New clues about brightest and most energetic gamma-ray burst ever detected

In October 2022, a gamma-ray burst (GRB), called GRB 221009A, was detected and it was so bright that astronomers quickly dubbed it the BOAT – the brightest of all time - with follow-up studies showing that it was 70 times brighter and far more energetic than the previous record holder.

Now, researchers have got clues from NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) observatory that the jet created by gamma-ray burst 221009A had some unique features, hinting at potential influences from the progenitor star's physical properties. Alternatively, an entirely novel mechanism might launch these exceptionally bright jets into space.

GRBs are the most energetic form of light in the universe, invisible to the human eye. While all known GRBs originate in galaxies beyond our Milky Way, their luminosity allows them to be detected billions of light-years away. 

"This event was so much brighter and more energetic than any gamma-ray burst we’ve seen before, it’s not even close. Then, when we analyzed the NuSTAR data, we realized that it also has this unique jet structure. And that was really exciting because we have no way of studying the star that produced this event; it's gone now. But we now have some data giving us clues about how it exploded," said Brendan O’Connor, lead author of the new study and an astronomer at George Washington University in Washington.

GRB 221009A blinded most gamma-ray instruments in space with its extraordinary brightness. However, U.S. scientists managed to reconstruct the event's true luminosity using data from NASA's Fermi Gamma-ray Space Telescope.

Similar to other gamma-ray bursts, the jet produced by GRB 221009A emerged from the collapsing star, resembling a forceful discharge from a fire hose. Gamma rays radiated from the hot gas and particles at the core of the jet. While in previous observations, GRBs displayed highly compact jets with minimal stray light or material beyond the narrow beam, GRB 221009A's jet had a narrow core with wider, sloping sides.

According to the researchers, similar properties have been observed in some highly energetic gamma-ray bursts, but the BOAT's jet presented an unprecedented characteristic. The energy of the material within the jet varied, indicating that the material's energy changed as it moved away from the core. This phenomenon had never been witnessed before in a long gamma-ray burst jet.

Due to the enormous distance to gamma-ray bursts, astronomers are unable to directly capture images of the jets. Instead, they must interpret the light emitted by these events to glean information about their physical properties. It can be likened to studying footprints in the snow to deduce the characteristics of the person who made them.

"There are multiple X-ray telescopes operating in space, each with different strengths that can help astronomers understand these cosmic objects better," said Daniel Stern, NuSTAR project scientist at NASA’s Jet Propulsion Laboratory in Southern California.

New clues about the BOAT (Brightest Of All Time)@NASA’s NuSTAR X-ray telescope is providing a tantalizing clue about the brightest and most energetic gamma-ray burst ever detected. Observations show the collapsing star had a unique jet structure. https://t.co/dWgtXv8C72 pic.twitter.com/p7mOSR7lnG

— NASA JPL (@NASAJPL) June 8, 2023