SKA (Square Kilometer Array)
SKA (Square Kilometer Array) Radio Telescopes
The SKA project is an international effort to build the world's largest radio telescope, with eventually over a square kilometer (one million square meters) of collecting area. The scale of the SKA represents a huge leap forward in both engineering and research & development towards building and delivering a unique instrument, with the detailed design and preparation now well under way. As one of the largest scientific endeavors in history, the SKA will bring together a wealth of the world's finest scientists, engineers and policy makers to bring the project to fruition. 1)
Background: The history of the SKA begin in September 1993 the International Union of Radio Science (URSI) established the Large Telescope Working Group to begin a worldwide effort to develop the scientific goals and technical specifications for a next generation radio observatory. 2)
Subsequent meetings of the working group provided a forum for discussing the technical research required and for mobilizing a broad scientific community to cooperate in achieving this common goal. In 1997, eight institutions from six countries (Australia, Canada, China, India, the Netherlands, and the USA) signed a Memorandum of Agreement to cooperate in a technology study program leading to a future very large radio telescope.
On August 10, 2000, at the International Astronomical Union meeting in Manchester, UK, a Memorandum of Understanding to establish the ISSC (International Square Kilometer Array Steering Committee) was signed by representatives of eleven countries (Australia, Canada, China, Germany, India, Italy, the Netherlands, Poland, Sweden, the United Kingdom, and the United States).
This was superseded by a Memorandum of Agreement to Collaborate in the Development of the Square Kilometer Array which came into force on 1 January 2005 and which has been extended until 31 December 2007. This made provision for the expansion of the Steering Committee to 21 members (7 each for Europe, USA, and the Rest of the World) and the establishment of the International SKA Project Office.
In 2007, owing to a proposed expansion of the ISPO (International SKA Project Office), the ISSC called for proposals to host the Project Office. Three proposals were received, and following extensive discussion, the ISSC selected the University of Manchester as the host organization for the Project Office. A Memorandum of Agreement between the ISSC and the University of Manchester was signed in October 2007. The Project Office moved to the new Alan Turing building in Manchester, also home to the Jodrell Bank Center for Astrophysics, on 1 January 2008.
A new International Collaboration Agreement for the SKA Program was drawn up in 2007, which became effective on 1 January 2008. It was signed by the European, US, and Canadian SKA Consortia, the Australian SKA Coordination Committee, the National Research Foundation in South Africa, the National Astronomical Observatories in China, and the National Center for Radio Astrophysics in India. This agreement established the SKA Science and Engineering Committee (SSEC) as a replacement to the ISSC. The SSEC acts as the primary forum for interactions and decisions on scientific and technical matters for the SKA among the signatories to the International Collaboration Agreement.
A further agreement was drawn up in 2007, a Memorandum of Agreement to establish the SKA Program Development Office (SPDO). This provided a framework to internationalize the technology development and design effort of the SKA. This agreement, which became effective on 1 January 2008, was signed by the CSIRO Australia Telescope National Facility, University of Calgary, Cornell University, the Joint Institute for VLBI in Europe, and the National Research Foundation in South Africa. It agreed that the SPDO would be funded by signatories of this agreement, with payments being made into the SPDO Common Fund and used to finance the SPDO's operational activities.
The project is now led by the SKA Organization, a not-for-profit company. The organization was established in December 2011 to formalize relationships between the international partners and centralize the leadership of the project.
The Office of the SKA Organization is growing rapidly and in November 2012 the office, previously based at the University of Manchester in the center of the city, relocated to a new building at the world famous Jodrell Bank Observatory in Cheshire, UK. The SKAO Headquarters is the central control hub for a global team who over the next decade is building the SKA – The largest radio telescope ever seen on Earth.
• Participating Countries: Organizations from eleven countries are currently members of the SKA Organisation – Australia, Canada, China, India, Italy, New Zealand, South Africa, Spain, Sweden, the Netherlands and the United Kingdom. Further countries have expressed their interest in joining the SKA Organisation which will continue to expand over the coming years. 3)
Figure 1: While 11 member countries are the core of the SKA, around 100 organisations across about 20 countries (including France, Germany, Japan, Portugal) have been participating in the design and development of the SKA and are now engaged in the detailed design of the telescope (image crdit: SKA)
Here is a list of links to the key participating nations:
- Australia: Department of Industry and Science
- Canada: National Research Council
- Italy: National Institute for Astrophysics
- New Zealand: Ministry of Economic Development
- South Africa: National Research Foundation
- Sweden: Onsala Space Observatory
- The Netherlands: Netherlands Organisation for Scientific Research
- United Kingdom: Science and Technology Facilities Council
• During 2013, the SKA Organization sent out requests to research organizations and commercial partners to participate in the analysis and design of the components of the SKA's 3-year final detailed design phase. This request for proposals included a reference conceptual design of the telescope, a work breakdown structure, a statement of the work required and additional reference documents. 4)
- As with other projects of this magnitude, such as the development of the Large Hadron Collider or space programs, the SKA is broken down into various elements, known as work packages that will form the final SKA telescope. Each work package element is managed by an international consortium comprising several world leading experts in their respective fields.
- The strategic aim of the SKA Organisation is that the work undertaken within each of the consortia is focused on these specific elements of the SKA project and that their work will cover the entire final phase of the pre-construction period, with critical design reviews along the way.
- The SKA Organisation will play a key role in the management of these teams around the world, ensuring that all of the elements integrate to form this unique telescope over the coming years. Each consortium has provided detailed management and verification plans, schedules, milestones and budgets for the various elements they will be working on.
- The consortia responsible for each work package are listed as follows. Click on each to get more detailed information on each work package and the team responsible for its delivery.
c) Dish (DSH)
Collaboration between the various teams will be a key part of their involvement, as there will be a huge requirement to ensure that the various elements interface seamlessly together, much like a jigsaw, but one that will be refined and iterate to a better solution as time progresses.
Technical descriptions for the Work Packages at a global level
Summaries of Technical Descriptions for each of the Work Packages are as follows: (PDF links)
• January 23, 2017: SKA-AAMID (Aperture Array MID Frequency) telescope. 5)
The Location of the SKA
In 2012 the members of the SKA Organization agreed on a dual site location for the Square Kilometer Array telescope as well as a third site for the SKA HQ. 6)
The two sites which will host the core of the SKA Telescope are Australia and South Africa, whilst the SKA Organization Headquarters is in the UK.
This decision to collocate the telescopes in two sites came after careful consideration of all of the science goals, industry goals and suitability in terms of location, sustainability, local considerations and factors relating to economics and the site infrastructure.
The following are some of the criteria that were taken into account:
• Radio frequency interference from mobile phones, TVs, radios and other electrical devices.
• The characteristics of the ionosphere (the upper part of the Earth's atmosphere) and the troposphere (the lower part of the Earth's atmosphere).
• Physical characteristics of the site including climate and subsurface temperatures.
• Connectivity across the vast extent of the telescope itself as well as to communications networks for worldwide distribution of data produced by the SKA.
• Infrastructure costs, including power supply and distribution.
• Operations and maintenance costs.
• The long term sustainability of the site as a radio quiet zone.
