The Astrophysical Journal Letters (Jan 2023)

Synchrotron Radiation Dominates the Extremely Bright GRB 221009A

  • Jun Yang,
  • Xiao-Hong Zhao,
  • Zhenyu Yan,
  • Xiangyu Ivy 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,
  • Yi-Han Iris Yin,
  • Bing Zhang,
  • Fan Zhang,
  • Shuai Zhang,
  • Shuang-Nan Zhang,
  • Chao Zheng,
  • Shi-Jie Zheng,
  • Shao-Lin Xiong,
  • Bin-Bin Zhang

DOI
https://doi.org/10.3847/2041-8213/acc84b
Journal volume & issue
Vol. 947, no. 1
p. L11

Abstract

Read online

The brightest gamma-ray burst, GRB 221009A, has spurred numerous theoretical investigations, with particular attention paid to the origins of ultrahigh-energy TeV photons during the prompt phase. However, analyzing the mechanism of radiation of photons in the ∼MeV range has been difficult because the high flux causes pileup 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 the Fermi Gamma-ray Burst Monitor (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.

Keywords