SKA-Low Prototype Used for Radio-Transient Detections

At the end of this decade, one of Australia’s most ambitious and first mega-science project - the Square Kilometre Array (SKA) is going to become fully operational. The powerful radio telescope will commence scanning the low-frequency night sky, helping resolve some of our most fundamental science questions to date. 

But the realm of discovery for the instrument need not wait for many years to produce results, with the telescope’s building, testing and phased approach to introducing antennas, computing and science are expected to reveal new findings along the journey.  

Momentum for the project is now starting to escalate, with the SKA-low (the portion of the telescope that will be built in Australia) having signed the appropriate agreements and contracts in 2020, and early 2021, and procurement call-outs occurring. 

Currently, precursor and pathfinder instruments already exist and are operating to pave the way for the SKA, such as CSIRO’s Australian Square Kilometre Array Pathfinder (ASKAP - developed and operated by Australia’s national science agency, CSIRO) and the Murchison Widefield Array (MWA - led by Curtin University and the International Centre for Radio Astronomy Research (ICRAR)). 

Now, a new paper from an international group of scientists, including several from Australia, outlines a few preliminary results of the first southern-hemisphere all-sky imager and radio-transient monitoring system implemented on two SKA prototypes. 

All-sky monitoring studies give scientists the ability to use wide-angled antennas and telescopes that can see huge amounts of the sky above and around them to search for any new events (known as a transient) that might occur. This is different from a regular telescope (optical or even a large dish antenna for radio) which searches only a small portion of the sky in which the beam or field of view is the focus. 

This kind of research helps astronomers place caps on how often certain events occur, and from what direction they might be coming from (e.g., if events are coming from across the entire sky, then they might be considered universal, whereas when an event only seems to come from the galactic plane - these are considered to be local to our own galaxy. 

This new research paper details how an early-stage transient detection system was implemented and what it found using all-sky images. The paper has been published in Publications of the Astronomical Society of Australia.   

Once constructed, the SKA will become the most powerful telescope in the world, capable of peering deeper into the sky than any other telescope constructed to date. It is made up of two components, both of which complement each other in working towards the science goals for the instrument. 

One component is situated in South Africa and features 197 dish-like antennas, which stretch across an area with the greatest baseline equating to 150 km. This is the SKA-Mid telescope and will scan the sky in the 350 MHz - 1.4 GHz frequency range.  

Across the Indian ocean, Australia will be home to the SKA-Low, which will tune in to 50 MHz – 350 MHz using over 131,000 Christmas-tree like antennas. The SKA-Low will be located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia.

The prototypes are precursors to the SKA, which is Australia’s first mega-science project. The SKA, which was just cleared for construction, will be a massive radio telescope that will span across two countries: Australia and South Africa. 

The SKA prototypes used in this research to detect radio transients were the Engineering Development Array 2 (EDA2) and the Aperture Array Verification System 2 (AAVS2). They were used to find radio transients, which are sources of radio signals that are not constant.  

To detect these radio transients the researchers implemented all-sky imaging and a radio-transient monitoring system. This means that they captured images of large areas of the sky using the radio telescopes and then analysed them to look for bursts of radio activity. 

What they found was the majority of detected transients were due to Radio Frequency Interference (RFI) emissions or reflections from the satellites, aircraft or meteors. Using this wide-field approach, scientists working on the project were able to map out the distribution of satellites above the MRO, showing familiar patterns of where these human-made objects are in orbit (in particular around the equatorial belt) and a series of satellite constellations that snake their way across the field. 

However, this was not always the case and astrophysical sources were also observed using these prototypes.  

Their most interesting detections of astrophysical phenomena were extremely bright pulses from the pulsar PSR B0950+08. A pulsar is a highly magnetised rotating star that emits beams of radiation from its poles. These compact stars, as they rotate, appear to produce periodic pulses of radiation. Detection of this kind of phenomenon will be part of the SKA’s operations when it is up and running.

The results from this paper will enable researchers to further develop and enhance radio-transient detection technology which can then be one day implemented with the full SKA. 

We acknowledge the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site.