In July 2013, the SKA Board passed the following resolution: ‘Following the recommendation of the Director-General of the SKA Organization, the SKA Board has instructed the SKA Office to proceed with the design phase for SKA Phase 1 (SKA1) assuming a capital expenditure cost ceiling for construction of €650 M. The evolution of the SKA Phase 1 project to fit within this cost ceiling will be guided both during the design phase and construction by scientific and engineering assessments of the baseline design undertaken by the SKA Office in collaboration with the community and SKA's advisory bodies including the Science and Engineering Advisory Committee (SEAC). This decision is consistent with the primary objective of building an exciting, next-generation telescope capable of transformational science.'
Table 1: SKA1 baseline design: boundary conditions, design timeline, MID baseline sciene, MID baseline design 7)
Figure 2: SKA1 construction start 2018 (image credit: SKA Office)
Figure 3: SKA2 construction start 2022 (image credit: SKA Office)
Figure 4: SKA overall timeline (image credit: SKA Office)
Australia Antenna Array
Under the joint hosting arrangements, Australia will host the SKA's low frequency aperture array antennas. 8)
In Phase 1, Australia will host over one hundred thousand antennas (each about 2 meters in height) covering low frequency radio waves, to be expanded to up to a million antennas in Phase 2. This array will conduct research into one of the most interesting periods of the Universe, looking back to the first billion years of the Universe to look at the formation of the first stars and galaxies, providing valuable insight into dark matter and dark energy and the evolution of the Universe.
It will provide an increased capability over existing infrastructure at the same frequencies, providing 25% better resolution and being 8 times more sensitive than LOFAR ( Low-Frequency Array) radio telescope, the current best such instrument. Moreover, it will be able to scan the sky 135 times faster. The sheer amount of raw data produced by all these antennas will be equivalent to five times the internet traffic.
ASKAP (Australian Square Kilometer Array Pathfinder) is CSIRO's (Commonwealth Scientific and Industrial Research Organisation) radio telescope currently being commissioned at the Murchison Radio-astronomy Observatory (MRO) in Western Australia. Another important precursor for the SKA located in that region is the MWA (Murchison Widefield Array) 9) 10)
The MRO location is in a remote outback region about 350 km northeast from Geraldton in Western Australia. This follows the signing of an Indigenous Land Use Agreement (ILUA) with the Wajarri Yamatji Claimant Group. This region is ideal for a new radio observatory because the population density is very low and there is a lack of man-made radio signals that would otherwise interfere with weak astronomical signals.
Construction of ASKAP began in early 2010, and all 36 antennas, as well as site infrastructure, were completed in mid-2012. ASKAP is currently undergoing the fit-out of its complex PAF receiver systems and electronics, as well as commissioning.
Figure 5: The core of the Australian SKA activity is located at CSIRO's Murchison Radio-astronomy Observatory (MRO), and surrounding Mid West Radio-Quiet Zone in Western Australia. The MRO is already home to the ASKAP telescope, as well as another of the SKA precursors, the Murchison Widefield Array (MWA), image credit: ATNF
As part of SKA pre-construction, CSIRO is taking a lead role in a number of R&D consortia involved in the design and validation process of the SKA, including ‘Dish', ‘Infrastructure-Australia' and ‘Assembly, Integration and Verification'. The CSIRO SKA Center has also been established to coordinate and guide SKA activities within the organization.
Australia's existing 36 dish ASKAP telescope , each 12 m in diameter, is conducting groundbreaking research into new promising technologies for the SKA. Equipped with PAF (Phased Array Feed) technology, it will be able to survey large areas of the sky in great detail. The PAF for ASKAP provides the antenna with a wide FOV (Field of View) by creating 30 separate (simultaneous) beams to give a FOV of 30 º x 30º (the width of your little finger at arms length is around 1º), speeding up survey time quite considerably. 11)
ASKAP's rapid survey capability makes it one of the world's fastest survey radio telescopes. The PAF receivers have been specifically developed for ASKAP by CSIRO and this is the first time this type of technology has been used in radio astronomy. Traditional radio telescopes are good at providing a detailed view of a distant object. However, what astronomers often want is to study large volumes of space at once. With a traditional radio telescope, we can only do this by painstakingly looking in lots of different directions at different times. ASKAP can image (in 3D) large areas all at once, with much greater sensitivity than previous all-sky surveys. ASKAP has also been designed to be extremely fast - it will be able to detect millions of radio sources in a matter of days, opening new fields of research.
In addition to being a world-leading telescope in its own right, ASKAP is an important technology demonstrator for the SKA. ASKAP's home, the Murchison Radio-astronomy Observatory site will be the central site for major components of SKA telescope infrastructure in Australia.
Figure 6: ASKAP's ‘field of view' is depicted showing the 36 beams as individual circles. We get all of this in one go. By comparison, the field of view of a traditional telescope would be a single slightly smaller circle. The moon diameter is half the diameter of one of these circles (image credit:ATNF)
• Total collecting area of 4,000 m2, from 36 antennas, each 12 m in diameter
• System temperature less than 50 K
• Frequency range from 700 MHz to 1.8 GHz
• 300 MHz instantaneous bandwidth
• 36 independent beams, each of about 1º x 1º, yield overlapping to a 30º x 30º field-of-view at 1.4 GHz
• 6 km maximum baseline
• Full cross-correlation of all antennas
• Remote array station capability located in NSW, approximately 3,000 km from the core site.
Figure 7: Antennas of CSIRO's Australian SKA Pathfinder at the Murchison Radioastronomy Observatory in Western Australia (image credit: CSIRO, Steve Barker)
Figure 8: A phased array feed (PAF) receiver installed on an ASKAP antenna at the Murchison Radioastronomy Observatory (image credit: CSIRO, Barry Turner)
LFAA (Low Frequency Aperture Array)
The LFAA Element, a work package executed by the AADC (Aperture Array Design & Construction) Consortium, is one of the elements of the SKA1-LOW telescope and is defined as the antenna array stations, including the station signal processing, control and calibration. The work is set out in the Statement of Work agreed with the SKAO. 12)
The AADC Consortium team started working together in 2010 with a specific focus on SKA-LOW. Longer connections go back to SKADS, an EU FP6 project which started in 2005. The formation of the Consortium was therefore based on previous work and groups, which made it possible to move quickly to the actual realization and testing of prototypes. In particular Aperture Array Verification System 0.5 (AAVS0.5), was installed at the Murchison Radio Observatory as early as May 2013. This system has proven to be very valuable already (The initial LFAA specification sought to define an array capable of operating from 70-450 MHz).
The three SKA low-frequency pathfinders and precursor telescopes, LOFAR, NenuFAR and MWA, have been designed and realized and are currently operated by members of the AADC Consortium. The experience and knowledge gained is directly available for LFAA. Furthermore both LOFAR and MWA can be used as a test bed for new LFAA technology, this has already been proven to be very effective, most notably in the case of AAVS0.5 and MWA.
November 1st, 2013 marks the start of Stage 1 of the SKA1 preconstruction phase, to be finished in March 2015. The Preliminary Design Review (PDR) is a crucial milestone at the completion of Stage 1. As well as the design documents for PDR, intermediate deliverables have been generated and accepted. By the end of January, the AADC Consortium successfully passed its PDR!
In March 2015 the SKA members decided that SKA1-Low in Australia should be built. 50% of the planned 262,144 low frequency dipoles should be deployed. The array should cover the frequency range 50-350 MHz, as planned. The current planned baseline lengths of ~80km should be retained. The inclusion of a pulsar search capability for SKA1-Low (currently an Engineering Change Proposal on hold) should be actively explored.
