# Detection of a spectral break in the extra hard component of GRB 090926A

Abstract : We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on board the \Fermi\ Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn suggests that there is a common region of emission across the entire \Fermi\ energy range. In addition, while a separate high-energy power-law component has already been observed in other GRBs, here we report for the first time the detection with good significance of a high-energy spectral break (or cutoff) in this power-law component around 1.4 GeV in the time-integrated spectrum. If the spectral break is caused by opacity to electron-positron pair production within the source, then this observation allows us to compute the bulk Lorentz factor for the outflow, rather than a lower limit.
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Article dans une revue
Astrophysical Journal, American Astronomical Society, 2011, 729, pp.114. 〈10.1088/0004-637X/729/2/114〉
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http://hal.in2p3.fr/in2p3-00587734
Contributeur : Virginie Mas <>
Soumis le : jeudi 21 avril 2011 - 13:09:27
Dernière modification le : jeudi 1 février 2018 - 01:39:28

### Citation

Markus Ackermann, Marco Ajello, K. Asano, M. Axelsson, Luca Baldini, et al.. Detection of a spectral break in the extra hard component of GRB 090926A. Astrophysical Journal, American Astronomical Society, 2011, 729, pp.114. 〈10.1088/0004-637X/729/2/114〉. 〈in2p3-00587734〉

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