LST Collaboration Sheds Light on Brightest Gamma-Ray Burst Ever Detected
La Palma, Spain — The international LST Collaboration, in which the Department of Nuclear and Particle Physics of UNIGE is involved (dans lequel le Département de physique nucléaire et corpusculaire de l’UNIGE est impliqué), has published significant findings on GRB 221009A, the most powerful gamma-ray burst (GRB) ever recorded. The results, featured in The Astrophysical Journal Letters (link to article), stem from observations conducted by the LST-1 telescope at the CTAO-North site in La Palma during its commissioning phase.
GRB 221009A, dubbed the “BOAT” (“Brightest Of All Time”), was detected in October 2022 by NASA’s Fermi and Swift satellites. LST-1 began follow-up observations just 1.33 days after the burst, collecting data over a 20-day period. While the observed gamma-ray excess did not meet the threshold for a formal detection, it enabled researchers to place strict limits on high-energy emission, offering new evidence for structured jet models in GRBs.
The data suggest a jet composed of a fast-moving core surrounded by a slower sheath, challenging simpler models used in earlier GRB studies. Notably, LST-1 achieved these observations under full moonlight—an operational first for the telescope—demonstrating new capabilities for observing transient cosmic events in difficult conditions.
These results mark a major step in the CTAO’s mission to explore the high-energy Universe and improve our understanding of extreme astrophysical phenomena.
23 Jul 2025