The LFAA will be located in Australia, primarily in Western Australia. Observing frequencies in the 50- 350 MHz region, SKA-low will probe 13 billion years back in time to the period when the first stars and galaxies began to form. Phase 1 of SKA-low will deploy roughly 250,000 identical antennas and amplifiers. The array will be supported by local processing technology to combine the individual signals and transport them to the final supercomputing facility that will conduct final data processing and storage. 13)
The antennas have been designed to minimize cost and maximize ease of deployment and reliability in the remote environment. The core of the array will be tightly packed, with 75% of antennas located within a 2 km radius (at approximately 1.5m separation). The remaining antennas will form spiral arms spanning about 50 km to enhance final image detail.
Figure 9: An artist impression of the low frequency antennas in Australia with the ASKAP telescope in the background (image credit: CSIRO)
ASKAP development and mission status
• October 30, 2018: Astronomers from ANU (Australian National University), Canberra, and CSIRO (Commonwealth Scientific and Industrial Research Organization) have witnessed, in the finest detail ever, the slow death of a neighboring dwarf galaxy, which is gradually losing its power to form stars. 14)
- The new peer15)-reviewed study of the Small Magellanic Cloud (SMC), which is a tiny fraction of the size and mass of the Milky Way galaxy, uses images taken with CSIRO's powerful Australian SKA Pathfinder (ASKAP) radio telescope. 16)
- Lead researcher Professor Naomi McClure-Griffiths from ANU said the features of the radio images were more than three times finer than previous SMC images, which allowed the team to probe the interactions between the small galaxy and its environment with more accuracy. "We were able to observe a powerful outflow of hydrogen gas from the Small Magellanic Cloud," said McClure-Griffiths. "The implication is the galaxy may eventually stop being able to form new stars if it loses all of its gas. Galaxies that stop forming stars gradually fade away into oblivion. It's sort of a slow death for a galaxy if it loses all of its gas."
- The discovery, which is part of a project that investigates the evolution of galaxies, provided the first clear observational measurement of the amount of mass lost from a dwarf galaxy. "The result is also important because it provides a possible source of gas for the enormous Magellanic Stream that encircles the Milky Way. Ultimately, the Small Magellanic Cloud is likely to eventually be gobbled up by our Milky Way," according to Naomi McClure-Griffiths.
- CSIRO co-researcher Dr David McConnell said "ASKAP is unrivalled in the world for this kind of research due to its unique radio receivers that give it a panoramic view of the sky. The telescope covered the entire SMC galaxy in a single shot and photographed its hydrogen gas with unprecedented detail.
- Hydrogen is the most abundant element in the Universe, and is the main ingredient of stars.
- "ASKAP will go on to make state-of-the-art pictures of hydrogen gas in our own Milky Way and the Magellanic Clouds, providing a full understanding of how this dwarf system is merging with our own galaxy and what this teaches us about the evolution of other galaxies," Dr McConnell said.
- ASKAP's extremely large field of view is what makes it a uniquely powerful survey instrument. The telescope uses new technology developed by CSIRO - a kind of "radio camera", known as a phased array feed (PAF) that sits at the focus of each of its antennas. We are currently commissioning the telescope and running Early Science observations using up to 16 of ASKAP's 36 antennas. To demonstrate ASKAP's emerging capability as more antennas come on-line, the GASKAP Survey Science Team recently produced this image of the Small Magellanic Cloud. It shows us the tangled web of gas that makes up our neighbouring galaxy and it reveals the galaxy's vibrant history, including streams of gas reeled in by the gravitational pull of the Milky Way and billowing voids generated by massive stars that exploded millions of years ago.
- The new image shows that the Small Magellanic Cloud has had "a very dynamic past", according to Professor McClure-Griffiths from the ANU (Australian National University, Canberra, Australia) Research School of Astronomy and Astrophysics, who jointly led the work with Professor John Dickey of the University of Tasmania.
- What's amazing about this image is that it was made in one shot with the ‘wide-angle' camera of ASKAP. To do this with traditional technology we had to point the telescope in 1,344 different places across the face of the Galaxy and that project required five observing runs over 15 months. By contrast, to make the new image, ASKAP took just three nights . Data from CSIRO's Parkes radio-telescope was added to pick up the faint diffuse emission which is essential for understanding the Galaxy as a whole.
- This new image of Figure 10 is a demonstration of how astronomers will be able to use ASKAP's new technology to map the Universe and improve our understanding of how the Universe works.
- The Small Magellanic Cloud, a dwarf galaxy that is a satellite of our Milky Way Galaxy, is located about 210,000 light-years away in the southern constellation of Tucana. It has a complex structure due to gravitational interaction with the Milky Way and the Large Magellanic Cloud. The new radio image of the Small Magellanic Cloud was created as part of a survey that aims to study the evolution of galaxies.
- According to Professor McClure-Griffiths and colleagues, the new image finally reaches the same level of detail as infrared images from NASA's Spitzer Space Telescope and ESA's Herschel telescope, but on a very different component of the galaxy's make-up — its hydrogen gas.
- "Hydrogen is the fundamental building block of all galaxies and shows off the more extended structure of a galaxy than its stars and dust," Professor McClure-Griffiths said.
Figure 10: Atomic hydrogen gas in the Small Magellanic Cloud as imaged with CSIRO's ASKAP at MRO in 2017 (image credit: ANU and CSIRO)
• June 2018: The culmination of the early science program on ASKAP Array Release 2 is a large-area survey dubbed the cosmology survey, as it is intended to test the idea that key parameters of our cosmological models (our understanding of how the universe formed and expanded to the state we find it in today) can be improved by studying the statistical properties of large numbers of galaxies. 19)
- This survey uses 16 antennas and covers roughly 2000 square degrees, divided into 68 tiled locations that we observe for 200 minutes each. We used a center frequency of 912 MHz and 240 MHz of bandwidth to make the following image from a single beam (roughly 1/36th of ASKAP's full field of view) of one of the first observed regions, showing hundreds of galaxies and several sources with interesting extended structure.
Figure 11: The ASKAP continuum science working group have been using this small area of the survey to tune the ASKAP imaging pipeline parameters in order to optimize the quality of the image before processing the rest of the data and completing the remaining observations.
• May 24, 2018: A complete prototype station of antennas for the future SKA-low telescope has been completed and is being tested at the SKA site in Western Australia. 20)
- In an important engineering milestone, a full station of 256 low-frequency antennas has been deployed and is undergoing tests at CSIRO's Murchison Radio-astronomy Observatory (MRO) in outback Western Australia.
- The demonstrator, known as the AAVS1 (Aperture Array Verification System 1) is being used to help test and finalise the design of the low frequency antennas for the SKA (Square Kilometer Array), known as SKA-low.
- It was installed by an international team from Australia, Italy, Malta, the Netherlands and the United Kingdom over many months, sometimes in harsh conditions.
- "This is a significant achievement by the team, they have done a fantastic job. We have been thinking, discussing and designing together for several years. Putting together and testing this verification system has been an amazing experience." said AAVS1 Project Manager Pieter Benthem. Benthem is based at the Netherlands Institute for Radio Astronomy (ASTRON), the institute that leads the consortium working on the design of the SKA-low telescope.
