标题： GRB瞬时数据的极值分布——BOAT事件有多意外？ 显示英文标题

标题： Extreme value distribution for GRB prompt data -- How unexpected was the BOAT event?

摘要： 伽马射线暴（GRBs）在时间和位置上被认为是不可预测的。 一些（观测上）特殊的事件已被观测到，如GRB221009A，它因其通量和峰值流量而突出，比迄今为止测量的高出几个数量级。 分析观测到的通量、峰值流量或持续时间分布通常需要假设某些情景，观测数据与预测的一致性被证明是重要的模型诊断。 然而，使用不依赖于特定模型假设的通用统计特性来建模这些分布也具有重要意义，这使得仅基于观测分布与生成它们的单一事件种群假设的一致性来得出推论成为可能。 我们从CGRO-BATSE和Fermi-GBM仪器观测到的伽马射线暴目录中获得了通量、峰值流量和持续时间。 我们在等长的时间段内选择了极端值，并用广义极值（GEV）形式来模拟它们的分布。 GEV分布是在观测数量较大时自然出现的极限分布，基本上与产生观测数据的现象无关。 通量、峰值流量和持续时间的极端值分布与从单一事件种群中提取的分布一致，但GRB221009A记录的通量和峰值流量构成一个显著的例外。 假设这是一个宇宙学伽马射线暴，观察到这种事件的概率较低，通量的中位数约为每千年一次，峰值流量约为每世纪一次。 显示英文摘要

摘要： Gamma-Ray Bursts (GRBs) are known to be unpredictable in time and position. A few (observationally) exceptional events have been observed, as GRB221009A that stands out for its fluence and peak flux, being orders of magnitude higher than what measured so far. Analyzing the observed fluence, peak flux or duration distributions typically requires one to assume some scenarios, and the consistency of the observed data with the predictions turns out to be an important model diagnostic. However, it is also of interest to model these distributions using general statistical properties that do not rely on specific model assumptions, allowing one to derive inferences only based on the consistency of the observed distributions with the hypothesis of one single population of events that generate them. We obtained fluences, peak fluxes and durations from the catalogues of GRBs observed by the CGRO-BATSE and Fermi-GBM instruments. We selected the extreme values in slots of equal duration and modelled their distributions by the generalized extreme value (GEV) formalism. The GEV distribution is a limit distribution naturally arising when the number of observations is large and is essentially independent of the phenomena producing the observed data. The distributions of extreme values for fluences, peak fluxes and durations are consistent with being extracted from a single population of events but the fluence and peak flux recorded for GRB221009A constitutes a striking exception. The probability to observe such an event, assuming it is a cosmological GRB, is low, with a median value of about one event per millennium for the fluence and about one event per century for the peak flux.