Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2011-01-11
Astrophys.J.729:114,2011
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
31 pages, 6 figures, accepted by ApJ for publication Contact Authors: Johan Bregeon (johan.bregeon@pi.infn.it), Adam Goldstein
Scientific paper
10.1088/0004-637X/729/2/114
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.
collaborations Fermi-GBM
Fermi-LAT
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