Astronomy:Australian Square Kilometre Array Pathfinder

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Australian Square Kilometre Array Pathfinder
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The ASKAP radio telescope is a radio telescope array located at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory in the Mid West region of Western Australia. Construction started in 2009 and was completed in 2019, when the major Survey Science projects started. The Survey Science Projects are expected to be completed by 2030.

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.

ASKAP observes three classes of projects:

  1. Survey Science Projects, for which the telescope was primarily designed. These occupy at least 75% of the observing time
  2. Observatory projects which are projects run by the observatory for the benefit of the broader commeunity. All data from these are made publicly available without any proprietary period.
  3. Guest Science projects, which are proposed by users through the normal Australia Telescope National Facility proposal process

Description

Development and construction of ASKAP was led by CSIRO Space and Astronomy, 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
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 observatory to a supercomputer (acting as a radio correlator) at the Pawsey Supercomputing Research 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 full operation, at least 75% of its observing time are 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.

Eight (initially ten) ASKAP Survey Science Projects were selected to be the main focus of the observing, and they occupy at least 75% of the observing time.[13] They are:

Highest priority

Lower priority

  • 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]

Observatory Projects

Rapid ASKAP Continuum Survey (RACS)

From 2019 onwards, 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, but shallower than EMU which will take longer to complete. All the resulting data, including images, catalogues, and calibrated visibilities, are placed in the public domain.

The survey initially mapped three million galaxies in 300 hours, a million of which are new.[23][24]

RACS consists of three sub-projects:

  1. RACS-low, centred on 887.5 MHz, with a resolution of about 18 * 12 arcsec.[23][24]
  2. RACS-mid, centred on 1367.5 MHz, with a resolution of about 10 * 8 arcsec.[25]
  3. RACS-high, centred on 1655.5 MHz, with a resolution of about 9 * 6 arcsec.[26]

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).[27] 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

  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


Early science

From 2015 until 2019, a series of ASKAP Early Science Projects[28] 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.

Full survey operations

The ten Science Survey projects started observing in 2020, and are exepcted to be complete by 2030.

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.[29][30]

In 2021, during the ASKAP EMU Pilot Survey, a new class of astronomical object called Odd radio circles (ORCs) were discovered at ASKAP.[31][32]

