Study of emission mechanism of Gamma-Ray Bursts by the gamma-ray polarization with IKAROS-GAP

Daisuke Yonetoku, Toshio Murakami, Shuichi Gunji, Tatehiro Mihara, Kenji Toma

Research output: Contribution to journalConference articlepeer-review


We report the polarization measurement in prompt γ -ray emission of GRB 100826A, GRB 110301A and GRB 110721A with the Gamma-Ray Burst Polarimeter (GAP) aboard the small solar power sail demonstrator IKAROS. We detected the firm change of polarization angle (PA) during the prompt emission of GRB 100826A with 99.9 % (3.5 σ ) confidence level, and the average polarization degree (Π) of 27 ± 11 % with 99.4 % (2.9 σ ) confidence level. For the later two events, we detected the strong polarization of Π = 70 ± 22 % and Π = 84+ 16 28 % with the statistical significance of 3.7 σ and 3.3 σ , respectively. Here the quoted errors are given at 1 σ confidence level for two parameters of interest. We conclude the linear gamma-ray polarization exists in the prompt GRBs from GAP observations. 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 - 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 details.

Original languageEnglish
JournalProceedings of Science
Publication statusPublished - 2012 Jan 1
Externally publishedYes
Event2012 Gamma-Ray Bursts Conference, GRB 2012 - Munich, Germany
Duration: 2012 May 72012 May 11

ASJC Scopus subject areas

  • General


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