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KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
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2011 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 729, no 2, nr 114- p.Article in journal (Refereed) Published
Abstract [en]

We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor 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 gamma-ray bursts, 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.

Place, publisher, year, edition, pages
2011. Vol. 729, no 2, nr 114- p.
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:kth:diva-32671DOI: 10.1088/0004-637X/729/2/114ISI: 000288608700037ScopusID: 2-s2.0-79952159931OAI: diva2:411363
Knut and Alice Wallenberg Foundation

QC 20110418

Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2014-08-20Bibliographically approved

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