See also

References

  1. ↑ "SKA Factsheet for Journalists". SKA Project Development Office (SPDO). Skatelescope.org. http://www.skatelescope.org/wp-content/uploads/2011/03/SKA_Factsheet-for-Journalist_web.pdf. 
  2. ↑ "Report of the SKA Siting Options Working Group". SKA Organisation. Skatelescope.org. 14 June 2012. http://www.skatelescope.org/uploaded/19942_120520_SOWG.Report.pdf. 
  3. ↑ "The Australia Telescope National Facility". CSIRO. http://www.atnf.csiro.au/the_atnf/. 
  4. ↑ 4.0 4.1 "ASKAP Fast Facts". CSIRO. http://www.atnf.csiro.au/projects/askap/ASKAP_Overview.pdf. 
  5. ↑ Fingas, Jon (5 October 2012). "Australia Square Kilometre Array Pathfinder goes live as the world's quickest radio telescope". Engadget. https://www.engadget.com/2012/10/05/australia-square-kilometre-array-pathfinder-goes-live/. 
  6. ↑ "ASKAP News". Atnf.csiro.au. 18 June 2012. http://www.atnf.csiro.au/projects/askap/news_antenna_18062012.html. 
  7. ↑ "Murchison Radio-astronomy Observatory". CSIRO. http://www.atnf.csiro.au/projects/askap/site.html. 
  8. ↑ Redfern, Martin (31 March 2011). "World's biggest radio telescope, Square Kilometre Array". BBC News. https://www.bbc.co.uk/news/science-environment-12891215. 
  9. ↑ "Pawsey Centre". iVEC. 14 June 2012. http://www.ivec.org/ivec-projects/pawsey/. 
  10. ↑ "ASKAP Science Update, Vol. 5". CSIRO. http://www.atnf.csiro.au/projects/askap/ASKAP_Science_Update_5.pdf. 
  11. ↑ CSIRO (8 October 2020). "ASKAP Survey Science projects". https://www.atnf.csiro.au/projects/askap/science.html. 
  12. ↑ "ASKAP Science". CSIRO. http://www.atnf.csiro.au/projects/askap/science.html. 
  13. ↑ "CSIRO sets science path for new telescope". CSIRO. http://www.csiro.au/news/CSIRO-sets-path-for-ASKAP.html. 
  14. ↑ "EMU: Evolutionary Map of the Universe". Atnf.csiro.au. 7 November 2008. http://www.atnf.csiro.au/people/rnorris/emu/. 
  15. ↑ Norris, Ray (2011). "EMU:THe Evolutionary Map of the Universe". Publications of the Astronomical Society of Australia 28 (3): 215–248. doi:10.1071/AS11021. Bibcode: 2011PASA...28..215N. 
  16. ↑ "WALLABY – the ASKAP HI All-Sky Survey". Atnf.csiro.au. http://www.atnf.csiro.au/research/WALLABY/. 
  17. ↑ Koribalski, Barbel (2020). "WALLABY - an SKA Pathfinder HI survey". Astrophysics and Space Science 365 (7): 118. doi:10.1007/s10509-020-03831-4. Bibcode: 2020Ap&SS.365..118K. 
  18. ↑ "DINGO". Internal.physics.uwa.edu.au. http://internal.physics.uwa.edu.au/~mmeyer/dingo/welcome.html. 
  19. ↑ "Sydney Institute for Astronomy – The University of Sydney". Physics.usyd.edu.au. 15 September 2011. http://www.physics.usyd.edu.au/sifa/Main/FLASH/. 
  20. ↑ "GASKAP". https://sites.google.com/site/gaskapproject/home. 
  21. ↑ "ASKAP POSSUM – Home Page". Physics.usyd.edu.au. 24 August 2012. http://www.physics.usyd.edu.au/sifa/possum/. 
  22. ↑ "VAST: Variables and Slow Transients: Main – Home Page browse". Physics.usyd.edu.au. http://www.physics.usyd.edu.au/sifa/vast/index.php. 
  23. ↑ 23.0 23.1 "Australian scientists map millions of galaxies with new telescope". BBC News. November 30, 2020. https://www.bbc.com/news/world-australia-55139976. 
  24. ↑ 24.0 24.1 McConnell, D. et al. (2020). "The Rapid ASKAP Continuum Survey I: Design and first results". Publications of the Astronomical Society of Australia 37: E048. doi:10.1017/pasa.2020.41. Bibcode: 2020PASA...37...48M. 
  25. ↑ Duchesne, S. W.; Grundy, J. A.; Heald, George H.; Lenc, Emil; Leung, James K.; McConnell, David; Murphy, Tara; Pritchard, Joshua et al. (2024). "The Rapid ASKAP Continuum Survey V: Cataloguing the sky at 1 367.5 MHz and the second data release of RACS-mid" (in en). Publications of the Astronomical Society of Australia 41. doi:10.1017/pasa.2023.60. ISSN 1323-3580. https://www.cambridge.org/core/product/identifier/S1323358023000607/type/journal_article. 
  26. ↑ Duchesne, S. W.; Ross, K.; Thomson, A. J. M.; Lenc, E.; Murphy, Tara; Galvin, T. J.; Hotan, A. W.; Moss, V. et al. (2025). "The Rapid ASKAP Continuum Survey (RACS) VI: The RACS-high 1 655.5 MHz images and catalogue" (in en). Publications of the Astronomical Society of Australia 42. doi:10.1017/pasa.2025.2. ISSN 1323-3580. https://www.cambridge.org/core/product/identifier/S1323358025000025/type/journal_article. 
  27. ↑ 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. doi:10.1017/pasa.2016.37. Bibcode: 2016PASA...33...42M. 
  28. ↑ Ball, Lewis (7 September 2015). "ASKAP Early Science program". https://www.atnf.csiro.au/projects/askap/ASKAP_EarlyScienceProgram.pdf. 
  29. ↑ Slezak, Michael; Timms, Penny (27 May 2020). "Half the matter in the universe was missing. Australian scientists just found it" (in en-AU). ABC News (on-line) (Australian Broadcasting Corporation). https://www.abc.net.au/news/2020-05-28/astronomers-find-universe-missing-matter/12291788. 
  30. ↑ MacQuart, J.-P.; Prochaska, J. X.; McQuinn, M.; Bannister, K. W.; Bhandari, S.; Day, C. K.; Deller, A. T.; Ekers, R. D. et al. (2020). "A census of baryons in the Universe from localized fast radio bursts". Nature 581 (7809): 391–395. doi:10.1038/s41586-020-2300-2. PMID 32461651. Bibcode: 2020Natur.581..391M. 
  31. ↑ Osborne, Hannah (9 July 2020). "'Odd' Circles of Radio Waves Coming from Unknown Cosmic Source Discovered". Newsweek. https://www.newsweek.com/circle-radio-waves-space-source-unknown-1516549. 
  32. ↑ Norris, Ray (2021). "Unexpected circular radio objects at high Galactic latitude". Publications of the Astronomical Society of Australia 38: e003. doi:10.1017/pasa.2020.52. Bibcode: 2021PASA...38....3N. 



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