Gamma-ray bursts (GRBs) are highly variable and exhibit strong spectral evolution. In particular, the emission properties vary from pulse to pulse in multipulse bursts. Here we present a time-resolved Bayesian spectral analysis of a compilation of GRB pulses observed by the Fermi/Gamma-ray Burst Monitor. The pulses are selected to have at least four time bins with a high statistical significance, which ensures that the spectral fits are well determined and spectral correlations can be established. The sample consists of 39 bursts, 117 pulses, and 1228 spectra. We confirm the general trend that pulses become softer over time, with mainly the low-energy power-law index α becoming smaller. A few exceptions to this trend exist, with the hardest pulse occurring at late times. The first pulse in a burst is clearly different from the later pulses; three-fourths of them violate the synchrotron line of death, while around half of them significantly prefer photospheric emission. These fractions decrease for subsequent pulses. We also find that in two-thirds of the pulses, the spectral parameters (α and peak energy) track the light-curve variations. This is a larger fraction compared to what is found in previous samples. In conclusion, emission compatible with the GRB photosphere is typically found close to the trigger time, while the chance of detecting synchrotron emission is greatest at late times. This allows for the coexistence of emission mechanisms at late times.

伽马射线暴 (GRB) 是高度可变的，并且表现出强烈的光谱演化。特别是，发射特性在多脉冲猝发中因脉冲而异。在这里，我们展示了费米/伽玛射线暴监测器观测到的 GRB 脉冲汇编的时间分辨贝叶斯光谱分析。脉冲被选择为具有至少四个具有高统计显着性的时间段，这确保光谱拟合被很好地确定并且可以建立光谱相关性。样本由 39 个突发、117 个脉冲和 1228 个光谱组成。我们确认了脉冲随时间变软的总体趋势，主要是低能量幂律指数α变得更小。这种趋势存在一些例外，最困难的脉冲发生在后期。突发中的第一个脉冲与后面的脉冲明显不同；其中四分之三违反了同步加速器死亡线，而其中大约一半的人明显更喜欢光球发射。对于随后的脉冲，这些分数减少。我们还发现，在三分之二的脉冲中，光谱参数（α和峰值能量）跟踪光曲线变化。与之前样本中发现的相比，这是一个更大的比例。总之，与 GRB 光球层兼容的发射通常在触发时间附近发现，而在后期检测同步加速器发射的机会最大。这允许发射机制在后期共存。