Locals look at brightest burst
Australian astronomers have observed a gamma ray burst brighter than any seen before.
A new study provides vital information in the global effort to understand the brightest-ever detected gamma ray burst, which swept through the Solar System on 9 October last year.
Detailed findings of the explosion from a galaxy 1.9 billion light years away have been published in The Astrophysical Journal Letters.
PhD student James Leung from the University of Sydney says: “The exceptional brightness of this gamma-ray burst meant astronomers were able to study it in unprecedented detail in real-time as the light arrived from that distant galaxy”.
“This gave us a golden opportunity to test intricate physical models that describe what happens before, during and after the death of a star.”
Mr Leung is co-author of a complementary study published on the online arXiv and submitted for publication in Nature Astronomy.
Scientists believe gamma ray bursts - the biggest known explosions in the Universe - are the death throes of enormous stars as they collapse into black holes, emitting enormous amounts of energy in opposite directions as gamma rays and X-rays.
At the time of its detection last year, the gamma ray burst GRB 221009A was dubbed as BOAT - the brightest of all time.
“While that’s a bit of an exaggeration, GRB 221009A was likely the brightest burst at X-ray and gamma-ray energies to occur since human civilisation began,” said study co-author Professor Eric Burns.
The burst was so bright it blinded most gamma-ray instruments in space, which meant they could not measure the real intensity of the emission.
Astronomers believe it to be a one in 10,000-year event. While the energy from this gamma ray burst was not unusually large, the jets of energy were exceptionally narrow with one pointed directly at Earth, making it appear exceptionally bright.
Working with scientists from the University of Oxford, the University of Sydney and the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), the astronomers provided vital and rapid follow-up observation of the cosmic event in the radio wave part of the electromagnetic (light) spectrum.
This supported work by US astronomers piecing together missing data in shorter wavelengths (X-ray and gamma ray) using NASA’s Fermi Gamma-ray Space Telescope and data collected from Russian and Chinese teams. Together they showed the burst was 70 times brighter than any seen before.
University of Sydney scientists provided follow-up observation of the gamma ray burst using the CSIRO ASKAP telescope in Western Australia, detecting the effects of the dramatic emission of energy at longer radio wavelengths.
“One of the fascinating things about gamma ray bursts is, although they are over quite quickly - in just a matter of seconds - they leave afterglow emissions across the light spectrum in surrounding matter that echo for months and years afterwards,” says Professor Tara Murphy, Head of the School of Physics at the University of Sydney.
This afterglow is produced by a forward shock from the material ejected by the gamma-ray burst and a reverse shock reflected backwards into the ejected material.
The observations showed a rapid, early brightening from the source of the event caused by the reverse shock of the gamma ray burst. This revealed evidence in radio waves that is difficult to explain within current theoretical explanations of gamma ray bursts.
Scientists must now refine and develop new theoretical models to understand these most extreme explosions in the Universe.
No gamma ray burst has so far been detected in the Milky Way galaxy.
It has been predicted that if such an enormous explosion were to happen relatively close to Earth - and pointed in the planet’s direction - the gamma ray burst could knock out electronics or, at worst, strip Earth of its atmosphere leading to mass extinctions.