Yonetoku, Daisuke

Magnetic structure in relativistic jet of Gamma-Ray Bursts by the gamma-ray polarization with IKAROS-GAP.

Author list: Daisuke Yonetoku, Toshio Murakami, Shuichi Gunji, Tatehiro Mihara, Kenji Toma, Tomonori Sakashita, Yoshiyuki Morihara, Takuya Takahashi, Noriyuki Toukairin, Hirofumi Fujimoto, Yoshiki Kodama, Kanazawa University, Yamagata University, RIKEN, Osaka University

The Gamma-Ray Burst Polarimeter (GAP) aboard the solar sail IKAROS is the first polarimeter specifically designed to measure the gamma-ray polarization of prompt GRBs. We detected the polarization signals from three bright GRBs with almost above 3 sigma confidence level. For the case of GRB100826A, we also detected the firm change of polarization angle with 3.5 sigma confidence level. In view of gamma-ray polarization measurement, we consider that the magnetic fields may play an important role in the mechanism of prompt GRB. We suggest the non-axisymmetric (e.g. patchy) structures of the brightness and/or the magnetic fields inside the relativistic jet within the observable angular scale of Gamma^-1, to explain the observed significant change of polarization angle.