Australian Square Kilometre Array Pathfinder

The Australian Square Kilometre Array Pathfinder (ASKAP) is a radio telescope array located at Murchison Radio-astronomy Observatory (MRO) in the Mid West region of Western Australia.

Australian Square Kilometre Array Pathfinder
Antennas of the ASKAP telescope at the Murchison Radio-astronomy Observatory in Western Australia
Part ofAustralia Telescope National Facility
Murchison Radio-astronomy Observatory
Square Kilometre Array Edit this on Wikidata
Location(s)Western Australia, AUS
Coordinates26°41′46″S 116°38′13″E
OrganizationCSIRO Edit this on Wikidata
Telescope styleradio interferometer Edit this on Wikidata
Websitewww.atnf.csiro.au/projects/askap/
Australian Square Kilometre Array Pathfinder is located in Australia
Australian Square Kilometre Array Pathfinder
Location of Australian Square Kilometre Array Pathfinder
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The facility began as a technology demonstrator for the international Square Kilometre Array (SKA), an internationally planned radio telescope which will be larger and more sensitive.[1] The ASKAP site has been selected as one of the SKA's two central locations.[2]

It is operated by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and forms part of the Australia Telescope National Facility.[3] Construction commenced in late 2009 and first light was in October 2012.[4][5]

ASKAP consists of 36 identical parabolic antennas, each 12 m (39 ft) in diameter, working together as a single astronomical interferometer with a total collecting area of approximately 4,000 m2 (43,000 sq ft). Each antenna is equipped with a phased-array feed (PAF), significantly increasing the field of view. This design provides both fast survey speed and high sensitivity.

Description

Development and construction of ASKAP was led by CSIRO Astronomy and Space Science (CASS), in collaboration with scientists and engineers in the Netherlands, Canada, and the US, as well as colleagues from Australian universities and industry partners in China.[4]

Design
External video
video icon Watch a video of the first ASKAP antenna construction at the MRO in January 2010.

The construction and assembly of the dishes was completed in June 2012.[6]

ASKAP was designed as a synoptic telescope with a wide field-of-view, large spectral bandwidth, fast survey speed, and a large number of simultaneous baselines.[7] The greatest technical challenge was the design and construction of the phased array feeds, which had not previously been used for radio astronomy, and so presented many new technical challenges, as well as the largest data rate so far encountered in a radio telescope.

Installation of an advanced Phased Array Feed (PAF) receiver on an ASKAP antenna. This feed includes 188 individual receivers, to greatly extend the Field of View of an ASKAP 12m dish to 30 square degrees.

ASKAP is located in the Murchison district in Western Australia, a region that is extremely "radio-quiet" due to the low population density and resulting lack of radio interference (generated by human activity) that would otherwise interfere with weak astronomical signals.[8] The radio quiet location is recognised as a natural resource and protected by the Australian Commonwealth and Western Australia State Government through a range of regulatory measures.

Data from ASKAP are transmitted from the MRO to a supercomputer (acting as a radio correlator) at the Pawsey Supercomputing Centre in Perth.[9] The data are processed in near-real-time by a pipeline processor running purpose-built software.[10] All data are made publicly available after quality checks by the ten ASKAP Survey Science Teams.

Survey science projects
The array in 2010

During ASKAP's first five years of full operation, at least 75% of its observing time will be used for large Survey Science Projects[11] ASKAP is intended to study the following topics:[12]

  1. Galaxy formation and gas evolution in the nearby Universe through extragalactic HI surveys
  2. Evolution, formation and population of galaxies across cosmic time via high resolution, continuum surveys
  3. Characterisation of the radio transient sky through detection and monitoring (including VLBI) of transient and variable sources, and
  4. Evolution of magnetic fields in galaxies over cosmic time through polarisation surveys.

Ten ASKAP Survey Science Projects have been selected to run in the first five years of operations.[13] They are:

Highest priority

Lower priority
  • COAST: Compact Objects with ASKAP: Surveys and Timing
  • CRAFT: The Commensal Real-time ASKAP Fast Transients survey
  • DINGO: Deep Investigations of Neutral Gas Origins[18]
  • FLASH: The First Large Absorption Survey in HI[19]
  • GASKAP: The Galactic ASKAP Spectral Line Survey[20]
  • POSSUM: Polarization Sky Survey of the Universe's Magnetism[21]
  • VAST: An ASKAP Survey for Variables and Slow Transients[22]
  • VLBI: The High Resolution Components of ASKAP: Meeting the Long Baseline Specifications for the SKA

Construction and operational phases

Construction

Construction of ASKAP started in 2009.