- The consortium focusing on SKA-low is now working towards its critical design review later this year.
Figure 12: A full station of 256 antennas at CSIRO's Murchison Radio-astronomy Observatory in outback Western Australia. The demonstrator is used to help test and finalize the design of the low frequency antennas for the SKA (image credit: ICRAR/Curtin University)
- "There's still a lot of work to be done, but the lessons we've learnt from AAVS1 will be fed into the larger design process for SKA-low" said ICRAR (International Center for Radio Astronomy Research) Associate Professor Randall Wayth.
- "The antennas used for AAVS1 are what we call second generation prototypes. The tests now being conducted on them are helping predict how the fourth generation will behave. It's all about making sure we get the best possible hardware on site at the end" explains Phil Gibbs, SKA Organisation's Project Manager for the consortium. - "The next steps will be to complete the tests, interpret the results so they can feed into the proposed design for the SKA low telescope and prepare for the critical design review, which is anticipated to take place later this year" he added.
- AAVS1 is in the process of being connected to the Murchison Widefield Array (MWA), one of the four SKA precursor telescopes, which has been operational since 2013. By combining the data of the demonstrator with the MWA, the engineers will be able to fully characterise its on-sky performance.
- Both AAVS1 and MWA have been heavily supported by scientists, engineers and data-intensive astronomy specialists from ICRAR in Perth, Western Australia.
- About the LFAA consortium: The LFAA (Low-Frequency Aperture Array) element is the set of antennas, on-board amplifiers and local processing required for the Aperture Array telescope of the SKA.
- The LFAA consortium is led by the Netherlands Institute for Radio Astronomy (ASTRON) and includes the International Centre for Radio Astronomy Research (ICRAR), Australia; the Key Lab of Aperture Array and Space Application (KLAASA), China; the National Institute for Astrophysics (INAF), Italy; the University of Malta; the Joint Institute for VLBI in Europe (JIVE), the Netherlands; the University of Cambridge, UK; the University of Manchester, UK; the University of Oxford, UK; the Science and Technology Facilities Council (STFC), UK; Observatoire de la Côte d'Azur, France; and Station de Radioastronomie de Nançay, France.
• February 2018: Position offset solution confirmed: The ASKAP project has now confirmation that images made after last year's changes to the delay tracking system are consistent with existing source catalogs (Figure 13). This gives us much more confidence in the system as we continue to develop the fringe rotation module. 21)
- Fringe rotator system commissioning: One of the primary goals right now is the completion and integration of our final fringe tracking system. This should remove a major performance bottleneck in the ingest pipeline and reduce the number of visibilities that need to be flagged.
- Testing of the new CALC-based delay prediction system is well underway on a partial hardware platform in the Marsfield workshop. Low-level tests of the accuracy of the delay tracking firmware have been completed, revealing some problems in the existing software interface that are being addressed before the commencement of tests on the full system using astronomical sources.
- Two major workshop sessions across several engineering teams were held to discuss the timing of the fringe rotator parameter uploads in detail. It is important to ensure that these occur on correlator cycle boundaries to avoid the need for flagging. This discussion also identified a possible improvement in the way that timed events are distributed throughout the digital system. This might reduce the amount of low-level jitter and help improve the dynamic range of the system in the long term.
- Storm monitoring at the MRO: Since ASKAP is expected to be a remotely-operated instrument system, it is important to ensure that its control system has good situational awareness – particularly with respect to severe thunderstorms which can develop rapidly.
- While we have had wind speed monitoring for some time, the MRO covers a large area, where individual anemometer measurements do not provide adequate surveillance. Passing severe weather can trigger microbursts and strong wind gusts that develop more quickly than the antennas can be stowed. Anemometers alone are therefore not good enough to ensure the safety of the telescope.
- CSIRO staff member Balthasar Indermühle recently developed a severe weather protection system based on quasi-realtime satellite data capable of detecting severe convective cells and using other meteorological metrics to accurately predict and observe the approach of potentially harmful conditions. This will help to ensure the safety of both hardware and personnel.
Figure 13: Plot of source position offsets with respect to NVSS (NRAO/VLA Sky Survey) from a recent ASKAP image after delay tracking improvements (image credit: ATNF, CSIRO)
• September 18, 2017: EMU (Evolutionary May of the Universe): EMU is a large project which will use the new ASKAP telescope to make a census of radio sources in the sky. We currently know of about 2.5 million radio sources, and EMU will detect about 70 million. Most of these radio sources will be galaxies millions of light years away, many containing massive black holes, and some of the signals we detect will have been sent less than half a billion years after the Big Bang, which created the Universe 13.7 billion years ago. The reason for doing this is to try to understand how the stars and galaxies were first formed, and how they evolved to their present state, where planets and people are formed. The idea of doing this census is so that we can catch galaxies in all their different stages of evolution, and try to place them in sequence, and so study how their properties change as they evolve. 22) 23)
- All radio data from the survey will be placed in the public domain as soon the data quality has been checked. An integral part of the proposed project will be to perform identifications with other wavelengths, and produce catalogs of these and other "added-value" data products.
- EMU is a radio sky survey project which will use the new ASKAP telescope to make a deep (10 µJy rms) radio continuum survey covering the entire Southern Sky as far North as 30°. It can be characterized as a "Southern NVSS", except that it will have about 40 times the sensitivity, six times the resolution and will detect 70 million galaxies. As a result, it will be able to probe star forming galaxies up to z=1, AGNs to the edge of the Universe, and will undoubtedly uncover new classes of object. 24)
• May 23, 2017: A CSIRO telescope in Western Australia has found its first 'fast radio burst' from space after less than four days of searching. The discovery came so quickly that the telescope, the ASKAP (Australian Square Kilometer Array Pathfinder) near Geraldton in Western Australia, looks set to become a world champion in this fiercely competitive area of astronomy. 25)
- The new fast radio burst finding was published today in the Astrophysical Journal Letters. 26)
- FBRs (Fast Radio Bursts) are short, sharp spikes of radio waves lasting a few milliseconds. They appear to come from powerful events billions of light-years away but their cause is still a mystery. The first was discovered in 2007 and only two dozen have been found since.
- The discovery of the new burst, FRB170107, was made by CSIRO's Keith Bannister and his colleagues from CSIRO, Curtin University and ICRAR (International Center for Radio Astronomy Research ) while using just eight of the telescope's 36 dishes. The discovery is the culmination of a decade of science and engineering development by CSIRO and Curtin University.
- "We can expect to find one every two days when we use 12 dishes, our standard number at present," Dr Bannister said. To make the most recent detection, the researchers used an unusual strategy.
- "We turned the telescope into the Sauron of space – the all-seeing eye," Dr Bannister said, referring to the dark overlord in Tolkien's "Lord of the Rings".
- Usually ASKAP's dishes all point at the one part of sky. But they can be made to point in slightly different directions, like the segments of a fly's eye. This multiplies the amount of sky the telescope can see. Eight ASKAP dishes can see 240º x 240º at once – about a thousand times the area of the full Moon.
- The new burst was found as part of a research project called CRAFT (Commensal Real-time ASKAP Fast Transients survey), which is led jointly by Dr Bannister and Dr Jean-Pierre Macquart from the Curtin University node of ICRAR. Dr Macquart said the new burst was extremely bright and that finding it was "as easy as shooting fish in a barrel".
