A gamma-ray burst that was detected in October 2022 and considered the most powerful on record has been described as a rare event that occurs once in a thousand years. Known as GRB 221009A, it emitted up to 18 teraelectronvolts of energy in its emissions of light. Scientists have been analyzing the burst, and a trio of papers have been submitted to The Astrophysical Journal Letters. The analyses reveal that the burst of light does not conform to theoretical descriptions of how it should behave, indicating that there is something unique about GRB 221009A.
Gamma-ray bursts are the most violent explosions in the Universe, and they release more energy than the Sun would in 10 billion years. They are caused by cataclysmic events such as the supernova or hypernova explosions that occur at the end of massive stars' lifetimes or collisions of binary systems involving at least one neutron star.
Initially, GRB 221009A was thought to be a less powerful flash of X-rays from a relatively nearby source. However, follow-up observations revealed that the burst of light traveled much farther than first thought, covering a distance of 2.4 billion light-years. This distance still makes it one of the closest gamma-ray bursts ever detected, but it also means that it was much more powerful than initially estimated.
Astronomers tracked the evolution of the light curve of GRB 221009A for 73 days following its initial discovery. However, they had to stop observations after around the 70-day mark when the afterglow moved behind the Sun. Scientists expect the afterglow to re-emerge soon.
Astronomers led by Maia Williams from Pennsylvania State University have made an intriguing discovery about the X-ray afterglow of a gamma-ray burst known as GRB 221009A. The team found that the X-ray afterglow was the brightest ever detected by the Swift observatory, by an order of magnitude. However, when distance was factored in, the brightness of GRB 221009A was consistent with other gamma-ray bursts in the Swift catalog. What makes GRB 221009A truly rare is the combination of its characteristics. The team estimates that similar events occur at a rate of less than one per 1,000 years, making this a remarkable opportunity unlikely to be repeated in our lifetime.
Gamma-ray bursts typically produce synchrotron emission, which is the glow of electrons moving at near-light speeds. This occurs as the initial explosion collides with the interstellar medium. The afterglow of GRB 221009A suggests that either the jet structure is more complicated than expected or that it is not narrowly collimated. This could have profound implications for the event's energy budget.
Tanmoy Laskar from the University of Utah led a team of astronomers who suggest that the peculiar afterglow could indicate an additional source of synchrotron emission, or it could mean that something is fundamentally wrong with synchrotron afterglow theory. Another paper, led by astronomer Manisha Shrestha from the University of Arizona, found that the afterglow did not contain some features expected in a supernova explosion. This could mean that most of the energy budget was spent on the jets, leaving little to suggest an exploding star was responsible.
The afterglow of GRB 221009A is expected to re-emerge from behind the Sun soon, and astronomers will be working hard to unravel the mystery of this peculiar explosion in multiple wavelengths.
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