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The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks

Science  03 Jan 2014:
Vol. 343, Issue 6166, pp. 51-54
DOI: 10.1126/science.1242302

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Bright Lights

Gamma-ray bursts (GRBs), bright flashes of gamma-ray light, are thought to be associated with the collapse of massive stars. GRB 130427A was detected on 27 April 2013, and it had the longest gamma-ray duration and one of the largest isotropic energy releases observed to date (see the Perspective by Fynbo). Ackermann et al. (p. 42, published online 21 November) report data obtained with the Fermi Gamma-Ray Space Telescope, which reveal a high-energy spectral component that cannot be accounted for by the standard external shock synchrotron radiation model. Vestrand et al. (p. 38, published online 21 November) report the detection of an extremely bright flash of visible light and unexpected similarities between the variations of optical light and the highest-energy gamma rays that indicate a common origin. A detailed analysis of the first pulse of GRB 130427A by Preece et al. (p. 51, published online 21 November) suggests that existing models cannot explain all the observed spectral and temporal behaviors simultaneously. Maselli et al. (p. 48, published online 21 November) present x-ray and optical light curves of the burst's prompt emission as well as of its afterglow as recorded by the Swift satellite and a range of ground-based telescopes.

Abstract

Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 seconds is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.

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