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arXiv · 1407.6430

The magnetization degree of the outflow powering the highly-polarized reverse shock emission of GRB 120308A

Shuai Zhang·Zhi-Ping Jin·Da-Ming Wei
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Abstract

GRB 120308A, a long duration $\gamma-$ray burst detected by {\it 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 reverse shock region is $\sim 10$ 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 $\sigma \sim$ a few percent. Considering the plausible magnetic energy dissipation in both the acceleration and prompt emission phases of the Gamma-ray Burst (GRB) outflow, the afterglow data of GRB 120308A provides us the compelling evidence that at least for some GRBs a non-ignorable fraction of the energy was released in the form of Poynting-flux, confirming the finding firstly made in the reverse-forward shock emission modeling of the optical afterglow of GRB 990123 (Fan et al. 2002; Zhang et al. 2003).

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Shuai Zhang, Zhi-Ping Jin, Da-Ming Wei. 2014-07-24. The magnetization degree of the outflow powering the highly-polarized reverse shock emission of GRB 120308A. https://doi.org/10.1088/0004-637x/798/1/3

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