Capturing the unseen: SETI Institute and Oxford University astronomers discover early radio emission from a spectacular cosmic explosion

A team of astronomers from the SETI Institute, the University of Oxford, and other institutions has worked together using the Allen Telescope Array (ATA) as part of a global effort to observe and understand a massive gamma radio burst.

The team worked together to study the earliest stages of the Universe’s most powerful explosions and was able to capture detailed information about a gamma radio burst (GRB) called the ‘Brightest of All Time’ (BOAT), also known as GRB 221009A.

The international team recorded radio emissions just three hours after the explosion, providing unparalleled insight into the jet’s properties as it rapidly evolved.

The research team included astronomers from the UK, USA, Australia, the Netherlands, Italy, and South Africa. They used data from radio telescopes worldwide, including ATA, to investigate the violent interaction between the jet and circumstellar medium.

These observations offer a rigorous testing ground for theoretical predictions about this interaction, and they provide valuable information for future rapid response instruments.

See also: First gamma-ray eclipses from ‘spider’ star systems detected


First radio telescopes


ATA project scientist, Dr Wael Farah said: “It’s exciting to witness the ATA participating in a worldwide effort to study one of the most interesting and bright supernova explosions.

“We owe this success to the original specification of the ATA and the refurbishment programme that transformed its analogue and digital capabilities.”

The ATA was one of the first radio telescope instruments to record data on this source, only a few hours after the event happened.

Thanks to the rapid response from the ATA team and the unique capabilities of the ATA’s receivers and digital systems, the scientists have been able to shed new light on the physical mechanisms at play in GRBs in unprecedented detail.

In particular, the ATA observations, combined with higher frequency observations conducted with the Arcminute Microkelvin Imager Large Array (AMI-LA) telescope in the United Kingdom, provided the most detailed characterisation yet realised of the ‘reverse shock’ process in GRB explosions.

The reverse shock is a back-propagating ‘echo’ as the relativistic blast wave from the initial explosion slams into surrounding gas and dust.


10,000-year event


The results showcase the effectiveness of the ATA as a fast follow-up machine for astrophysical phenomena, a specification that makes the telescope unique for astronomy (which includes SETI). The ATA has also joined a world-wide effort to study this interesting astrophysical source.

Dr Joe Bright and Dr Lauren Rhodes, two post-doctoral researchers from Oxford, led the research.

Rhodes said: “GRB 221009A is a once in 10,000 years event and is allowing us to understand GRB physics in a way not possible previously.”

Bright added: “Our ability to rapidly respond to this event with a range of radio telescopes has been instrumental in understanding the early-time behaviour of relativistic jets and demonstrates the importance of such observing flexibility when developing new facilities,” said Bright.

The most powerful explosions in the Universe occur because of the death of massive stars, heralding the formation of a black hole or neutron star.

These so-called compact objects can facilitate the launch of highly collimated ejections moving close to the speed of light, known as a jet.

Gamma-ray satellites, dedicated to the early discovery of such events via the detection of high energy bursts of radiation (known as gamma-ray bursts; GRBs), enable us to point other telescopes and study the interaction of the jet as it interacts with the material surrounding the dying star.

On October 9, 2022, the Fermi satellite detected the GRB of record-breaking brightness, GRB 221009A.

This event was the perfect combination of being incredibly energetic and nearby, making it the ideal event for astronomers to study.

The GRB community has been studying the BOAT for the past six months across the entire electromagnetic spectrum, from very low radio frequencies where disturbances were measured in the upper atmosphere up to teraelectronvolt energies, the highest energy photons ever detected from a GRB.

Image: The Allen Telescope Array (ATA) based in Hat Creek Radio Astronomy Observatory, California, USA. The ATA is operated by the SETI institute, designed as an instrument dedicated to techno signature searches, it has the potential to be a powerful facility for the study of transients. © Joe Marfia.