GRB 221009A also known as Swift J1913.1+1946 was an unusually bright and long-lasting gamma-ray burst (GRB) jointly discovered by the Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope on October 9, 2022. The gamma-ray burst was around seven minutes long, but was detectable for more than ten hours following initial detection, and for several hours was bright enough in visible frequencies to be observable by amateur astronomers. Despite being over 2 billion light-years away, it was powerful enough to affect Earth's atmosphere, having the strongest effect ever recorded by a gamma-ray burst on the planet. The peak luminosity of GRB 221009A was measured by Konus-Wind to be ∼ 2.1 × 1047 J/s and by Fermi-GBM to be ∼ 1.0 × 1047 J/s over the 1.024s interval. A burst as energetic and as close to Earth as 221009A is thought to be a once-in-10,000-year event. It was the brightest and most energetic gamma-ray burst ever recorded, being deemed the "BOAT", or brightest of all time.
Characterization
GRB 221009A came from the constellation of Sagitta and occurred an estimated 1.9 billion years ago, however its source is now 2.4 billion light-years away from Earth due to the expansion of the universe during the time-of-flight to Earth. The burst's high-intensity emissions spanned 15 orders of magnitude on the electromagnetic spectrum, from radio emissions to gamma rays. Radio signals broadcast by the winding down of whatever process created the initial burst will likely linger for years to come. This broadband emission offers the rare opportunity to study normally-fleeting GRBs in great detail.
Observation
The burst saturated the Fermi Gamma-ray Space Telescope's detector, which captured gamma ray photons with energies exceeding 100 GeV. GRB 221009A is by far the most productive event for very high energy (VHE) photons ever witnessed by scientific instrumentation. Before GRB 221009A, the number of very high-energy photons detected over the entire history of GRB astronomy numbered only a few hundred. When the burst's radiation arrived at Earth the Large High Altitude Air Shower Observatory (LHAASO) alone saw more than 5,000 such VHE photons. Some of these photons arrived at Earth carrying a record 18 TeV of energy, more than can be produced at the Large Hadron Collider (LHC) at the European Center for Nuclear Research (CERN). Russia's Carpet-2 facility at the Baksan Neutrino Observatory may have also recorded a single 251-TeV photon from this burst. These detected energies are far more than GRB 190114C, which had up to 1 TeV of energy, which was deemed to have been the biggest explosion since the Big Bang, or GRB 190829A, which had up to 3.3 TeV of energy, being the first and only GRB so far to have photons above 10 TeV. The burst possibly had the signature of accelerating ultra-high-energy cosmic rays for the first time.
GRB 221009A was subsequently observed by the Neutron Star Interior Composition Explorer (NICER), The Monitor of All-sky X-ray Image (MAXI), the Imaging X-ray Polarimetry Explorer (IXPE), The International Gamma-ray Astrophysics Laboratory (INTEGRAL), the XMM-Newton space telescope, The Large High Altitude Air Shower Observatory (LHASSO) and many others.
Possible causes
GRB 221009A may have been caused by a massive star undergoing a supernova, or by the birth of a black hole. Supernovae often lead to the formation of a black hole if the parent star is too massive for stable neutron star formation, and it is not yet known which part of, or whether, the death of a star was responsible for this gamma-ray burst. Some physicists speculate that the exceptionally high-energy photons observed during 221009A could be the result of previously theoretical or unknown physical processes involving dark matter, axions, or decaying sterile neutrinos. As yet there is no conclusive evidence that this gamma-ray burst was caused by a supernova; nor have any of the enormous number of neutrinos emitted by supernovae been detected. Lightning detectors in India and Germany picked up signs that the Earth's ionosphere was perturbed for several hours by the burst, though only mildly, as well as an enormous influx of electrically charged particles, showing just how powerful it was. It also disrupted longwave radio communications. It had the strongest affect ever recorded by a gamma-ray burst on the planet. Further, the relativistic jet of this gamma-ray burst has an unusual structure.