The Peculiar Precursor of a Gamma-Ray Burst from a Binary Merger Involving a Magnetar
Shuo Xiao, Yan-Qiu Zhang, Zi-Pei Zhu, S. L. Xiong, H. Gao, D. Xu, Shuang‐Nan Zhang, Wen-Xi Peng, Xiao‐Bo Li, Peng Zhang, F. J. Lu, Lin Lın, Liang-Duan Liu, Zhen Zhang, M. Y. Ge, Y. L. Tuo, W. C. Xue, Shao-Yu Fu, Xing Liu, Jinzhong Liu, An Li, Tian-Cong Wang, Chao Zheng, Yue Wang, Shuai-Qing Jiang, Jin-Da Li, Jia-Cong Liu, Zhoujian Cao, Xi-Hong Luo, Jiaojiao Yang, Shu-Xu Yi, Xilu Wang, Ce Cai, Qi-Bin Yi, Yi Zhao, Sheng-Lun Xie, Cheng-Kui Li, Qi Luo, L. M. Song, Shuang‐Nan Zhang, Jin‐Lu Qu, Congzhan Liu, Xufang Li, Y. P. Xu, Ti-Pei Li
Abstract
Abstract The milestone discovery of GW170817-GRB 170817A-AT 2017gfo has shown that gravitational waves (GWs) could be produced during the merger of a neutron star–neutron star/black hole and that in electromagnetic (EM) waves, a gamma-ray burst (GRB) and a kilonova (KN) are generated in sequence after the merger. Observationally, however, EM properties before the merger phase are still unclear. Here we report a peculiar precursor in a KN-associated long-duration GRB 211211A, providing evidence of the EM before the merger. This precursor lasts ∼0.2 s, and the waiting time between the precursor and the main burst is ∼1 s, comparable to that between GW170817 and GRB 170817A. The spectrum of the precursor could be well fit with a nonthermal cutoff power-law model instead of a blackbody. In particular, a ∼22 Hz quasiperiodic oscillation candidate (∼3 σ ) is detected in the precursor. These temporal and spectral properties indicate that this precursor is probably produced by a catastrophic flare accompanied with magnetoelastic or crustal oscillations of a magnetar in a binary compact merger. The strong magnetic field of the magnetar can also account for the prolonged duration of GRB 211211A. However, it poses a challenge to reconcile the rather short lifetime of a magnetar with the rather long spiraling time of a binary neutron star system only by the GW radiation before the merger.