Synchrotron Radiation Dominates the Extremely Bright GRB 221009A

Jun Yang; Xiao-Hong Zhao; Zhenyu Yan; Xiangyu I. Wang; Yan-Qiu Zhang; Zheng-Hua An; Ce Cai; Xin-Qiao Li; Zihan Li; Jia-Cong Liu; Zi-Ke Liu; Xiang Ma; Yan-Zhi Meng; Wen-Xi Peng; Rui Qiao; Lang Shao; Li-Ming Song; Wen-Jun Tan; Ping Wang; Chen-Wei Wang; Xiang-Yang Wen; Shuo Xiao; Wang-Chen Xue; Yu-han Yang; Yihan Yin; Bing Zhang; Fan Zhang; Shuai Zhang; Shuang-Nan Zhang; Chao Zheng; Shi-Jie Zheng; Shao-Lin Xiong; Bin-Bin Zhang

doi:10.3847/2041-8213/acc84b

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arXiv · 2303.00898

Synchrotron Radiation Dominates the Extremely Bright GRB 221009A

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Abstract

The brightest Gamma-ray burst, GRB 221009A, has spurred numerous theoretical investigations, with particular attention paid to the origins of ultra-high energy TeV photons during the prompt phase. However, analyzing the mechanism of radiation of photons in the $\sim$MeV range has been difficult because the high flux causes pile-up and saturation effects in most GRB detectors. In this letter, we present systematic modeling of the time-resolved spectra of the GRB using unsaturated data obtained from Fermi/GBM (precursor) and SATech-01/GECAM-C (main emission and flare). Our approach incorporates the synchrotron radiation model, which assumes an expanding emission region with relativistic speed and a global magnetic field that decays with radius, and successfully fits such a model to the observational data. Our results indicate that the spectra of the burst are fully in accordance with a synchrotron origin from relativistic electrons accelerated at a large emission radius. The lack of thermal emission in the prompt emission spectra supports a Poynting-flux-dominated jet composition.

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Jun Yang, Xiao-Hong Zhao, Zhenyu Yan, Xiangyu I. Wang, Yan-Qiu Zhang, Zheng-Hua An, Ce Cai, Xin-Qiao Li, Zihan Li, Jia-Cong Liu, Zi-Ke Liu, Xiang Ma, Yan-Zhi Meng, Wen-Xi Peng, Rui Qiao, Lang Shao, Li-Ming Song, Wen-Jun Tan, Ping Wang, Chen-Wei Wang, Xiang-Yang Wen, Shuo Xiao, Wang-Chen Xue, Yu-han Yang, Yihan Yin, Bing Zhang, Fan Zhang, Shuai Zhang, Shuang-Nan Zhang, Chao Zheng, Shi-Jie Zheng, Shao-Lin Xiong, Bin-Bin Zhang. 2023-03-02. Synchrotron Radiation Dominates the Extremely Bright GRB 221009A. https://doi.org/10.3847/2041-8213%2Facc84b

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