2018) and past MWA director, Melanie Johnston-Hollitt.

By 2024 the consortium had increased its partner organisations significantly, with the addition of Switzerland, and a total of 30 partner organisations across six countries and a membership of 243 individual scientists.


Funding for the MWA to date has been provided by partner institutions and by allocations from national funding agencies: the New Zealand Ministry of Economic Development (now the Ministry of Business, Innovation and Employment), the United States National Science Foundation, the Australian Research Council (ARC), the Australian National Collaborative Research Infrastructure Strategy (NCRIS) administered by Astronomy Australia Ltd., and the Australia-India Strategic Research Fund Overview (AISRF). In addition, support for the MWA computer hardware was given through an IBM Shared University Research Grant awarded to Victoria University of Wellington and Curtin University (PIs: Johnston-Hollitt and Tingay).

See also

References

  1. ↑ "Murchison Widefield Array". MIT Haystack Observatory. 2013. http://www.haystack.mit.edu/mwa/. 
  2. ↑ The MWA Site in Western Australia . Murchison Widefield Array. Retrieved on 2 December 2012.
  3. ↑ Square Kilometre Array. CSIRO. Retrieved on 2 December 2012.
  4. ↑ "Precursors and Pathfinders". https://www.skatelescope.org/precursors-pathfinders-design-studies/. 
  5. ↑ (May 2011). The Murchison Widefield Array (MWA): Current Status and Plans. American Astronomical Society. Retrieved on 2 December 2012.
  6. ↑ (May 2011). MWA Observations of Candidate EoR Fields. Bulletin of the American Astronomical Society, Vol. 43. American Astronomical Society. Retrieved on 2 December 2012.
  7. ↑ We did it!. Adventures in Astronomy. Retrieved on 2 December 2012.
  8. ↑ "Australia unveils telescope to warn of solar flares". The Raw Story (Raw Story Media). 1 December 2012. https://www.rawstory.com/2012/12/australia-unveils-telescope-to-warn-of-solar-flares/. 
  9. ↑ 9.0 9.1 How an undergraduate discovered tubes of plasma in the sky, Tara Murphy, The Conversation, 5 June 2015, accessed 7 June 2015
  10. ↑ Sydney University physics undergraduate maps huge plasma tubes in the sky, Marcus Strom, The Sydney Morning Herald, 1 June 2015, accessed 8 June 2015
  11. ↑ "MWA – GLEAM Survey". MWA. http://www.mwatelescope.org/science/gleam-survey. 
  12. ↑ "GLEAM". ICRAR. 24 October 2016. http://www.icrar.org/gleam/. 
  13. ↑ Milky Way Galaxy Radio Survey Reveals Stunning New Image
  14. ↑ A radio transient with unusually slow periodic emission, N. Hurley-Walker et al, Nature, 601, pages 526–530 (2022), https://doi.org/10.1038/s41586-021-04272-x 2022-01-27



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