Pathfinders: Highlights from SKA precursor and pathfinder facilities around the world

Promising beginnings for Australia’s newest supercomputer

BY KARINA NUNEZ (PAWSEY SUPERCOMPUTING CENTRE)

Australia’s newest supercomputer, Setonix, has produced a highly detailed image of a supernova remnant immediately after the computing system’s first stage was made available to researchers.

Data used to create the image was collected with the ASKAP radio telescope, an SKA precursor owned and operated by Australia’s national science agency CSIRO, on Wajarri Yamatji Country in Western Australia. That data was then transferred to the Pawsey Supercomputing Research Centre in Perth, where Setonix is located, via high-speed optical fibre.

The supernova remnant was imaged in exquisite detail using data from the ASKAP radio telescope.

Credit: Dr Wasim Raja/CSIRO, Dr Pascal Elah/Pawsey

Within 24 hours of accessing the first stage of Pawsey’s new Setonix system, CSIRO’s ASKAP science data processing team began integrating their processing pipeline into the new system.

Setonix (named after the quokka - Setonix brachyurus - a beloved small marsupial native to Western Australia) is the key part of a AU$70 million capital upgrade of the Pawsey Centre.

The new supercomputer is being installed in two stages. The first stage is underway, and the second stage is expected to be completed later this year.

Dr Pascal Elahi, Pawsey’s supercomputing applications specialist, said deploying this first phase of Setonix has increased the computing power of the Pawsey Centre by 45%.

“Processing data from ASKAP’s astronomy surveys is a great way to stress-test the Setonix system and see what is possible,” Dr Elahi said.

While Setonix is ramping up to full operations, so is ASKAP, which is currently wrapping up a series of pilot surveys and will soon undertake even larger and deeper surveys of the sky. Setonix will be used to process the data collected by ASKAP.

Dr Wasim Raja, a researcher on CSIRO’s ASKAP team, said the supernova remnant’s dataset was selected to test the processing software on Setonix, given the challenges involved in imaging such a complex object.

“Setonix’s large, shared memory will allow us to use more of our software features and further enhance the quality of our images. This means we will be able to unearth more from the ASKAP data,” Dr Raja said.

When fully operational, Setonix will be up to 30 times more powerful than Pawsey’s earlier Galaxy and Magnus systems combined. This will allow for more processing of the vast amounts of data coming in from many projects, and more science will be achieved in a fraction of the time.

SKA precursor telescopes don ‘sunglasses’ to find brightest ever pulsar

BY RACHEL RAYNER (CSIRO)

An international research team has used a new observation technique to discover the brightest extragalactic pulsar known, and it could even be the most luminous one ever found. The findings have been published in The Astrophysical Journal.

A pulsar is a rapidly rotating neutron star – a remnant of a dead star - that emits two beams of circularly polarised radio light. As the beams flash across space they create a unique timing and polarisation signature. Around 3,000 pulsars have been detected inside our galaxy, while those in neighbouring galaxies, the Large Magellanic Cloud and Small Magellanic Cloud, only number around 30. This may be because they have fewer pulsars, being smaller dwarf galaxies compared to our own, but most pulsars would also be too faint for our telescopes to detect at that distance (around 200,000 light years away).

Traditional methods of finding pulsars look for the flickering time signature in telescope data but can miss those that are too fast or too slow.

The research team instead applied a new method of seeking out pulsars to CSIRO’s ASKAP radio telescope. By using the astronomical version of “sunglasses” to capture light that is polarised, they spotted an intriguing light source in the Large Magellanic Cloud. Follow-up observations by SARAO’s MeerKAT telescope in South Africa confirmed that researchers had

found a never-before-seen pulsar that is 10 times brighter than any other detected outside our galaxy.

Collecting circularly polarised light is a highly specialised capability, which only a few of the world’s telescopes have the capacity to achieve. ASKAP and MeerKAT’s sophisticated engineering enables them to observe light that is linear or circularly polarised. By looking for light that is circularly polarised, pulsars outside the standard timing range can be found. The collaboration capitalised on the telescopes’ unique capabilities, namely ASKAP’s high survey speed and MeerKAT’s high resolution. ASKAP can scan large swathes of sky in this mode and then researchers, noticing anything unusual, can set MeerKAT to have a closer look.

With this team effort, new discoveries are being made. Before now, the bright spot in the radio data was overlooked as a distant galaxy.