- FRB170107 came from the edge of the constellation Leo. It appears to have travelled through space for six billion years before slamming into the WA (Western Australian) telescope at the speed of light.
- FRB170107 came from the edge of the constellation Leo. It appears to have travelled through space for six billion years before slamming into the WA telescope at the speed of light. "We've made a hard problem even harder," said Dr Ryan Shannon (CSIRO, Curtin University and ICRAR), who analyzed the burst's strength and position.
- CSIRO Chief Executive Dr Larry Marshall said the FRB detection was a sign of the full potential of ASKAP. "Radio astronomy has a long history of innovation in high-speed communications, and this unique capability is embedded into ASKAP – from the receiver to the signal processing – making it a uniquely powerful instrument for astronomy," Dr Marshall said.
Figure 14: The signal of FRB 170107, found using CSIRO's ASKAP radio telescope in less than four days of looking (image credit: CSIRO (Ref. 26)
Figure 15: The ASKAP telescope pathfinder in Western Australia (image credit: CSIRO)
• January 16, 2017: ASKAP is made of 36 identical 12 m wide dish antennas that all work together, 12 of which are currently in operation. Thirty ASKAP antennas have now been fitted with specialized phased array feeds, the rest will be installed later in 2017. 27)
- Until now, the project had been taking data mainly to test how ASKAP performs. Having shown the telescope's technical excellence it's now off on its big trip, starting to make observations for the big science projects it'll be doing for the next five years.
- And it's taking lots of data. Its antennas are now churning out 5.2 TB/s of data (about 15 per cent of the internet's current data rate).
- Once out of the telescope, the data is going through a new, almost automatic data-processing system we've developed.
- The first project we've been taking data for is one of ASKAP's largest surveys, WALLABY (Widefield ASKAP L-band Legacy All-sky Blind surveY).
- On board the survey are a happy band of 100-plus scientists – affectionately known as the WALLABIES – from many countries, led by one of our astronomers, Bärbel Koribalski, and Lister Staveley-Smith of the International Centre for Radio Astronomy Research (ICRAR), University of Western Australia.
- They're aiming to detect and measure neutral hydrogen gas in galaxies over three-quarters of the sky. To see the farthest of these galaxies they'll be looking three billion years back into the universe's past, with a redshift of 0.26.
Figure 16: Neutral hydrogen gas in one of the galaxies, IC 5201 in the southern constellation of Grus (The Crane), imaged in early observations for the WALLABY project (image credit: CSIRO, Matthew Whiting, Karen Lee-Waddell and Bärbel Koribalski, all of WALLABY)
- Neutral hydrogen – just lonely individual hydrogen atoms floating around – is the basic form of matter in the universe. Galaxies are made up of stars but also dark matter, dust and gas – mostly hydrogen. Some of the hydrogen turns into stars.
- Although the universe has been busy making stars for most of its 13.7-billion-year life, there's still a fair bit of neutral hydrogen around. In the nearby (low-redshift) universe, most of it hangs out in galaxies. So mapping the neutral hydrogen is a useful way to map the galaxies, which isn't always easy to do with just starlight.
- But as well as mapping where the galaxies are, we want to know how they live their lives, get on with their neighbors, grow and change over time.
- When galaxies live together in big groups and clusters they steal gas from each other, a processes called accretion and stripping. Seeing how the hydrogen gas is disturbed or missing tells us what the galaxies have been up to.
- We can also use the hydrogen signal to work out a lot of a galaxy's individual characteristics, such as its distance, how much gas it contains, its total mass, and how much dark matter it contains. This information is often used in combination with characteristics we learn from studying the light of the galaxy's stars.
- ASKAP sees large pieces of sky with a field of view of 30º x 30 º. The WALLABY team will observe 1,200 of these fields. Each field contains about 500 galaxies detectable in neutral hydrogen, giving a total of 600,000 galaxies.
Figure 17: One of the first fields targeted by WALLABY, the NGC 7232 galaxy group. This image of the NGC 7232 galaxy group was made with just two nights' worth of data (image credit: Ian Heywood (CSIRO); WALLABY team)
- ASKAP has now made 150 hours of observations of this field, which has been found to contain 2,300 radio sources (the white dots), almost all of them galaxies.
- It has also observed a second field, one containing the Fornax cluster of galaxies, and started on two more fields over the Christmas and New Year period.
• The ASKAP Early Science Program started in October 2016 using an array of 12 antennas (Ref. 11).
• April 10, 2014: The ASKAP team has this week produced the first BETA spectral line image using six ASKAP antennas installed with innovative PAF (Phased Array Feed) receiver systems, as part of ongoing commissioning tests at the MRO (Murchison Radio-astronomy Observatory) in Western Australia. 28)
- ASKAP is one of two Australian SKA precursor telescopes. It forms part of the Australia Telescope National Facility or ATNF, a collection of radio astronomy observatories operated and managed by CSIRO, Australia's national science agency.
- This milestone is quite significant for the ASKAP project – particularly in terms of the technical implications of demonstrating the success of the design of the system.
Figure 18: With the recently reconfigured hardware correlator and the six-antenna test array known as the Boolardy Engineering Test Array (BETA), an observation was made with up to six hours of data collected and analyzed to create the first spectral line image, and data cube, with the ASKAP system (image credit: ATNF,CSIRO)
- The chosen target was the strong gravitational lens system PKS1830-211, used in previous commissioning tests with the ASKAP system because of the strong HI absorption feature at a redshift of z=0.88, or 753 MHz. This feature also makes the source an ideal target for BETA, which is one of just a few telescopes capable of such an observation at this frequency.
- The resulting image is the first to incorporate all 15 baselines from the BETA system, and also the first to be made with the array's full spectral resolution of 18 kHz. While still quite preliminary, the accompanying spectrum is of particular interest to the team.
- Close comparison with spectra previously taken with the Westerbork radio telescope at a similar resolution has shown a second feature which appears more pronounced in the new BETA spectrum than previously seen, indicating an interesting opportunity for scientific follow up.
Africa Radio Telescope Array
The desert regions of South Africa, provide the perfect radio quiet backdrop for the high and medium frequency arrays that will form a critical part of the SKA's ground-breaking continent wide telescope. 29)
South Africa is not alone in hosting components for the SKA in Africa. Eight partner countries around the African continent will also have radio telescopes contributing to the network that will provide scientists with the world's most advanced radio astronomy array. These include Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia and Zambia.
South Africa is already host to the KAT7 telescope array, an important testing ground for the MeerKAT telescope array, a 64 dish system which will form a precursor to the full SKA Telescope.
In SKA Phase 1, the 64-dish MeerKAT precursor array which is currently under construction and expected to come online in a few years time will be integrated into SKA1 MID (Mid Frequency Antennas), with the construction of another 130 dishes. In total, SKA1 MID will count almost 200 dishes spread around the Karoo.
SKA1 MID will conduct observations in many exciting areas of science, such as gravitational waves, pulsars, and will search for signatures of life in the galaxy. It will provide a jump in capability, providing 4 times more resolution and 5 times more sensitivity than the JVLA (Jansky Very Large Array), the current best telescope as similar frequencies. Additionally, it will be able to map the sky 60 times faster.
