The late peaking afterglow of GRB 100418A

F. E. Marshall, L. A. Antonelli, D. N. Burrows, S. Covino, M. De Pasquale, P. A. Evans, D. Fugazza, S. T. Holland, E. W. Liang, P. T. O'Brien, S. R. Oates, J. P. Osborne, C. Pagani, T. Sakamoto, M. H. Siegel, X. F. Wu, B. Zhang

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GRB 100418A is a long gamma-ray burst (GRB) at redshift z = 0.6235 discovered with the Swift Gamma-ray Burst Explorer with unusual optical and X-ray light curves. After an initial short-lived, rapid decline in X-rays, the optical and X-ray light curves observed with Swift are approximately flat or rising slightly out to at least ∼7 × 103 s after the trigger, peak at ∼5 × 104 s, and then follow an approximately power-law decay. Such a long optical plateau and late peaking is rarely seen in GRB afterglows. Observations with Rapid Eye Mount during a gap in the Swift coverage indicate a bright optical flare at ∼2.5 × 10 4 s. The long plateau phase of the afterglow is interpreted using either a model with continuous injection of energy into the forward shock of the burst or a model in which the jet of the burst is viewed off-axis. In both models the isotropic kinetic energy in the late afterglow after the plateau phase is ≥102 times the 1051 erg of the prompt isotropic gamma-ray energy release. The energy injection model is favored because the off-axis jet model would require the intrinsic T90 for the GRB jet viewed on-axis to be very short, ∼10 ms, and the intrinsic isotropic gamma-ray energy release and the true jet energy to be much higher than the typical values of known short GRBs. The non-detection of a jet break up to t ∼ 2 × 106 s indicates a jet half-opening angle of at least ∼14°, and a relatively high-collimation-corrected jet energy of Ejet ≥ 1052 erg.

Original languageEnglish (US)
JournalAstrophysical Journal
Issue number2
StatePublished - Feb 1 2011

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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