Boolardy Engineering Test Array

Once six antennas were completed and equipped with phased-array feeds, and backend electronics, the array was named the Boolardy Engineering Test Array (BETA).[23] BETA operated from March 2014 to February 2016. It was the first aperture synthesis radio telescope to use phased array feed technology, enabling the formation of up to nine dual-polarisation beams. A series of astronomical observations were made with BETA to test the operation of the phased array feeds, and to help the commissioning and operation of the final ASKAP telescope.

Design enhancement

The first prototype phased-array feeds (PAF) proved the concept worked, but their performance was not optimum. In 2013–2014, while the BETA array was operational, significant sections of ASKAP were redesigned to improve performance in a process known as the ASKAP design enhancement (ADE). The main changes were:

  1. Improve the receiver design to provide a lower system temperature that would be roughly constant across the bandwidth of the receivers
  2. Replace the FPGA chips in the digital processor to faster chips with lower power consumption
  3. Replace the water cooling system in the PAF by a more reliable Peltier temperature stabilisation system
  4. Replace the coaxial signal transmission between the antennas and the central site by a system in which the radio frequency signals were directly modulated onto optical signals to be transmitted over optical fibre
  5. Replace the complex radio-frequency signal conversion system by a direct sampling system

Although the ADE delayed the completion of ASKAP, this was felt to be justified as the resulting system had better performance, was lower cost, and more reliable. The first ADE PAF was installed in August 2014. By April 2016, nine ADE PAFs were installed, together with the new ADE correlator, and more PAFs were progressively installed on the remaining antennas over the next few years.

Early science

From 2015 until 2019, a series of ASKAP Early Science Projects[24] were observed on behalf of the astronomical community, across all areas of astrophysics, with the primary goals of demonstrating the capabilities of ASKAP, providing data to the astronomy community to facilitate development of techniques, and evaluating the performance and characteristics of the system. The early science program resulted in several science papers published in peer-reviewed journals, as well as helping to commission the instrument, and guiding the planning of the main survey projects.

Pilot surveys

Each of the ten Science Survey projects were invited to submit a proposal for a pilot survey to test observing strategies. These pilot survey observations took place in 2019-2020 and have resulted in significant astrophysical results, including the discovery of Odd Radio Circles.

Rapid ASKAP Continuum Survey (RACS)

From 2019 to 2020, ASKAP conducted a rapid survey of the entire sky up to declination +40°, to provide a shallow model of the radio sky to aid the calibration of subsequent deep ASKAP surveys, as well as providing a valuable resource to astronomers. With a typical rms sensitivity of 0.2-0.4 mJy/beam and a typical spatial resolution of 15-25 arcsec, RACS is significantly deeper, and higher resolution, than comparable radio surveys such as NVSS and SUMMS. All the resulting data will be placed in the public domain.

The survey mapped three million galaxies in 300 hours, a million of which are new.[25][26]

Full survey operations

The ten Science Survey projects are expected to start observing in 2022, although there may be some adjustment and realignment of the projects before that date.

Discoveries

In May 2020, astronomers announced a measurement of the intergalactic medium using six fast radio bursts observed with ASKAP; their results confirm existing measurements of the missing baryon problem.[27][28]

Odd radio circles (ORCs) are a possible "new class of astronomical object" discovered at ASKAP.[29]

