GRB 221009A. The brightest of all time.

  

  

This sequence constructed from Fermi Large Area Telescope data reveals the sky in gamma rays centered on the location of GRB 221009A. Each frame shows gamma rays with energies greater than 100 million electron volts (MeV), where brighter colors indicate a stronger gamma-ray signal. In total, they represent more than 10 hours of observations. The glow from the midplane of our Milky Way galaxy appears as a wide diagonal band. The image is about 20 degrees across. 

Credit: NASA/DOE/Fermi LAT Collaboration  

One of the most powerful explosions ever recorded, Gamma-Ray Burst GRB 221009A, was detected on October 9, 2022, by X-ray and gamma-ray space telescopes, including NASA's Fermi Gamma-ray Space Telescope, Neil Gehrels Swift Observatory, and the Wind spacecraft. The Gamma-ray Burst Monitor on board the Fermi satellite triggered and located the burst at 13:16:59.99 UT. This was the brightest ever detected burst by the measures of peak flux (0.031 erg s⁻¹ cm⁻²) and fluence (0.21 ± 0.02 erg cm⁻²).  The burst was actually first detected on October 8, when Voyager 1 spacecraft registered significant counts in its particle detectors for a brief time. As the gamma-ray burst swept through the Solar System it was detected by instruments on more than a dozen satellites built for astrophysics, planetary science, and solar observations, and 19 hours after arrival at Voyager 1, the burst arrived at Earth.

   GRB 221009A occurred approximately 1.9 billion light-years away in the direction of the constellation Sagitta. It was the most energetic and one of the nearest gamma-ray bursts (GRBs) ever observed, and astronomers quickly dubbed it the BOAT – the brightest of all time. Current estimates put the energy of the GRB at ∼1.2 × 10⁵⁵ erg – in contrast, the total energy released by the Sun throughout its lifetime is expected to be about 10⁵¹ erg. It is estimated that such a powerful burst may occur roughly every 10,000 years, and it may be the brightest gamma-ray burst since human civilization began. GRB 221009A was so intense that it temporarily blinded multiple sensitive gamma-ray detectors in space. The gamma-ray burst lasted for more than ten hours since detection and telescopes around the world turned to the site to study the aftermath.

   This event likely belongs to the class of long GRBs, the end-of-life phase of an extremely rare set of massive stars. Once a massive star reaches a point in which the nuclear reactions in its core can no longer produce enough energy to support it, it collapses. If that star is rotating rapidly, the explosion releases material into space in the form of two opposite and narrow jets moving just shy of the speed of light. And if one of those jets points toward us, we see a burst of gamma rays, typically lasting for several minutes. A longer-lived fading afterglow, observable across the electromagnetic spectrum, often follows the initial burst. 

 

A view of GRB 221009A from the Gemini South telescope in Chile. The image is a combination of 4 exposures in I, J, H, K with two instruments taken on 14 October 2022. GRB 221009A is the pink dot towards the centre of the image.
Credit: International Gemini Observatory/NOIRLab/NSF/AURA/B. O'Connor (UMD/GWU) & J. Rastinejad & W Fong (Northwestern Univ) Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller, M. Zamani & D. de Martin (NSF’s NOIRLab) 

 

The Hubble Space Telescope’s Wide Field Camera 3 revealed the infrared afterglow (circled) of GRB 221009A and its host galaxy, seen nearly edge-on as a sliver of light extending to the burst's upper left. This composite incorporates images taken on Nov. 8 and Dec. 4, 2022, one and two months after the eruption. Given its brightness, the burst’s afterglow may remain detectable by telescopes for several years. The picture combines three near-infrared images taken each day at wavelengths from 1 to 1.5 microns.
Credit: NASA, ESA, CSA, STScI, A. Levan (Radboud University); Image Processing: Gladys Kober 

 

   The burst also enabled astronomers to probe distant dust clouds in our own galaxy. As the prompt X-rays traveled toward us, some of them reflected off of dust layers, creating extended “light echoes” of the initial blast in the form of X-ray rings expanding from the burst’s location. The X-ray Telescope on NASA’s Neil Gehrels Swift Observatory discovered the presence of a series of echoes. Detailed follow-up by ESA’s XMM-Newton telescope, together with Swift data, revealed these extraordinary rings were produced by 21 distinct dust clouds located between 700 and 61,000 light-years away.

