Free Astronomy Magazine September-October 2025

23 SEPTEMBER-OCTOBER 2025 ASTRO PUBLISHING into the enigmatic and complex na- ture of GRBs at very high energies. The results support theoretical mod- els in which these bursts generate structured, multi-layered jets where particles are accelerated. GRBs are among the Universe’s most powerful phenomena, releasing in just seconds as much energy as the Sun emits over its entire lifetime. As their name suggests, they burst over a brief, prompt phase, lasting sec- onds to minutes, and then are fol- lowed by an afterglow that can fade over hours to months. GRBs are clas- sified as short or long based on the duration of the burst: long GRBs are thought to be linked to excep- tionally bright supernovae, while short GRBs likely result from neu- tron star collisions. Despite their in- tense brightness, these extragalactic sources are challenging to detect at the highest energies because the gamma rays they emit weaken over the vast distances they travel, as well as due to their transient nature. On 9 October 2022, space-based obser- vatories, such as NASA’s Fermi and Swift satellites, detected an ex- tremely bright long GRB, named GRB 221009A. “Dubbed the ‘BOAT’ (Brightest Of All Time), the burst was so intense that it saturated mul- tiple instruments observing it, and triggered follow-up observations across the globe,” explains Alicia López Oramas, researcher at the IAC and Publications Manager of LST Collaboration. “BOAT is a unique event: it is estimated that there will be one GRB per millennium with this intensity,” she adds. The LST-1 telescope, located at the CTAO’s northern array site in La Palma, began observing the event just 1.33 days after the initial explo- sion. Spanning over 20 days after the GRB onset, the observations with the LST-1 enabled the LST Col- laboration to identify an excess of gamma rays. “While this excess did A rtist’s impression of a gamma-ray burst. [ESO/A. Roquette]