Detection of Gamma-Ray polarization in prompt emission of GRB 100826A

Daisuke Yonetoku, Toshio Murakami, Shuichi Gunji, Tatehiro Mihara, Kenji Toma, Tomonori Sakashita, Yoshiyuki Morihara, Takuya Takahashi, Noriyuki Toukairin, Hirofumi Fujimoto, Yoshiki Kodama, Shin Kubo, Demonstration Team Ikaros Demonstration Team

Research output: Contribution to journalArticlepeer-review

121 Citations (Scopus)

Abstract

We report the polarization measurement in prompt γ-ray emission of GRB 100826A with the Gamma-Ray Burst Polarimeter on board the small solar-power-sail demonstrator IKAROS. We detected the firm change of polarization angle (PA) during the prompt emission with 99.9% (3.5σ) confidence level, and the average polarization degree (Π) of 27% 11% with 99.4% (2.9σ) confidence level. Here the quoted errors are given at 1σ confidence level for the two parameters of interest. The systematic errors have been carefully included in this analysis, unlike other previous reports. Such a high Π can be obtained in several emission models of gamma-ray bursts (GRBs), including synchrotron and photospheric models. However, it is difficult to explain the observed significant change of PA within the framework of axisymmetric jet as considered in many theoretical works. The non-axisymmetric (e.g., patchy) structures of the magnetic fields and/or brightness inside the relativistic jet are therefore required within the observable angular scale of Γ-1. Our observation strongly indicates that the polarization measurement is a powerful tool to constrain the GRB production mechanism, and more theoretical works are needed to discuss the data in more detail.

Original languageEnglish
Article numberL30
JournalAstrophysical Journal Letters
Volume743
Issue number2
DOIs
Publication statusPublished - 2011 Dec 20
Externally publishedYes

Keywords

  • gamma-ray burst: individual (GRB 100826A)
  • instrumentation: polarimeters
  • polarization
  • radiation mechanisms: non-thermal
  • relativistic processes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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