GRB 221009A: the B.O.A.T Burst that Shines in Gamma Rays

• Published in: arXiv.org 2024-09
• Main Authors: Ajello, M, Arimoto, M, Baldini, L, Bellazzini, R, Berenji, B, Bissaldi, E, Bonino, R, Bruel, P, Cameron, R A, Caputo, R, Caraveo, P A, Cavazzuti, E, Cheung, C C, Chiaro, G, Cibrario, N, Ciprini, S, Cozzolongo, G, Orestano, P Cristarella, Crnogorcevic, M, Cutini, S, De Gaetano, S, N Di Lalla, Dinesh, A, L Di Venere, Domínguez, A, Fegan, S J, Ferrara, E C, Fiori, A, Funk, S, Fusco, P, Galanti, G, Gargano, F, Gasbarra, C, Germani, S, Giacchino, F, Giglietto, N, Giliberti, M, Gill, R, Giroletti, M, Granot, J, Green, D, Grenier, I A, Guiriec, S, Gustafsson, M, Hays, E, Hewitt, J W, Kayanoki, T, Kuss, M, Laviron, A, Loparco, F, Manfreda, A, Martí-Devesa, G, I Martinez Castellanos, Mazziotta, M N, Mereu, I, Mizuno, T, Monti-Guarnieri, P, Morishita, T, Morselli, A, Negro, M, Niwa, R, Omodei, N, Orienti, M, Orlando, E, Panzarini, G, Persic, M, Petrosian, V, Pillera, R, Piron, F, Racusin, J L, Rainò, S, Rando, R, Rani, B, Razzano, M, Razzaque, S, Reimer, O, Ryde, F, Serini, D, Sharma, V, Siskind, E J, Spandre, G, Suson, D J, Lesage, S, Briggs, M S, Burns, E, Cleveland, W H, Dalessi, S, de Barra, C, Gibby, M, Hristov, B A, Hui, C M, Kocevski, D, McBreen, S, Roberts, O J, Scotton, L, Veres, P, A von Kienlin, Wilson-Hodge, C A, Wood, J, Fermi GBM collaboration
• Format: Article
• Language: English
• Subjects: Afterglows; Emission; Gamma ray bursts; Gamma rays
• ISSN: 2331-8422

We present a complete analysis of Fermi Large Area Telescope (LAT) data of GRB 221009A, the brightest Gamma-Ray Burst (GRB) ever detected. The burst emission above 30 MeV detected by the LAT preceded by 1 s the low-energy (< 10 MeV) pulse that triggered the Fermi Gamma-Ray Burst Monitor (GBM), as has been observed in other GRBs. The prompt phase of GRB 221009A lasted a few hundred seconds. It was so bright that we identify a Bad Time Interval (BTI) of 64 seconds caused by the extremely high flux of hard X-rays and soft gamma rays, during which the event reconstruction efficiency was poor and the dead time fraction quite high. The late-time emission decayed as a power law, but the extrapolation of the late-time emission during the first 450 seconds suggests that the afterglow started during the prompt emission. We also found that high-energy events observed by the LAT are incompatible with synchrotron origin, and, during the prompt emission, are more likely related to an extra component identified as synchrotron self-Compton (SSC). A remarkable 400 GeV photon, detected by the LAT 33 ks after the GBM trigger and directionally consistent with the location of GRB 221009A, is hard to explain as a product of SSC or TeV electromagnetic cascades, and the process responsible for its origin is uncertain. Because of its proximity and energetic nature, GRB 221009A is an extremely rare event.