MeerKAT precursor achieves major milestones

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MeerKAT, the world-class radio telescope being built by the Department of Science and Technology (DST) and the National Research Foundation (NRF) in the Karoo near Carnarvon, has achieved a major milestone. The MeerKAT Precursor Array (MPA – also known as KAT-7) has produced its first interferometric image of an astronomical object when four of the seven dishes were linked together as an integrated system.

The first combined signals (or “fringes”) were obtained from a range of celestial radio sources in December using the first two fully equipped antennas. The first Raster scan image was produced in March by scanning individual antennas across the Centaurus A radio galaxy. This provided a very successful end-to-end demonstration of antenna hardware, system stability, pointing accuracy and software, the Square Kilometre Array (SKA) South African Project (SKA-SAP) that runs MeerKAT said in a statement today.

Once the antennas were demonstrated to work well individually, another major milestone was achieved last month: phase closure (using three antennas) and amplitude closure (using four antennas), which demonstrated that the underlying system was working as expected and the antennas could be linked together.

The latest development was linking four 12-meter diameter antennas as they observed the Centaurus A galaxy. “The signals collected by the radio antennas were processed by state-of-the-art electronics and control software to transform the four antennas into a single, high-resolution telescope system, called an interferometer. The data were recorded to a computer disk and processed with advanced software to produce an image of a jet being ejected from the black hole the core of this amazing galaxy,” the statement added. (See Picture 2)

The SKA-SAP says Centaurus A is a peculiar galaxy shrouded by a lane of gas and dust, created when a larger elliptical galaxy began to collide with a smaller spiral galaxy. This colliding galaxy is located about 14 million light-years away from earth in the constellation of Centaurus. “Although it takes 14 million years for the light from Centaurus A to reach us, it is still one of the closest radio galaxies to earth. Radio galaxies are galaxies that emit large amounts of radio energy that is invisible to the naked eye and optical telescopes.”

Previous observations of Centaurus A by other radio telescopes and X ray telescopes have shown that a super-massive black hole at the center of the galaxy ejects a stream of high energy particles in a jet that is moving at about one half the speed of light (about 150 000 000 meters per second). As this jet flows into inter-galactic space, ultra-relativistic, charged particles in the million-degree gas move through magnetic fields producing radio emission (this process is called “synchrotron emission”).

The spectacular Centaurus A galaxy is the fifth brightest in the sky and is well studied by amateur and professional astronomers alike. The galaxy is beautifully located high in the southern hemisphere sky near the well-known constellation of the Southern Cross. Because it is so well-studied and it is bright at radio wavelengths, Centaurus A is an ideal celestial object to verify that the complicated electronics and control software in the MPA are working as expected and they produce images with structure that is consistent with what other telescopes have detected,” the SKA-SAP says. This commissioning phase of the project is a vital test to prove that the underlying hardware and software, created by the expert team in South Africa and their industry partners, are ready for the next phase of construction.

The statement adds the interferometric image of Centaurus A was produced from a 6-hour observation using non-cryogenically cooled, test receivers. “Although the receivers were not cooled, the central core of the Centaurus A galaxy has been easily detected. The image was produced by the MeerKAT engineering team based in Cape Town and used software they developed for the purpose of initial exploration and commissioning of the MeerKAT Precursor. No editing of the data was performed in the production of the first image, which shows the excellent radio quietness characteristics of the South African site. The data have been roughly calibrated and the final image has a signal-to-noise level of about 20. The image resolution is about 7’x4′ with a position angle of about 6deg.”

The image produced compares very favourably with what is expected. “We are extremely pleased by the rapid progress and early results obtained from the first MPA antennas”, says SKA-SAP director Dr Bernie Fanaroff. “This shows that we are well on track with the development of our SKA site, and the development of the systems and understanding required to build and operate advanced scientific instruments such as MeerKAT and the SKA. It also shows that our team is as good as any in the world today and we are very proud of them.”

He adds the initial image of Centaurus A, “although an important milestone, is a first demonstration only. A better image of this galaxy and other celestial sources will be possible once all seven antennas in the MPA are brought together to form a fully-functional radio telescope array. … the more well distributed antennas in an array, the better the quality of the image. That is why it is so important to build the MeerKAT array, with 80 antennas planned for construction. MeerKAT with its larger number of dishes and carefully optimized layout will make it possible to construct much higher quality radio images.”

MeerKAT is scheduled to be completed by December 2012 and commissioned in 2013. It is set to cost R860 million and forms part of the R1.6 billion budget Cabinet last year approved for the country to win the right to host the 3000 to 5000-dish 1.5 billion euro (R160 billion) Square Kilometre Array (SKA).

Pic 1: Three of the seven MPA dishes. The nearer one was used to detect the Raster image.

Pic 2: The Raster image, left, with the new inferometric image top right. A NASA optical image of the same area shown right below. Source: SKA