In October 2022, the space-based detector GECAM-C caught the most powerful gamma-ray burst ever seen, GRB 221009A — an explosion that briefly became the brightest source of gamma rays in the sky. But the most interesting part came after: the instrument detected a series of additional flares, and one of them was record-breaking.
This flare released an energy of 1.82×$10^{53}$ erg — more than any known flare following a gamma-ray burst. Its gamma rays were so hard that they reached energies around 300 keV, thousands of times the energy of visible light. For comparison, a hospital X-ray uses photons with energies of tens of keV, while here we're talking about ten times more.
The flare rose and faded very quickly — faster than typical X-ray flares, which are usually seen in soft X-rays or optical. In terms of speed, it resembled the original explosion itself. This is the first observation of a flare in the kiloelectronvolt-to-megaelectronvolt range with sufficiently high time resolution and good statistics.
Such flares help us understand what happens after the main explosion: how material ejected during the collapse of a massive star continues to collide and radiate. The record-breaking flare fills the gap between the primary emission and later, softer flares.
The flare's energy—1.82×$10^{53}$ erg — is equivalent to a supernova explosion, but it was released in seconds, not months.