Read the paper: https://iopscience.iop.org/article/10.3847/1538-4357/ac61dc

CSIRO acknowledges the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site where ASKAP is located.

A section of the Large Magellanic Cloud, captured under normal conditions by SARAO’s MeerKAT radio telescope. It is detecting all radio light, and the pulsar looks like just another source of radio light.

Credit: Yuanming Wang

The polarised light from a section of the Large Magellanic Cloud, as captured by SARAO’s MeerKAT radio telescope. In this field, MeerKAT was looking for sources that produced light that is circularly polarised. Very few objects in the sky produce this type of polarised light – pulsars being one of them.

Credit: Yuanming Wang

Astronomers detect galactic space laser

BY ICRAR

A powerful radio-wave laser, called a “megamaser”, has been observed by the MeerKAT telescope in South Africa.

The record-breaking find is the most distant megamaser of its kind ever detected, at about five billion light-years from Earth. The light from the megamaser has travelled 58 thousand billion billion (58 followed by 21 zeros) kilometres to Earth.

Artist’s impression of a hydroxyl maser. Inside a galaxy merger are hydroxyl molecules, composed of one atom of hydrogen and one atom of oxygen. When one molecule absorbs a photon at 18cm wavelength, it emits two photons of the same wavelength. When molecular gas is very dense, typically when two galaxies merge, this emission gets very bright and can be detected by radio telescopes such as the MeerKAT.

Credit: IDIA/LADUMA using data from NASA/StSci/SKAO/ MolView

The discovery was made by an international team of astronomers led by Dr Marcin Glowacki, who previously worked at the Inter-University Institute for Data Intensive Astronomy and the University of the Western Cape in South Africa. The paper has been accepted for publication in The Astrophysical Journal Letters and is available as a preprint: https://arxiv.org/abs/2204.02523

Dr Glowacki, who is now based at the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) in Western Australia, said megamasers are usually created when two galaxies violently collide in the Universe.

“When galaxies collide, the gas they contain becomes extremely dense and can trigger concentrated beams of light to shoot out,” he said. “This is the first hydroxyl megamaser of its kind to be observed by MeerKAT and the most distant seen by any telescope to date. It’s impressive that, with just a single night of observations, we’ve already found a record-breaking megamaser. It shows just how good the telescope is.”

The record-breaking object was named “Nkalakatha” [pronounced ng-kuh-la-kuh-tah] – an isiZulu word meaning “big boss”.

Nkalakatha’s host galaxy as viewed from Perth, Western Australia. It’s ~5 billion light years away and invisible to the naked eye, between Archernar and Aldebaran.

Credit: ICRAR

Dr Glowacki said the megamaser was detected on the first night of a survey involving more than 3,000 hours of observations by the MeerKAT telescope.

The team is using MeerKAT to observe narrow regions of the sky extremely deeply and will measure atomic hydrogen in galaxies from the distant past to now. The combination of studying hydroxyl masers and hydrogen will help astronomers better understand how the Universe has evolved over time.

“We have follow-up observations of the megamaser planned and hope to make many more discoveries,” Dr Glowacki said.

Strange slow-spinning neutron star discovered in ‘stellar graveyard’

Artist impression of the 76s pulsar (in magenta) compared to other more rapidly spinning sources.

Credit: Danielle Futselaar (artsource.nl)

BY DR HILARY KAY AND BEN ROBINSON (THE UNIVERSITY OF MANCHESTER)

An international team of scientists, led by members of the European Research Council funded MeerTRAP group at The University of Manchester in the UK, has discovered an unusual, very slow-spinning neutron star using South Africa’s MeerKAT telescope.

The star, named PSR J0901-4046, is rotating once every 76 seconds and is unexpectedly emitting radio pulses.

Neutron stars (also known as pulsars) are extremely dense remnants of the supernova explosion of a massive star. They produce beams of radio waves that sweep across the sky as they spin, producing regular flashes like cosmic lighthouses. However, slow rotation along with a strong magnetic field, like that seen with PSR J0901-4046, is thought to inhibit radio emission, casting uncertainty on the exact nature of the object.

Whilst the radio energy produced by PSR J0901-4046 is characteristic of a pulsar, the chaotic structure within the pulses and their polarisation is similar to that seen in magnetars, and the spin rate is more consistent with that of a white dwarf. One possibility, the team suggests, is that it may belong to a new class of ultra-long period neutron stars.

