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Observation of spectral lines in the exceptional GRB 221009A

Authors :
Zhang, Yan-Qiu
Xiong, Shao-Lin
Mao, Ji-Rong
Zhang, Shuang-Nan
Xue, Wang-Chen
Zheng, Chao
Liu, Jia-Cong
Zhang, Zhen
Wang, Xi-Lu
Ge, Ming-Yu
Yi, Shu-Xu
Song, Li-Ming
An, Zheng-Hua
Cai, Ce
Li, Xin-Qiao
Peng, Wen-Xi
Tan, Wen-Jun
Wang, Chen-Wei
Wen, Xiang-Yang
Wang, Yue
Xiao, Shuo
Zhang, Fan
Zhang, Peng
Zheng, Shi-Jie
Source :
Observation of spectral lines in the exceptional GRB 221009A. Sci. China-Phys. Mech. Astron. 67, 289511 (2024)
Publication Year :
2024

Abstract

As the brightest gamma-ray burst ever observed, GRB 221009A provided a precious opportunity to explore spectral line features. In this paper, we performed a comprehensive spectroscopy analysis of GRB 221009A jointly with GECAM-C and Fermi/GBM data to search for emission and absorption lines. For the first time we investigated the line feature throughout this GRB including the most bright part where many instruments suffered problems, and identified prominent emission lines in multiple time intervals. The central energy of the Gaussian emission line evolves from about 37 MeV to 6 MeV, with a nearly constant ratio (about 10\%) between the line width and central energy. Particularly, we find that both the central energy and the energy flux of the emission line evolve with time as a power law decay with power law index of -1 and -2 respectively. We suggest that the observed emission lines most likely originate from the blue-shifted electron positron pair annihilation 511 keV line. We find that a standard high latitude emission scenario cannot fully interpret the observation, thus we propose that the emission line comes from some dense clumps with electron positron pairs traveling together with the jet. In this scenario, we can use the emission line to directly, for the first time, measure the bulk Lorentz factor of the jet ($\Gamma$) and reveal its time evolution (i.e. $\Gamma \sim t^{-1}$) during the prompt emission. Interestingly, we find that the flux of the annihilation line in the co-moving frame keeps constant. These discoveries of the spectral line features shed new and important lights on the physics of GRB and relativistic jet.<br />Comment: Accepted by SCIENCE CHINA Physics, Mechanics & Astronomy (SCPMA)

Details

Database :
arXiv
Journal :
Observation of spectral lines in the exceptional GRB 221009A. Sci. China-Phys. Mech. Astron. 67, 289511 (2024)
Publication Type :
Report
Accession number :
edsarx.2403.12851
Document Type :
Working Paper
Full Text :
https://doi.org/10.1007/s11433-023-2381-0