16 May 2013
In a significant milestone for South Africa’s Square Kilometre Array (SKA) project, the first scientific paper based on observations using the KAT-7 demonstrator radio telescope has been accepted for publication by the prestigious journal Monthly Notices of the Royal Astronomy Society.
The seven-dish KAT-7 is paving the way for the 64-dish MeerKAT telescope, due to be commissioned in 2014/15 both as a precursor to the SKA and as one of the most powerful telescopes in the world in its own right.
“This is a significant milestone for South Africa’s SKA project, proving that our engineers are able to deliver a cutting-edge scientific instrument, and that our scientists are able to use it for frontier science,” Science and Technology Minister Derek Hanekom said in a statement on Thursday.
“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 10 years.”
Giant outbursts from binary star system
According to SKA South Africa, local and international astronomers using the KAT-7 telescope in the Karoo along the existing 26-metre radio telescope at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) near Johannesburg, have observed “a neutron star system known as Circinus X-1 as it fires energetic matter from its core in extensive, compact jets that flare brightly”.
The details of the flares are visible only in radio waves.
Circinus X-1 is a two-star system in which one of the companion stars is a high-density neutron star – an extremely dense and compact remnant of an exploded star, only about 20 kilometres in diameter. When the two stars are at their closest in their elliptical orbit, the gravity of the dense neutron star pulls material from the companion star, causing a powerful jet of material to blast out from the system.
When KAT-7 observed Circinus X-1 between December 2011 and January 2012, the system flared twice at levels among the highest observed in recent years. KAT-7 was able to catch both these flares and follow them as they progressed – the first time that the system has been observed in such detail during multiple flare cycles.
“One way of explaining what is happening is that the compact neutron star gobbles up part of its companion star and then fires much of this matter back out again,” said Dr Richard Armstrong, a SKA Fellow at the University of Cape Town and lead author of the paper reporting these results.
“The dramatic radio flares happen when the matter Circinus X-1 has violently ejected slows down as it smashes into the surrounding gas.”
At the same time, Circinus X-1 was being observed at HartRAO at two higher frequencies as part of a long-term study of this object. HartRAO Emeritus Astronomer Dr George Nicolson, a pioneer of radio astronomy in South Africa, said the flares were much stronger at the higher frequencies, “and by combining the three sets of measurements, we could study how each flare evolved as time progressed and investigate details of the turbulent interactions of the jet.
“These types of observations help us to understand how matter is accreted onto extremely dense systems, such as neutron stars and black holes,” Armstrong said. “They also shed light on how neutron stars are able to generate these powerful outflows and associated radio bursts.”
Development of the ThunderKAT project
According to Professor Justin Jonas, associate director for science and engineering at SKA South Africa, the KAT-7 telescope was built as an engineering test bed to refine the design and systems for the MeerKAT telescope, “but we are absolutely delighted that it has turned out to be a top quality science instrument, capable of producing significant science.
“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,” Jonas said.
The observations and analysis that went into the paper accepted for publication involved collaborative work by scientists from SKA South Africa along with local and international universities.
This work forms part of the development of the ThunderKAT project on MeerKAT, which aims to find many more of these types of systems in the galaxy, and to search for new types of radio systems that change rapidly with time.
According to the two leaders of the ThunderKAT project, Professor Rob Fender of the University of Southampton in the UK and Professor Patrick Woudt of the University of Cape Town, the project will search for all types of radio bursts and flashes in KAT-7 and MeerKAT data on timescales from seconds to years.
Finding and studying the systems that produce these outbursts will allow scientists to test the extremes of physics, and are beyond anything achievable in any laboratory on Earth.
“These systems provide a unique glimpse of the laws of physics operating in extraordinary regimes”, Woudt says, “and nearly all such events are associated with transient radio emissions.”