See also
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References
  1. "SKA Factsheet for Journalists" (PDF). SKA Project Development Office (SPDO). Skatelescope.org. Retrieved 13 April 2011.
  2. "Report of the SKA Siting Options Working Group" (PDF). SKA Organisation. Skatelescope.org. 14 June 2012.
  3. "The Australia Telescope National Facility". CSIRO. Retrieved 13 April 2011.
  4. "ASKAP Fast Facts" (PDF). CSIRO. Retrieved 13 April 2011.
  5. Fingas, Jon (5 October 2012). "Australia Square Kilometre Array Pathfinder goes live as the world's quickest radio telescope". Engadget. Retrieved 7 October 2012.
  6. "ASKAP News". Atnf.csiro.au. 18 June 2012. Retrieved 18 January 2013.
  7. "Murchison Radio-astronomy Observatory". CSIRO. Retrieved 13 April 2011.
  8. Redfern, Martin (31 March 2011). "World's biggest radio telescope, Square Kilometre Array". BBC News. Retrieved 13 April 2011.
  9. "Pawsey Centre". iVEC. 14 June 2012. Archived from the original on 7 March 2013.
  10. "ASKAP Science Update, Vol. 5" (PDF). CSIRO. Retrieved 13 April 2011.
  11. CSIRO (8 October 2020). "ASKAP Survey Science projects".
  12. "ASKAP Science". CSIRO. Retrieved 8 November 2010.
  13. "CSIRO sets science path for new telescope". CSIRO. Archived from the original on 19 March 2011. Retrieved 13 April 2011.
  14. "EMU: Evolutionary Map of the Universe". Atnf.csiro.au. 7 November 2008. Retrieved 18 January 2013.
  15. Norris, Ray (2011). "EMU:THe Evolutionary Map of the Universe". Publications of the Astronomical Society of Australia. 28 (3): 215–248. arXiv:1106.3219. Bibcode:2011PASA...28..215N. doi:10.1071/AS11021. S2CID 2289252.
  16. "WALLABY – the ASKAP HI All-Sky Survey". Atnf.csiro.au. Retrieved 18 January 2013.
  17. Koribalski, Barbel (2020). "WALLABY - an SKA Pathfinder HI survey". Astrophysics and Space Science. 365 (7): 118. arXiv:2002.07311. Bibcode:2020Ap&SS.365..118K. doi:10.1007/s10509-020-03831-4. hdl:10566/5844. S2CID 211146706.
  18. "DINGO". Internal.physics.uwa.edu.au. Archived from the original on 7 June 2013. Retrieved 18 January 2013.
  19. "Sydney Institute for Astronomy – The University of Sydney". Physics.usyd.edu.au. 15 September 2011. Archived from the original on 21 April 2013. Retrieved 18 January 2013.
  20. "GASKAP". Retrieved 18 January 2013.
  21. "ASKAP POSSUM – Home Page". Physics.usyd.edu.au. 24 August 2012. Archived from the original on 12 October 2016. Retrieved 18 January 2013.
  22. "VAST: Variables and Slow Transients: Main – Home Page browse". Physics.usyd.edu.au. Retrieved 18 January 2013.
  23. McConnell, D. (2016). "The Australian Square Kilometre Array Pathfinder: Performance of the Boolardy Engineering Test Array". Publications of the Astronomical Society of Australia. 33: 042. arXiv:1608.00750. Bibcode:2016PASA...33...42M. doi:10.1017/pasa.2016.37. S2CID 53591261.
  24. Ball, Lewis (7 September 2015). "ASKAP Early Science program" (PDF). ASKAP Early Science. Retrieved 6 October 2020.
  25. "Australian scientists map millions of galaxies with new telescope". BBC News. 30 November 2020. Retrieved 1 December 2020.
  26. McConnell, D.; et al. (2020). "The Rapid ASKAP Continuum Survey I: Design and first results". Publications of the Astronomical Society of Australia. 37: E048. arXiv:2012.00747. Bibcode:2020PASA...37...48M. doi:10.1017/pasa.2020.41.
  27. Slezak, Michael; Timms, Penny (27 May 2020). "Half the matter in the universe was missing. Australian scientists just found it". ABC News (on-line). Australian Broadcasting Corporation. Retrieved 27 May 2020.
  28. MacQuart, J.-P.; Prochaska, J. X.; McQuinn, M.; Bannister, K. W.; Bhandari, S.; Day, C. K.; Deller, A. T.; Ekers, R. D.; James, C. W.; Marnoch, L.; Osłowski, S.; Phillips, C.; Ryder, S. D.; Scott, D. R.; Shannon, R. M.; Tejos, N. (2020). "A census of baryons in the Universe from localized fast radio bursts". Nature. 581 (7809): 391–395. arXiv:2005.13161. Bibcode:2020Natur.581..391M. doi:10.1038/s41586-020-2300-2. PMID 32461651. S2CID 218900828.
  29. Osborne, Hannah (9 July 2020). "'Odd' Circles of Radio Waves Coming from Unknown Cosmic Source Discovered". Newsweek. Retrieved 10 July 2020.
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