SGR J1935+2154 has truly been the most prolific magnetar over the last decade: it has been entering into burst active episodes once every 1–2 yr since its discovery in 2014, it emitted the first Galactic fast radio burst associated with an X-ray burst in 2020, and it has emitted hundreds of energetic short bursts. Here, we present the time-resolved spectral analysis of 51 bright bursts from SGR J1935+2154. Unlike conventional time-resolved X-ray spectroscopic studies in the literature, we follow a two-step approach to probe true spectral evolution. For each burst, we first extract spectral information from overlapping time segments, fit them with three continuum models, and employ a machine-learning-based clustering algorithm to identify time segments that provide the largest spectral variations during each burst. We then extract spectra from those nonoverlapping (clustered) time segments and fit them again with the three models: the cutoff power-law model, the sum of two blackbody functions, and the model considering the emission of a modified blackbody undergoing resonant cyclotron scattering, which is applied systematically at this scale for the first time. Our novel technique allowed us to establish the genuine spectral evolution of magnetar bursts. We discuss the implications of our results and compare their collective behavior with the average burst properties of other magnetars.

中文翻译：

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磁星 SGR J1935+2154 爆发的简明谱时研究

SGR J1935+2154 确实是过去十年中最多产的磁星：自 2014 年被发现以来，它每 1-2 年就会进入一次爆发活跃期，它发射了第一个与 X 射线相关的银河快速射电爆发它在2020年爆发，并且已经发射了数百次高能短爆发。在这里，我们展示了 SGR J1935+2154 的 51 个明亮爆发的时间分辨光谱分析。与文献中传统的时间分辨 X 射线光谱研究不同，我们采用两步方法来探测真实的光谱演化。对于每个突发，我们首先从重叠的时间段中提取光谱信息，将它们与三个连续模型进行拟合，并采用基于机器学习的聚类算法来识别在每个突发期间提供最大光谱变化的时间段。然后，我们从那些不重叠（聚集）的时间段中提取光谱，并用三个模型再次拟合它们：截止幂律模型、两个黑体函数的总和以及考虑经过共振回旋散射的修改黑体发射的模型，如此规模的系统应用尚属首次。我们的新技术使我们能够确定磁星爆发的真正光谱演化。我们讨论了我们的结果的含义，并将它们的集体行为与其他磁星的平均爆发特性进行了比较。