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Title: THE MAGNETIZATION DEGREE OF THE OUTFLOW POWERING THE HIGHLY POLARIZED REVERSE-SHOCK EMISSION OF GRB 120308A

GRB 120308A, a long duration γ-ray burst (GRB) detected by Swift, was distinguished by a highly polarized early optical afterglow emission that strongly suggests an ordered magnetic field component in the emitting region. In this work, we model the optical and X-ray emission in the reverse and forward shock scenario and show that the strength of the magnetic field in the reverse-shock region is ∼10 times stronger than that in the forward shock region. Consequently, the outflow powering the highly polarized reverse-shock optical emission was mildly magnetized at a degree of σ ∼ a few percent. Considering the plausible magnetic energy dissipation in both the acceleration and prompt emission phases of the GRB outflow, the afterglow data of GRB 120308A provides us with compelling evidence that, at least for some GRBs, a nonignorable fraction of the energy was released in the form of Poynting flux, confirming the finding first made in the reverse-forward shock emission modeling of the optical afterglow of GRB 990123 by Fan et al. in 2002 and Zhang et al. in 2003.
Authors:
; ;  [1]
  1. Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210008 (China)
Publication Date:
OSTI Identifier:
22364782
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 798; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; AFTERGLOW; BLOWERS; COMPUTERIZED SIMULATION; COSMIC GAMMA BURSTS; ENERGY LOSSES; GAMMA RADIATION; MAGNETIC FIELDS; MAGNETIZATION; PHOTON EMISSION; X RADIATION