Thousands of SKA antenna dishes will be built in South Africa (in the Karoo, not far from the small town called Carnarvon), with outstations in other parts of South Africa, as well as in eight African partner countries, namely Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia and Zambia. Another part of the telescope, the low-frequency array, will be built in Western Australia. 30)
MeerKAT Radio Telescope Array
The South African MeerKAT radio telescope, currently being built some 90 km outside the small Northern Cape town of Carnarvon, is a precursor to the SKA (Square Kilometer Array) telescope and will be integrated into the mid-frequency component of SKA Phase 1. The SKA Project is an international enterprise to build the largest and most sensitive radio telescope in the world, and will be located in Africa and Australia. 31)
Why MeerKAT? -The telescope was originally known as the Karoo Array Telescope (KAT) that would consist of 20 receptors. When the South African government increased the budget to allow the building of 64 receptors, the team renamed it "MeerKAT" – i.e. "more of KAT". The MeerKAT (scientific name Suricata suricatta) is also a much-beloved small mammal that lives in the Karoo region.
Figure 19: In 2016, more than 20 MeerKAT antennas have been installed on the SKA SA Losberg site outside Carnarvon in the Northern Cape (image credit: SKA Africa)
MeerKAT is a precursor to the SKA and follows the KAT-7 telescope which was an engineering test-bed for MeerKAT. MeerKAT is funded by the South African Government and is a South African designed telescope with 75% of its value sourced locally. An important aspect of the SKA site decision in 2012 was that MeerKAT would be part of the sensitive SKA Phase 1 array, which will be the most sensitive radio telescope in the world. Upon completion at the end of 2017, MeerKAT will consist of 64 dishes and associated instrumentation. SKA 1 MID will include an additional 133 dishes, bringing the total number for SKA1 MID to 197.
• The MeerKAT telescope will be an array of 64 interlinked receptors (a receptor is the complete antenna structure, with the main reflector, sub-reflector and all receivers, digitizers and other electronics installed).
• The configuration (placement) of the receptors is determined by the science objectives of the telescope.
• 48 of the receptors are concentrated in the core area which is approximately 1 km in diameter.
• The longest distance between any two receptors (the so-called maximum baseline) is 8 km.
• Each MeerKAT receptor consists of three main components:
1) The antenna positioner, which is a steerable dish on a pedestal
2) A set of radio receivers
3) A set of associated digitizers.
• The antenna positioner is made up of the 13.5 m effective diameter main reflector, and a 3.8 m diameter sub-reflector. In this design, referred to as an ‘Offset Gregorian' optical layout, there are no struts in the way to block or interrupt incoming electromagnetic signals. This ensures excellent optical performance, sensitivity and imaging quality, as well as good rejection of unwanted radio frequency interference from orbiting satellites and terrestrial radio transmitters. It also enables the installation of multiple receiver systems in the primary and secondary focal areas, and provides a number of other operational advantages.
• The combined surface accuracy of the two reflectors is extremely high with a deviation from the ideal shape being no more than 0.6 mm RMS (root mean square). The main reflector surface is made up of 40 aluminum panels mounted on a steel support framework.
• This framework is mounted on top of a yoke, which is in turn mounted on top of a pedestal. The combined height of the pedestal and yoke is just over 8 m. The height of the total structure is 19.5 m with a mass of 42 tons.
• The pedestal houses the antenna's pointing control system.
• Mounted at the top of the pedestal, beneath the yoke, are an azimuth drive and a geared azimuth bearing, which allow the main and sub-reflectors, together with the receiver indexer, to be rotated horizontally. The yoke houses the azimuth wrap, which guides all the cables when the antenna is rotated, and prevents them from becoming entangled or damaged. The structure allows an observation elevation range from 15 to 88 degrees, and an azimuth range from -185 degrees to +275 degrees, where north is at zero degrees.
• The steerable antenna positioner can point the main reflector very accurately, to within 5 arcseconds (1.4 thousandths of a degree) under low-wind and night-time observing conditions, and to within 25 arcseconds (7 thousandths of a degree) during normal operational conditions.
About MeerKAT – how it works:
• Electromagnetic waves from cosmic radio sources bounce off the main reflector, then off the sub-reflector, and are then focused in the feed horn, which is part of the receiver.
• Each receptor can accommodate up to four receivers and digitizers mounted on the receiver indexer. The indexer is a rotating support structure that allows the appropriate receiver to be automatically moved into the antenna focus position, depending on the desired observation frequency.
• The main function of the receiver is to capture the electromagnetic radiation and convert it to an voltage signal that is then amplified by cryogenic receivers that add very little noise to the signal. The first two receivers will be the L-band and UHF-band receivers.
• Four digitizers will be mounted on the receiver indexer, close to the associated receivers. The function of the four digitizers is to convert the RF (Radio Frequency) voltage signal from the receiver into digital signals. This conversion is done by using an electronic component called an ADC (Analog to Digital Converter). The L-band digitizer samples at a rate of 1712 million samples every second. (The amount of data that is generated by the digitizer for a receiver is equivalent to approximately 73,000 DVDs every day or almost 1 DVD/s).
• Once the signal is converted to digital data, the digitizer sends this data via buried fiber optic cables to the correlator, which is situated inside the KAPB (Karoo Array Processor Building) at the Losberg site complex.
• A total of 170 km of buried fiber cables connect the receptors to the KAPB, with the maximum length between the KAPB and a single antenna being 12 km.
• The fiber cables run inside conduits buried 1 m below the ground for thermal stability.
• At the KAPB, the signals undergo various stages of digital processing, such as correlation – which combines all the signals from all the receptors to form an image of the area of the sky to which the antennas are pointing – and beam-forming, which coherently adds the signals from all the receptors to form a number of narrow, high sensitivity beams used for pulsar science. The science data products are also archived at the KAPB with a portion of the science archive data moved off site via fiber connection and stored in Cape Town (with possibilities of reprocessing the data).
• Time and frequency reference signals are distributed, via buried optical fibers, to every digitizer on every receptor, so that they are all synchronized to the same clock. This is important to properly align the signals from all receptors.
• The control and monitoring system is responsible for monitoring the health of the telescope and for controlling it to do what the operators want it to do. A large number of internal sensors (more than 150 000) monitor everything from electronic component temperatures to weather conditions and power consumption.
Table 2: MeerKAT technical specifications
Figure 20: Photo of a MeerKAT antenna: Total height = 19.5 m, total mass of the structure = 42 tons (image credit: SKA Africa)
Some background on MeerKAT:
• The location of the MeerKAT, which will form the core of the bigger SKA telescope, has been carefully chosen to host a radio astronomy instrument for its attractiveness as an excellent radio frequency protected zone and the site continues to attract international collaborations. The Hydrogen Epoch of Reionization Array (HERA) and its predecessor, the Precision Array for Probing the Epoch of Re-ionization (PAPER) are excellent examples. The hosting of these instruments brings numerous economic benefits to the adjacent communities. Since activities of the SKA project started in the Northern Cape, SKA SA has made a number of positive impacts to the lives of the people of Carnarvon, Williston, Van Wyksvlei, Brandvlei, Vosburg, Loxton, Fraserburg and Calvinia. 32)
- The construction of the KAT-7, MeerKAT, the HERA and PAPER has created a total number of 7284 direct and indirect jobs. To date, R136 million has been spent at local suppliers for the construction of the above-mentioned projects.