PSR J0901-4046 was first discovered serendipitously when a single pulse was detected by the MeerTRAP instrument, which was piggybacking on observations by the ThunderKAT project. Combining data from both projects enabled the teams to accurately locate the position of the neutron star, allowing for more detailed and sensitive follow-up observations.

The high sensitivity of MeerKAT observations, along with MeerTRAP’s ability to detect transients in real time and the simultaneous imaging from the ThunderKAT team, combined to make the discovery possible. In the case of PSR J0901-4046, radio emission was only detected for a tiny fraction (0.5%) of its rotation period and therefore detecting similar sources will be observationally challenging.

Dr Manisha Caleb, formerly from The University of Manchester and now at the University of Sydney, Australia, who led the research said: “It is likely there are many more of these very slowly spinning sources in the galaxy which has important implications for how neutron stars are born and age. The majority of pulsar surveys do not search for periods this long and so we have no idea how many of these sources there might be.”

For now, the exact mechanisms behind the radio emission from PSR J0901-4046 remain a mystery. But with the unprecedented sensitivity of the next generation of radio telescopes like the SKA, coupled with the innovative techniques like those employed by scientists in the MeerTRAP team, previously unseen new classes of radio transients will be uncovered, advancing our understanding of the relationship between neutron stars, ultra-long period magnetars and fast radio bursts.

The paper, “Discovery of a radio-emitting neutron star with an ultra-long spin period of 76s”, is published in Nature Astronomy: https://www.nature.com/articles/s41550-022-01688-x

The Dwingeloo Test Station: a major milestone towards LOFAR2.0

Compilation of pictures of the DTS Opening event on the ASTRON premises on 10 May 2022. The speakers (from top left to bottom right) are ASTRON director Prof. Jessica Dempsey; LOFAR2.0 Station Development Project Manager Arno Schoenmakers; and LOFAR2.0 Project Scientist Prof. Jason Hessels.

Photos courtesy of Adriaan Renting and Mark Ruiter (ASTRON).

BY PROF. JASON HESSELS (ASTRON)

A major upgrade to the Low Frequency Array (LOFAR) is now a step closer following the opening of the new Dwingeloo Test Station (DTS) in the Netherlands, which will test prototype software and hardware for LOFAR2.0.

LOFAR is a pan-European radio telescope that links tens of thousands of antennas across 10 partner countries, an enormous geographical span which allows it to make remarkably sharp images. The low-band antennas (LBA) and high-band antennas (HBA) provide a powerful view of the lowest radio frequencies visible from Earth: from 10- 240 MHz.

At the time of construction, the available computational power meant that it was only possible to use either the LBA or HBA antennas at any given time. With LOFAR2.0, it will be possible to use all the LOFAR antennas at once and to expand the field-of-view of the stations. This is made possible by an order-of-magnitude increase in the computing power at the LOFAR stations, as well as a new central computational “brain”, the COBALT2.0 correlator and beam-former. Furthermore, a new White-Rabbit-based clock distribution system is being installed such that there

are no timing delays between the 38 Dutch LOFAR stations. [White Rabbit is a technology that provides extremely accurate (nanosecond level of accuracy) timing over the network. It can be used to provide timing to the antennas so that data from each receptor can be accurately timestamped. It is also being used by the SKAO for its telescopes.]

On 10 May, the Dwingeloo Test Station was ceremoniously opened. Located next to ASTRON, it is testing the entire LOFAR2.0 signal chain: from the antennas, through the new receiver boards and Uniboard-squared-based processing, all the way to the correlator and beam-former. This is a crucial step in the development process because it allows the prototype electronics, firmware and software to be tested before being rolled out to a full LOFAR station and then the entire array.

The team has already achieved the “first fringes” between test antennas [showing they can operate as an array], as well as multi-day stability tests with all LBA and HBA antennas observing simultaneously. This progress means the first full LOFAR2.0 station is on track for delivery by early 2023.

These enhancements are being implemented from 2021-2024, and together will provide a step function in LOFAR’s overall scientific capabilities. It will remain a unique and world-leading telescope, also accessing the largely unexplored spectral window below 50 MHz.

Early LOFAR2.0 science observations are planned to begin in 2025, affording ultra-wide-band, ultra-deep, ultra-high resolution observations. Among the many scientific goals for LOFAR2.0, such observations can track the history of star formation and galaxy evolution over cosmic time, as well as identify starplanet interactions in our own galaxy.