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Title: The ultraluminous GRB 110918A

GRB 110918A is the brightest long gamma-ray burst (GRB) detected by Konus-WIND during its almost 19 yr of continuous observations and the most luminous GRB ever observed since the beginning of the cosmological era in 1997. We report on the final Interplanetary Network localization of this event and its detailed multiwavelength study with a number of space-based instruments. The prompt emission is characterized by a typical duration, a moderate peak energy of the time-integrated spectrum, and strong hard-to-soft evolution. The high observed energy fluence yields, at z = 0.984, a huge isotropic-equivalent energy release E {sub iso} = (2.1 ± 0.1) × 10{sup 54} erg. The record-breaking energy flux observed at the peak of the short, bright, hard initial pulse results in an unprecedented isotropic-equivalent luminosity L {sub iso} = (4.7 ± 0.2) × 10{sup 54} erg s{sup –1}. A tail of the soft γ-ray emission was detected with temporal and spectral behavior typical of that predicted by the synchrotron forward-shock model. The Swift/X-Ray Telescope and the Swift/Ultraviolet Optical Telescope observed the bright afterglow from 1.2 to 48 days after the burst and revealed no evidence of a jet break. The post-break scenario for the afterglow is preferred from ourmore » analysis, with a hard underlying electron spectrum and interstellar-medium-like circumburst environment implied. We conclude that, among the multiple reasons investigated, the tight collimation of the jet must have been a key ingredient to produce this unusually bright burst. The inferred jet opening angle of 1.°7-3.°4 results in reasonable values of the collimation-corrected radiated energy and the peak luminosity, which, however, are still at the top of their distributions for such tightly collimated events. We estimate a detection horizon for a similar ultraluminous GRB of z ∼ 7.5 for Konus-WIND and z ∼ 12 for the Swift/Burst Alert Telescope, which stresses the importance of GRBs as probes of the early Universe.« less
Authors:
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  1. Ioffe Physical-Technical Institute, Politekhnicheskaya 26, St. Petersburg 194021 (Russian Federation)
  2. Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720-7450 (United States)
  3. Pennsylvania State University, Department of Astronomy and Astrophysics, College Park, PA 16801 (United States)
  4. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom)
  5. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  6. University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)
  7. Space Research Institute, Profsoyuznaya 84/32, Moscow 117997 (Russian Federation)
Publication Date:
OSTI Identifier:
22348428
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AFTERGLOW; COSMIC GAMMA BURSTS; DETECTION; DISTRIBUTION; ELECTRON SPECTRA; EMISSION; EVOLUTION; LUMINOSITY; PULSES; SPACE; SYNCHROTRONS; TELESCOPES; ULTRAVIOLET RADIATION; UNIVERSE; X RADIATION