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

Axelsson M.; Ajello M.; Arimoto M.; Baldini L.; Ballet J.; Baring M. G.; Bartolini C.; Bastieri D.; Becerra Gonzalez J.; Bellazzini R.; Berenji B.; Bissaldi E.; Blandford R. D.; Bonino R.; Bruel P.; Buson S.; Cameron R. A.; Caputo R.; Caraveo P. A.; Cavazzuti E.; Cheung C. C.; Chiaro G.; Cibrario N.; Ciprini S.; Cozzolongo G.; Cristarella Orestano P.; Crnogorcevic M.; Cuoco A.; Cutini S.; D'Ammando F.; De Gaetano S.; Di Lalla N.; Dinesh A.; Di Tria R.; Di Venere L.; Dominguez A.; Fegan S. J.; Ferrara E. C.; Fiori A.; Franckowiak A.; Fukazawa Y.; Funk S.; Fusco P.; Galanti G.; Gargano F.; Gasbarra C.; Germani S.; Giacchino F.; Giglietto N.; Giliberti M.; Gill R.; Giordano F.; Giroletti M.; Granot J.; Green D.; Grenier I. A.; Guiriec S.; Gustafsson M.; Hashizume M.; Hays E.; Hewitt J. W.; Horan D.; Kayanoki T.; Kuss M.; Laviron A.; Li J.; Liodakis I.; Longo F.; Loparco F.; Lorusso L.; Lott B.; Lovellette M. N.; Lubrano P.; Maldera S.; Malyshev D.; Manfreda A.; Marti-Devesa G.; Martinelli R.; Martinez Castellanos I.; Mazziotta M. N.; McEnery J. E.; Mereu I.; Meyer M.; Michelson P. F.; Mirabal N.; Mitthumsiri W.; Mizuno T.; Monti-Guarnieri P.; Monzani M. E.; Morishita T.; Morselli A.; Moskalenko I. V.; Negro M.; Niwa R.; Omodei N.; Orienti M.; Orlando E.; Paneque D.; Panzarini G.; Persic M.; Pesce-Rollins M.; Petrosian V.; Pillera R.; Piron F.; Porter T. A.; Principe G.; Racusin J. L.; Raino S.; Rando R.; Rani B.; Razzano M.; Razzaque S.; Reimer A.; Reimer O.; Ryde F.; Sanchez-Conde M.; Saz Parkinson P. M.; Serini D.; Sgro C.; Sharma V.; Siskind E. J.; Spandre G.; Spinelli P.; Suson D. J.; Tajima H.; Tak D.; Thayer J. B.; Torres D. F.; Valverde J.; Zaharijas G.; Lesage S.; Briggs M. S.; Burns E.; Bala S.; Bhat P. N.; Cleveland W. H.; Dalessi S.; de Barra C.; Gibby M.; Giles M. M.; Hamburg R.; Hristov B. A.; Kocevski D.; Hui C. M.; Mailyan B.; Malacaria C.; McBreen S.; Poolakkil S.; Roberts O. J.; Scotton L.; Veres P.; von Kienlin A.; Wilson-Hodge C. A.; Wood J.

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

Axelsson M.

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Ajello M.

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Arimoto M.

altro

Wood J.

2025

journal article

Periodico

ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES

Abstract

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 of 64 s 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 s 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.