South Africa’s first radio telescope array, the seven- dish KAT-7 located in the Karoo, which was originally intended to be a prototype for the much larger MeerKAT array, has now established itself as an effective scientific instrument. The first scientific paper produced from research using KAT-7 was released online on May 16 by the UK journal Monthly Notices of the Royal Astronomical Society (which is one of the oldest and most prestigious scientific journals in the world, and has been in continual publication for some 186 years).
“KAT-7 was really intended as an engineering test-bed to refine the design and systems for the MeerKAT telescope that we are working on now, but we are absolutely delighted that it has turned out to be a top-quality science instrument, capable of producing significant science,” affirmed Square Kilometre Array (SKA) South Africa associate director: science and engineering Professor Justin Jonas. “We plan to continue using KAT-7 to do science until at least 2015, when part of the 64-dish MeerKAT telescope will become available to researchers.”
A team of local and overseas astronomers used KAT-7 in paral- lel with the 26 m dish at the Hartebeesthoek Radio Astronomy Observatory (HartRAO), west of Pretoria, to observe the Circinus X-1 binary star system. The two instruments observed Circinus X-1 at the same time but at different frequencies. The team then analysed the data they had gathered.
This binary star system is composed of a star similar to our sun and a neutron star (which is the extremely compact – about 20 km in diameter – but incredibly dense remnant of a massive star that exploded into a supernova). They orbit each other in an elliptical orbit every 16.5 days. When they are closest together, the neutron star drags material off its companion. This material forms an accretion disc around the neutron star. Some of this material subsequently hits the surface of the neutron star, producing X-rays and, as a result, Circinus X-1 is classified as an X-ray binary. In fact, it is one of the most luminous X-ray binaries known.
In sharp contrast, other material is accelerated away from the neutron star at close to the speed of light in two very powerful, compact and long jets (one from each pole). These jets, in turn, trigger powerful radio wavelength flares when they collide with gas clouds surrounding the binary system. It was these flares for which the KAT-7 and HartRAO instruments were used to study.
“These types of observations help us to understand how matter is accreted onto extremely dense systems, such as neutron stars and black holes,” explained University of Cape Town SKA fellow Dr Richard Armstrong. “They also shed light on how neutron stars are able to generate these powerful outflows and associated radio bursts.” KAT-7 caught two of these flares during its observations of Circinus X-1 and recorded their development. It was the first time this system had been subjected to detailed observation during more than one flare cycle.
“This is a significant milestone for South Africa’s SKA project, proving our engineers are able to deliver a cutting-edge scientific instrument, and that our scientists are able to use it for frontier science,” enthused Science and Technology Minister Derek Hanekom. “It bodes well for the delivery of our 64-dish MeerKAT telescope, currently under construction in the Karoo, and for our ability to play a key role in building and commissioning thousands of SKA antennas over the next ten years.”