GRB 210121A: A Typical Fireball Burst Detected by Two Small Missions
X. Wang, Xutao Zheng, Shuo Xiao, Jun Yang, Zi-Ke Liu, Yu-Han Yang, Jin-Hang Zou, Bin‐Bin Zhang, M. Zeng, S. L. Xiong, Hua Feng, X. Y. Song, Jiaxing Wen, D. Xu, Guoyin Chen, Yang Ni, Zijian Zhang, Yuxuan Wu, Ce Cai, Jirong Cang, Yunwei Deng, Huaizhong Gao, Defeng Kong, Y. Huang, Cheng-Kui Li, Hong Li, Xiao‐Bo Li, En‐Wei Liang, Lin Lın, Yihui Liu, Xiangyun Long, Dian Lu, Q. Luo, Y. Ma, Yan-Zhi Meng, Wen-Xi Peng, Rui Qiao, L. M. Song, Yang Tian, Peiyuan Wang, Ping Wang, Xiang-Gao Wang, Sheng Xu, Dongxin Yang, Yi-Han Iris Yin, Weihe Zeng, Zhi Zeng, Tingjun Zhang, Yuchong Zhang, Zhao Zhang, Zhen Zhang
Abstract
Abstract The Chinese CubeSat Mission, Gamma Ray Integrated Detectors (GRID), recently detected its first gamma-ray burst, GRB 210121A, which was jointly observed by the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM). This burst is confirmed by several other missions, including Fermi and Insight-HXMT. We combined multimission observational data and performed a comprehensive analysis of the burst’s temporal and spectral properties. Our results show that the burst is relatively special in its high peak energy, thermal-like low-energy indices, and large fluence. By putting it to the E p – E γ ,iso relation diagram with assumed distance, we found that this burst can be constrained at the redshift range of [0.3, 3.0]. The thermal spectral component is also confirmed by the direct fit of the physical models to the observed spectra. Interestingly, the physical photosphere model also constrained a redshift of z ∼ 0.3 for this burst, which helps us to identify a host galaxy candidate at such a distance within the location error box. Assuming that the host galaxy is real, we found that the burst can be best explained by the photosphere emission of a typical fireball with an initial radius of r 0 ∼ 3.2 × 10 7 cm.