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arXiv · 1101.2082

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

Fermi-LAT·Fermi-GBM collaborations
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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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Fermi-LAT, Fermi-GBM collaborations. 2011-01-12. Detection of a spectral break in the extra hard component of GRB 090926A. https://doi.org/10.1088/0004-637x%2F729%2F2%2F114

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