利用X射线余辉中的喷流拐折特征限制伽马射线暴（GRB）的暴周环境
Constraining Circum-burst Environments of GRBs with Jet Break Features in X-ray Afterglows
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中文总结 AI 辅助
本研究利用170个带清晰喷流拐折的GRB样本，通过X射线余辉的Δα推导密度轮廓指数k，分类其暴周环境，发现近半数为星际介质、半数为星风环境，且与多波段分析结果一致，还推导了部分暴的喷流参数。
中文摘要 AI 辅助
暴周介质的性质是探究伽马射线暴（GRB）前身系统及相对论性喷流传播物理的关键诊断依据。本研究从喷流拐折处的时变衰减指数变化量Δα出发，系统推断密度轮廓指数k（满足n∝r⁻ᵏ）；在均匀喷流模型框架下，二者满足关系Δα=(3−k)/(4−k)。我们将该诊断方法应用于从2004年至2024年观测的1400余个Swift/XRT X射线余辉中识别出的、经均匀筛选的170个具有清晰喷流拐折的GRB样本，通过折断幂律模型拟合光变曲线，得到每个暴的Δα并推导对应k值，进而用推导的k值对每个GRB的暴周环境分类。结果显示近半数分布：82个暴（约48%）符合恒定密度星际介质（ISM，k≈0），88个暴（约52%）支持星风环境（k≈2）；对35个有光学数据的暴，我们基于X射线的分类与独立多波段分析总体一致。此外，我们对已知红移的暴推导了喷流张角及经波束校正的真实能量。
英文摘要
The nature of the circum-burst medium serves as a key diagnostic for probing the progenitor systems and the physics of relativistic jet propagation in gamma-ray bursts (GRBs). In this work, we systematically infer the density profile index $k$ (where $n \propto r^{-k}$) from the change in the temporal decay index at the jet break ($Δα$). Within the framework of the uniform jet model, the two quantities are linked by the relation $Δα= (3 - k)/(4 - k)$. We apply this diagnostic to a substantial and uniformly selected sample of 170 GRBs with clear jet breaks, identified from over 1,400 Swift/XRT X-ray afterglows observed from 2004 to 2024. By fitting the light curves with a broken power-law model, we obtain $Δα$ for each burst and subsequently derive the corresponding $k$ value. We then use the derived $k$ values to classify the circum-burst environment of each GRB. Our results reveal a near-even split: 82 bursts ($\sim48\%$) are consistent with a constant-density interstellar medium (ISM, $k \approx 0$), while 88 bursts ($\sim52\%$) favor a wind environment ($k \approx 2$). For the 35 bursts with optical data, our X-ray-based classifications are generally consistent with independent multi-band analyses. Additionally, we derive jet opening angles and true beaming-corrected energies for bursts with known redshifts.
