Fast radio bursts (FRBs) are bright, millisecond-scale radio flashes of unknown physical origin¹. Young, highly magnetized, isolated neutron stars—magnetars—have been suggested as the most promising candidates for FRB progenitors owing to their energetics and high X-ray flaring activity^2,3. Here we report the detection with Konus-Wind of a hard X-ray event of 28 April 2020 temporally coincident with a bright, two-peak radio burst^4,5 in the direction of Galactic magnetar SGR 1935+2154, with properties remarkably similar to those of FRBs. We show that the two peaks of the double-peaked X-ray burst coincide in time with the radio peaks and infer a common source and the association of these phenomena. An unusual hardness of the X-ray spectrum strongly distinguishes the 28 April event among multiple ‘ordinary’ flares from SGR 1935+2154. A recent non-detection^5,6,7 of radio emission from about 100 typical soft bursts from SGR 1935+2154 favours the idea that bright, FRB-like magnetar signals are associated with rare, hard-spectrum X-ray bursts. The implied rate of these hard X-ray bursts (~0.04 yr⁻¹ magnetar⁻¹) appears consistent with the rate estimate⁴ of SGR 1935+2154-like radio bursts (0.007–0.04 yr⁻¹ magnetar⁻¹).

快速射电暴 (FRB) 是未知物理来源的明亮的毫秒级射电闪光¹。年轻、高度磁化、孤立的中子星——磁星——由于其能量学和高 X 射线燃烧活动^2,3而被认为是 FRB 前身最有希望的候选者。在这里，我们报告了使用 Konus-Wind 检测到 2020 年 4 月 28 日的硬 X 射线事件，该事件与明亮的两个峰值射电暴^{4,5在时间上同时发生}在银河磁星 SGR 1935+2154 的方向上，其性质与快速射电暴非常相似。我们证明了双峰 X 射线爆发的两个峰在时间上与射电峰重合，并推断出一个共同的来源和这些现象的关联。X 射线光谱的异常硬度将 4 月 28 日的事件与 SGR 1935+2154 的多个“普通”耀斑区分开来。最近未检测到来自 SGR 1935+2154 的大约 100 个典型软爆发的无线电发射^5,6,7支持这样一种观点，即明亮的类似 FRB 的磁星信号与罕见的硬谱 X 射线爆发有关。这些硬 X 射线爆发的隐含速率（~0.04 年^-1 磁星^-1）似乎与速率估计一致⁴ SGR 1935+2154-like 射电暴（0.007–0.04 yr ^-1磁星-1）。