• The desert regions of South Africa, provide the perfect radio quiet backdrop for the high and medium frequency arrays that will form a critical part of the SKA's ground-breaking continent wide telescope. South Africa is not alone in hosting components for the SKA in Africa. Eight partner countries around the African continent will also have radio telescopes contributing to the network that will provide scientists with the world's most advanced radio astronomy array. These include Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia and Zambia. 33)
- SKA 1 MID (SKA's Mid-frequency instrument) will conduct observations in many exciting areas of science, such as gravitational waves, pulsars, and will search for signatures of life in the galaxy. It will provide a jump in capability, providing 4 times more resolution and 5 times more sensitivity than the JVLA (Jansky Very Large Array) the current best telescope at similar frequencies. Additionally, it will be able to map the sky 60 times faster.
- Mid frequency aperture array antennas are currently under development and could be installed in Africa in Phase 2. The MFAA ("Mid-Frequency Aperture Array) element of the SKA, part of the SKA Advanced Instrumentation Program, includes the activities necessary for the development of a set of antennas, on board amplifiers and local processing required for the Aperture Array telescope of the SKA. MFAA includes the development of local station signal processing and hardware required to combine the antennas and the transport of antenna data to the station processing.
- "The fully sampled field-of-view, of the order of 100 square degrees, makes the SKA Mid-Frequency Aperture Array effectively a 10-gigapixel ultra wide field spectroscopic camera", says Steve Torchinsky, member of the MFAA Consortium and astronomer at the Station de Radioastronomie de Nançay, France.
- The overriding objectives of the MFAA Consortium are to prove the technological maturity of the MFAA technology, and to evaluate different concepts of front-end technology that can serve to assist in the preliminary design of the MFAA. When a concept is selected, it will then be taken further in Stage 2 towards the preliminary design.
Figure 21: Computer generated image of what the SKA Phase 2 dish antennas will look like in South Africa (image credit: SKA Project Office)
MeerKAT development and mission status
• August 17, 2018: The South African Radio Astronomy Observatory (SARAO) celebrates after the SKA Telescope Manager Critical Design Review has been completed. 34)
- SARAO made a significant contribution to the Telescope Manager consortium, which is one of 12 engineering consortia representing 500 engineers in 20 countries building the SKA Observatory and Telescopes. Nine of the consortia focused on a component of the telescope, each critical to the overall success of the project, while three others focused on developing advanced instrumentation for the telescope. The Telescope Manager consortium was itself comprised of nine institutions in seven countries.
- The Telescope Manager consortium was formed in 2013 and was tasked with designing the crucial software that will control and monitor the SKA Observatory and Telescopes, essentially forming its central nervous system. This implies that the Telescope Manager element is connected to all other elements such as the correlator, science processor, dishes and low frequency aperture arrays, and coordinates their actions.
- The Telescope Manager will receive thousands of sensor updates per second, and needs to figure out what actions to take based on this information. The Telescope Manager also provides key stakeholders with user interfaces, for example it will provide operators with a view of the health and status of each telescope.
- The design of the SKA Telescope Manager has recently been subjected to a Critical Design Review (CDR), and has subsequently passed this stage gate, achieving a CDR closure certificate. The review was held in April of this year, was led by the SKA Organization, and included a panel of international experts in the field. The Telescope Manager consortium is the first consortium out of twelve to pass this rigorous review.
- SARAO led the Telescope Manager System Engineering team involved in the design of this vital component, and also participated in the Management work package. SARAO team members acted as the primary authors of a range of important design artefacts, such as requirement and compliance specifications, interface control documents, construction and verification plans to name a few.
- Ray Brederode, Functional Manager for Software at SARAO, and his team comprising Paul Swart, Lize van der Heever and Gerhard le Roux, all from the Software Team at SARAO, participated in the design of the Telescope Manager element.
- "We are proud that the MeerKAT CAM system was selected as the reference design for TM. We also congratulate Professor Yashwant Gupta of GMRT in India, the TM Consortium Chair, for leading the first consortium to successfully achieve CDR," says Dr Rob Adam, Managing Director of SARAO.
- While the Telescope Manager consortium now formally ceases to exist, the SKA Organization continues to work with SARAO and the other former consortium members on the System Design and the SKA construction proposal, where its expertise will be required to ensure that the system design works in conjunction with the other elements.
- The Telescope Consortium members included the South African Radio Astronomy Observatory (SARAO); the Commonwealth Scientific and Industrial Research Council (CSIRO) in Australia; the National Research Council of Canada (NRC), TCS Research and Innovation and Persistent Systems in India; Italy's National Institute for Astrophysics (INAF); Portugal's ENGAGE SKA Consortium through Instituto de Telecomunicações (IT) and the School of Sciences of Porto University; and the UK's Astronomy Technology Centre funded by the Science and Technology Facilities Council (STFC).
Figure 22: Partial view of the 64-antenna MeerKAT radio telescope which will be incorporated into Phase 1 of the SKA-MID telescope (image credit: SARAO)
• July 16, 2018: The recently launched MeerKAT radio telescope in the Northern Cape has paved the way for 72 students to further their studies. Astronomers working at the site outside the town of Carnarvon say besides groundbreaking research, the facility also has other socio-economic spin-offs. 35)
- Besides revolutionary research work, SKA (Square Kilometer Array) South Africa also invests in human capital development programs.
- Officials say a number of schools in the region benefit from these initiatives. Former Carnarvon High School learner, aged 21, Janethan de Klerk now studies computer science at the University of the Free State. "They literally helped us register until the end and it has opened doors for me since my parents couldn't afford it. I had to take this opportunity and make the best out of it."
MeerKAT Inauguration: On 13 July 2018, Deputy President of the Republic of South Africa, Mr David Mabuza, today officially inaugurated the MeerKAT 64-dish radio telescope. After a decade in design and construction, this project of South Africa's Department of Science and Technology has now begun science operations. At the launch event, a panorama obtained with the new telescope was unveiled that reveals extraordinary detail in the region surrounding the supermassive black hole at the center of our Milky Way Galaxy. This is one of several very exciting new views of the Universe already observed by the telescope. 36)
Figure 23: This image, taken by the MeerKAT Radio Telescope, is considered the clearest view of the center of the Milky Way and includes never before seen features and star-forming regions, and radio filaments. At the distance of the galactic center (located within the white area near image center), this 2º x 1º panorama corresponds to an area of approximately 1,000 light-years by 500 light-years. The color scheme chosen here to display the signals represents the brightness of the radio waves recorded by the telescope (ranging from red for faint emission to orange to yellow to white for the brightest areas), image credit: SARAO
- "We wanted to show the science capabilities of this new instrument", says Fernando Camilo, chief scientist of the South African Radio Astronomy Observatory (SARAO), which built and operates MeerKAT in the semi-arid Karoo region of the Northern Cape. "The center of the galaxy was an obvious target: unique, visually striking and full of unexplained phenomena – but also notoriously hard to image using radio telescopes", according to Camilo. The center of the Milky Way, 25,000 light-years away from Earth and lying behind the constellation Sagittarius (the "Teapot"), is forever enshrouded by intervening clouds of gas and dust, making it invisible from Earth using ordinary telescopes. However, infrared, X-ray, and in particular, radio wavelengths penetrate the obscuring dust and open a window into this distinctive region with its unique 4 million solar mass black hole. "Although it's early days with MeerKAT, and a lot remains to be optimized, we decided to go for it – and were stunned by the results."
