Paper

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

Morselli, A, Maldera, S, Mazziotta, M N, Thayer, J B, Fermi LAT collaboration, Dalessi, S, Kuss, M, Cutini, S, J Li, Buson, S, Giacchino, F, Hristov, B A, Hamburg, R, Martí-Devesa, G, Monti-Guarnieri, P, Negro, M, Fusco, P, Orestano, P Cristarella, Funk, S, Racusin, J L, Roberts, O J, Gasbarra, C, Valverde, J, Laviron, A, Zaharijas, G, Crnogorcevic, M, De Gaetano, S, Lorusso, L, Moskalenko, I V, Sharma, V, Gill, R, Poolakkil, S, Orlando, E, Mailyan, B, Manfreda, A, Torres, D F, Briggs, M S, Razzaque, S, Tajima, H, Cozzolongo, G, Caraveo, P A, Rani, B, Bissaldi, E, A von Kienlin, Saz Parkinson, P M, Fegan, S J, de Barra, C, Lott, B, Cuoco, A, R Di Tria, Niwa, R, Hui, C M, Hashizume, M, Baring, M G, Granot, J, Hays, E, Monzani, M E, Persic, M, Longo, F, Spandre, G, Loparco, F, Gargano, F, L Di Venere, Panzarini, G, Chiaro, G, Dinesh, A, McEnery, J E, Siskind, E J, Bellazzini, R, Galanti, G, Kocevski, D, Principe, G, Cleveland, W H, Cavazzuti, E, Burns, E, Horan, D, Giroletti, M, Razzano, M, Sgrò, C, Kayanoki, T, Bruel, P, Spinelli, P, Veres, P, Lesage, S, J Becerra Gonzalez, Berenji, B, Fukazawa, Y, Martinelli, R, Rando, R, Germani, S, Giles, M M, Ferrara, E C, Green,

2024

Overview

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.

• Publisher: Cornell University Library, arXiv.org
• Subject: Afterglows / Emission / Gamma ray bursts / Gamma rays