Magnetars are young, magnetically powered neutron stars that possess the strongest magnetic fields in the Universe. Fast radio bursts (FRBs) are extremely intense millisecond-long radio pulses of primarily extragalactic origin, and a leading attribution for their genesis focuses on magnetars. A hallmark signature of magnetars is their emission of bright, hard X-ray bursts of sub-second duration. On 27 April 2020, the Galactic magnetar SGR J1935+2154 emitted hundreds of X-ray bursts within a few hours. One of these temporally coincided with an FRB, the first known detection of an FRB from the Milky Way. Here, we present spectral and temporal analyses of 24 X-ray bursts emitted 13 hours prior to the FRB and seen simultaneously with the Neutron Star Interior Composition Explorer (NICER) mission of the National Aeronautics and Space Administration and with the Fermi Gamma-ray Burst Monitor (GBM) mission in their combined energy range of 0.2 keV to 30 MeV. These broadband spectra permit direct comparison with the spectrum of the FRB-associated X-ray burst (FRB-X). We demonstrate that all 24 NICER and GBM bursts are very similar temporally to the FRB-X, but strikingly different spectrally. The singularity of the FRB-X burst is perhaps indicative of an uncommon locale for its origin. We suggest that this event originated in quasi-polar open or closed magnetic field lines that extend to high altitudes.

磁星是年轻的、磁力驱动的中子星，拥有宇宙中最强的磁场。快速射电暴 (FRB) 是极其强烈的毫秒长射电脉冲，主要起源于河外，其起源的主要归因于磁星。磁星的一个标志性特征是它们发射亚秒级持续时间的明亮、硬 X 射线爆发。2020 年 4 月 27 日，银河磁星 SGR J1935+2154 在几个小时内发射了数百次 X 射线爆发。其中一个在时间上与快速射电暴同时发生，这是已知的第一次从银河系中检测到快速射电暴。这里，我们展示了在 FRB 之前 13 小时发射的 24 次 X 射线爆发的光谱和时间分析，这些 X 射线爆发与美国国家航空航天局的中子星内部成分探测器 (NICER) 任务和费米伽马射线爆发监测器同时观察到。 GBM) 任务的综合能量范围为 0.2 keV 至 30 MeV。这些宽带光谱允许与 FRB 相关 X 射线爆发 (FRB-X) 的光谱进行直接比较。我们证明所有 24 个 NICER 和 GBM 爆发在时间上与 FRB-X 非常相似，但在光谱上却截然不同。FRB-X 爆发的奇点可能表明其起源的一个不常见的地点。我们认为这一事件起源于延伸到高海拔的准极性开放或封闭磁场线。