- "This image is remarkable", says Farhad Yusef-Zadeh of Northwestern University in Evanston, Illinois, one of the world's leading experts on the mysterious filamentary structures present near the central black hole but nowhere else in the Milky Way. These long and narrow magnetized filaments were discovered in the 1980s using the VLA (Very Large Array ) radio telescope in New Mexico, but their origin has remained a mystery. "The MeerKAT image has such clarity", continues Yusef-Zadeh, "it shows so many features never before seen, including compact sources associated with some of the filaments, that it could provide the key to cracking the code and solve this three-decade riddle".
- Yusef-Zadeh adds that "MeerKAT now provides an unsurpassed view of this unique region of our galaxy. It's an exceptional achievement, congratulations to our South African colleagues. They've built an instrument that will be the envy of astronomers everywhere and will be in great demand for years to come".
- MeerKAT, with its 64 antennas, is an SKA precursor telescope and it will ultimately be incorporated into the SKA's mid-frequency array of some 200 dishes in the Karoo region, but it is a world-class facility in its own right and promises to deliver even more exciting science in the coming years. 37)
- "MeerKAT stands at the end of a chapter, and at the start of another one," said SKA Director-General Prof. Phil Diamond in an address at the ceremony. "South Africa and the South African people should be proud: this is a fantastic milestone for the country, that will certainly make history. Now the science can start in earnest, and you can reap the scientific benefits of all your hard work."
- The 64 dishes provide 2,000 unique antenna pairs, far more than any comparable telescope, resulting in high-fidelity images of the radio sky. The image unveiled today shows the clearest view yet of the central regions of our galaxy.
• July 3, 2018: After a decade in the works, South Africa's MeerKAT telescope (Figure 24), a precursor to the SKA (Square Kilometer Array) mid-frequency telescope, is beginning science operations. MeerKAT is a radio interferometer located in the semi-arid and sparsely populated Karoo region of the Northern Cape. The array consists of 64 antennas 13.5 m in diameter located on baselines of up to 8 km. 38)
Figure 24: Part of the 64-dish MeerKAT array (image credit: South African Radio Astronomy Observatory)
- The distribution of the antennas, with three quarters of them located within a 1 km-diameter core, makes MeerKAT particularly suited to a variety of pulsar and neutral hydrogen studies. Several of the selected large survey projects (Lisps), which will use two thirds of the available observing time within five years, will address key questions related to galaxy formation and evolution. For instance, the unique combination of column density sensitivity and angular resolution will make MeerKAT a powerful probe for studying accretion onto galaxies in the nearby Universe. Projects will investigate the range of conditions from star-forming disks to low-density gas in dark matter haloes in isolated galaxies, and will examine how galaxies interact within rich clusters, while seeking to detect the cosmic web. Further afield, the 21 cm line of neutral hydrogen will be used to investigate the properties and evolution of galaxies across two thirds of cosmic time.
• April 2018: New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR-J1622–4950 indicate that the magnetar, in a quiescent state since at least early 2015, reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100 x larger than during its dormant state. The X-ray flux one month after reactivation was at least 800 x larger than during quiescence, and has been decaying exponentially on a 111±19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3–6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6–8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation. 39)
• May 19,2017: The South African SKA precursor telescope MeerKAT has just released its recent AR1.5 (Array Release 1.5) results, images achieved by using various configurations of the 32 antennas currently operational in the Karoo. 40)
- This milestone of the integration of 32 antennas with single polarization correlator was achieved on schedule by the end of March 2017. The 32 antennas are part of the eventual 64 antennas which are being built at the Losberg site in the Northern Cape.
- New radio and X-ray observations of PSR-J1622–4950 that demonstrate that this magnetar most likely reactivated between 2017 March 19 and April 5. This is the first magnetar for which radio emission has been re-detected following a long period of inactivity.
• July 16, 2016: The MeerKAT First Light image of the sky, released today by Minister of Science and Technology, Naledi Pandor, shows unambiguously that MeerKAT is already the best radio telescope of its kind in the Southern Hemisphere. Array Release 1 (AR1) being celebrated today provides 16 of an eventual 64 dishes integrated into a working telescope array. It is the first significant scientific milestone achieved by MeerKAT, the radio telescope under construction in the Karoo that will eventually be integrated into the SKA (Square Kilometer Array). 41)
- In a small patch of sky covering less than 0.01 percent of the entire celestial sphere, the MeerKAT First Light image shows more than 1300 galaxies in the distant Universe, compared to 70 known in this location prior to MeerKAT. "Based on the results being shown today, we are confident that after all 64 dishes are in place, MeerKAT will be the world's leading telescope of its kind until the advent of SKA," according to Professor Justin Jonas, SKA South Africa Chief Technologist.
- MeerKAT will consist of 64 receptors, each comprising a 13.5 m diameter dish antenna, cryogenic coolers, receivers, digitizer, and other electronics. The commissioning of MeerKAT is done in phases to allow for verification of the system, early resolution of any technical issues, and initial science exploitation. Early science can be done with parts of the array as they are commissioned, even as construction continues. AR1 consists of 16 receptors, AR2 of 32 and AR3 of 64, expected to be in place by late 2017.
- In May 2016, more than 150 researchers and students, two-thirds from South Africa, met in Stellenbosch to discuss and update the MeerKAT science program. This will consist of already approved "large survey projects", plus "open time" available for new projects. An engineering test image, produced with only 4 dishes, was made available just before that meeting.
- "The scientists gathered at the May meeting were impressed to see what 4 MeerKAT dishes could do," says Dr Fernando Camilo, SKA South Africa Chief Scientist. "They will be astonished at today's exceptionally beautiful images, which demonstrate that MeerKAT has joined the big leagues of world radio astronomy".
Figure 25: MeerKAT First Light image. Each white dot represents the intensity of radio waves recorded with 16 dishes of the MeerKAT telescope in the Karoo (when completed, MeerKAT will consist of 64 dishes and associated systems). More than 1300 individual objects – galaxies in the distant universe – are seen in this image (image credit: SKA Africa)
Figure 26: View showing 10% of the full MeerKAT First Light radio image. More than 200 astronomical radio sources (white dots) are visible in this image, where prior to MeerKAT only five were known (indicated by violet circles). This image spans about the area of the Earth's moon (image credit: SKA Africa)
• March 31,2014: General Dynamics SATCOM Technologies, a part of General Dynamics Mission Systems, and Stratosat Datacom (Pty) Ltd., a South African company and the prime contractor for this project, have installed the first of the 64 MeerKAT radio telescope antennas to form the MeerKAT array. The array, located in South Africa's Karoo region, is a technologically advanced radio telescope designed to detect and map radio-frequency signals coming from the furthest reaches of the universe. 42)
- The MeerKAT array will be the largest and most sensitive radio telescope in the southern hemisphere and represents the first significant installation of the SKA (Square Kilometer Array) that is scheduled for completion in 2024.
Figure 27: On March 27th 2014, the first General Dynamics-built antenna for the MeerKAT radio telescope was launched in South Africa. When completed, the MeerKAT array will be the largest and most sensitive radio telescope in the southern hemisphere (image credit: SKA South Africa)
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).