   GRB 221009A was so bright that it was affecting Earth, even from billions of light years away. Naval radio transmitters recorded a strange disturbance in the upper atmosphere, which seems to have been caused by the powerful light from the GRB slamming into it. Detectors that search for high-energy photons have also seen extraordinary particles with energies far higher than anything produced at the Large Hadron Collider – the Large High Altitude Air Shower Observatory (LHAASO), a Cherenkov observatory in China, has detected photons with energies up to roughly 18 teraelectronvolts (TeV). 

 

Swift’s X-Ray Telescope captured the afterglow of GRB 221009A about an hour after it was first detected. The bright rings form as a result of X-rays scattered by otherwise unobservable dust layers within our galaxy that lie in the direction of the burst. The dark vertical line is an artifact that comes from a dead column of pixels in the camera. Credit: NASA/Swift/A. Beardmore (University of Leicester) 

XMM-Newton images recorded 20 dust rings, 19 of which are shown here in arbitrary colors. This composite merges observations made two and five days after GRB 221009A erupted. Dark stripes indicate gaps between the detectors. A detailed analysis shows that the widest ring visible here came from dust clouds located about 1,300 light-years away. The innermost ring arose from dust at a distance of 61,000 light-years – on the other side of our galaxy. GRB221009A is only the seventh gamma-ray burst to display X-ray rings, and it triples the number previously seen around one.

Credit: ESA/XMM-Newton/M. Rigoselli (INAF) 

 

This chart compares the GRB 221009A's prompt emission to that of four previous record-holding long gamma-ray bursts. GRB 221009A was so bright it effectively blinded most gamma-ray instruments in space, but U.S. scientists were able to reconstruct its true brightness from Fermi data.
Credit: NASA's Goddard Space Flight Center and Adam Goldstein (USRA)

 

 

   Cosmological gamma-ray bursts are powerful flashes of energetic gamma-rays lasting from less than a second to several minutes. They release a tremendous amount of energy in this short time making them the most powerful events in the Universe since the Big Bang. Cosmological GRBs arise from bipolar, relativistic jets powered by compact central engines. These jets undergo internal dissipation releasing the prompt GRB emission in the keV and MeV regimes and subsequently interact with the circumburst material to develop an external shock that releases synchrotron emission across the electromagnetic spectrum, referred to as afterglow.

   There are two distinct varieties of GRBs, which are now known to have different progenitor systems. Events with a duration of less than about two seconds are classified as short gamma-ray bursts. These account for about 30% of gamma-ray bursts. The mean duration of these events are 0.2 seconds. Short bursts are believed to originate from the merger of binary neutron stars, or a neutron star with a black hole. Such mergers are theorized to produce kilonovae. Most observed events (70%) have a duration of greater than two seconds and are classified as long gamma-ray bursts. They are thought to be mostly associated with the explosion of stars that collapse into black holes (collapsars), a rare, fast-rotating subset of core-collapse supernovae. In the explosion, two jets of very fast-moving material are ejected. If a jet happens to be aimed at Earth, we see a brief but powerful gamma-ray burst. These events are also called hypernovae.

  

This illustration shows the ingredients of a long gamma-ray burst, the most common type. The core of a massive star (left) has collapsed, forming a black hole that sends a jet of particles moving through the collapsing star and out into space at nearly the speed of light. Radiation across the spectrum arises from hot ionized gas (plasma) in the vicinity of the newborn black hole, collisions among shells of fast-moving gas within the jet (internal shock waves), and from the leading edge of the jet as it sweeps up and interacts with its surroundings (external shock). 

Credit: NASA's Goddard Space Flight Center

 

References:

Eric Burns. Focus on the Ultra-luminous Gamma-Ray Burst GRB 221009A. The Astrophysical Journal Letters. March 2023
Eric Burns et al. GRB 221009A: The BOAT. The Astrophysical Journal Letters. 946 (1)
NASA: NASA’s Swift, Fermi Missions Detect Exceptional Cosmic Blast
NASA: NASA Missions Study What May Be a 1-In-10,000-Year Gamma-ray Burst

 

 

© 2025, Andrew Mirecki