On October 9, 2022, NASA’s Swift satellite captured a high-intensity burst of gamma-ray emission from a galaxy 1.9 billion light-years away. Dubbed the “BOAT” – “the brightest ever”, GRB 221009A was so extraordinarily powerful that it sent shock waves into the Earth’s ionosphere, the outer layer of our planet’s atmosphere.

“If it was any closer, it would be very bad,” says astronomer Brendan O’Connor of George Washington University.

Such a “long” GRB (meaning that a gamma-ray burst can take several minutes) is usually the result of the death of a massive star with a mass of 8 to 30 times our Sun. When the core runs out of fuel, the star contracts and then collapses to form a neutron star or black hole. In the process, the outer layers of the stellar cavern twist around it and form a rotating disk of gas, which is then swept away by strong magnetic fields and emitted into two powerful jets moving at near the speed of light. Charged particles orbiting magnetic fields in these jets emit gamma rays.

While most such gamma-ray bursts occur much further away, GRB 221009A’s relative proximity has given astronomers an unprecedented glimpse into its central engine. In fact, the combination of intense brightness and proximity is so rare that astronomers don’t expect to see such a burst of gamma rays for another 1,000 years, on average.

“We probably knew we would never have this opportunity again,” says Gokul Srinivasaragavan. Student at the University of Maryland.

O’Connor and Srinivasaragavan, authors of two papers on the discovery, observed the eruption associated with GRB 221009A using the Gemini South Telescope, half of the Gemini International Observatory operated by NSF’s NOIRLab.

an article published Science Advances explores the “opening angle” of the GRB jet, which can provide information about the process that produces the gamma rays. second article published Astrophysical Journal Letters, Explains the search for supernovae, the optical analog of the GRB.

As a rule, gamma-ray jets from GRBs are quite narrow, which means relatively few of them are aimed at us. This limits the number of GRBs we can detect; If they are not pointed approximately at us, we cannot detect them. This narrow opening angle is the result of tightly wound magnetic fields that impede particle flow. However, the GRB 221009A was different. Using the Gemini Southern Multi-Object Spectrograph (GMOS) instrument, O’Connor’s team determined that GRB 221009A’s jet had a shape not seen in other gamma-ray burst jets.

The jet had a narrow core surrounded by wide, curved wings. These features are not widely observed, which is surprising because if these wing-like jets were common, astronomers would expect to have seen more of them by now. Rather, these broad wings should be as rare as the shiny GRB 221009A.

“There must be something specific about these large jets that are unique to supermassive GRBs,” says O’Connor. “This particular jet shape may be the signature of the most powerful eruptions and explains why we continue to see its optical and infrared glow for months after the eruption.”

Speaking of optical glow, Srinivasaragavan pioneered the search for a companion supernova – visible light from the explosion of a star. Using the GROWTH-India Telescope, Lowell Discovery Telescope in Arizona and the Liverpool Telescope in Tenerife, Spain, as well as Gemini South, Srinivasaragavan’s group was able to find evidence of the supernova now known as SN 2022xiw. Supernova SN 2022xiw turned out to be surprisingly striking and not so different from other supernovas.

“We found that the supernova associated with the collapse of the core of GRB 221009A was not more energetic or brighter than other long gamma-ray bursts previously studied,” says Srinivasaragavan. “This contradicts our naive expectation that a more powerful long gamma-ray burst will result in a more powerful core collapse supernova.”

Based on the brightness of the supernova, Srinivasaragavan and O’Connor calculated that the stellar explosion ejected matter with a mass of 3.5 to 11.1 solar masses. That’s up to 11 suns of material that explodes in a matter of seconds, releasing more energy in that time than the sun has produced in its entire lifetime.

The details with which astronomers can observe GRB 221009A will provide a better understanding of the mechanism that creates a long GRB when a massive star reaches the end of its life. It could also become a kind of “rosette stone” for future super-universal gamma-ray bursts to be observed at great distances. Until then, Srinivasaragavan says the rarity of the GRB 221009A means it will live on in memories for a long time. “This has been one of the most exciting events in recent history for the astrophysics community as a whole.” Source