AI 中文总结
本研究利用Swift/XRT 20年观测的427个带红移的X射线余辉样本，验证了GRB早期X射线光度与后续衰减速率的正相关性，发现该相关性仅存在于长暴中，且采样良好的长暴子样本相关性更强，为探究其成因提供了观测约束。
AI 中文摘要
伽马射线暴（GRB）余辉中的内禀光度-衰减相关性，即早期光度与该时刻之后的平均衰减速率之间的关联，此前已在射电、光学/紫外、X射线和GeV波段被观测到，且定量表明光度更高的余辉往往具有更高的平均衰减速率。我们汇编了一个更新的样本，包含427个具有已测量红移的X射线余辉，均由Swift/XRT在20年间观测得到。对于每个GRB，我们测量了静止系中200秒时的光度$L_{\text{X,200s}}$，以及从该时刻起的平均衰减速率$α_{X,>200s}$。我们发现这些参数存在相关性，斯皮尔曼等级相关系数（$R_\text{sp}$）为$0.54\boldsymbol{\boldsymbol{\boldsymbol{±}}}0.04$，显著性≥3σ，线性回归斜率为$0.18\boldsymbol{\boldsymbol{\boldsymbol{±}}}0.02$。我们将样本划分为多个子样本，包括395个长伽马射线暴（LGRBs）和32个短伽马射线暴（SGRBs），并发现在LGRBs中存在$L_{\text{X,200s}}$-$α_{X,>200s}$相关性的证据，显著性≥3σ，而在SGRBs中未发现该相关性，这与此前的研究结果一致。在一个包含102个光变曲线采样良好且终止时刻较晚的LGRBs子样本中，我们发现相关性的离散度显著降低，相关强度提升至$R_\text{sp}=0.80\boldsymbol{\boldsymbol{\boldsymbol{±}}}0.04$，而斜率与全样本保持一致。我们讨论了研究结果，并简要探讨了其对约束该相关性成因的潜在意义。可能的成因包括观测者与喷流轴之间夹角导致的几何效应，或是某种调控GRB中心引擎能量释放速率的机制。
英文摘要
The intrinsic luminosity-decay correlation in gamma-ray burst (GRB) afterglows, between the early-time luminosity and the average rate of decay past this time, has previously been observed in the radio, optical/UV, X-ray and GeV wavebands and quantitatively shows that more luminous afterglows tend to have higher average rates of decay. We have compiled an updated sample of 427 X-ray afterglows with measured redshifts, observed with Swift/XRT over 20 years. For each GRB, we measure the luminosity at 200 seconds in the rest frame, $L_{\mathrm{X,200s}}$, and the average rate of decay from this time, $α_{X,>200s}$. We find these parameters are correlated with a Spearman's rank coefficient ($R_\mathrm{sp}$) of $0.54\pm0.04$ at a significance of $\geq3σ$ and a linear regression slope of $0.18\pm0.02$. We separate our sample into subsamples, including 395 long GRBs (LGRBs) and 32 short GRBs (SGRBs) and find evidence of the $L_{\mathrm{X,200s}}$-$α_{X,>200s}$ correlation at a significance of $\geq3σ$ in LGRBs but not in SGRBs, consistent with previous studies. In a subsample of 102 LGRBs with well-sampled light curves and late end times, we find that scatter in the correlation is significantly reduced and the strength increases to $R_\mathrm{sp}=0.80\pm0.04$ whilst the slope remains consistent with the full sample. We discuss our results and, briefly, their potential implications on constraining the cause of the correlation. Possible causes include geometric effects due to the angle between the observer and the jet-axis, or some mechanism that regulates the rate at which energy is released by the GRB central engine.
Comments21 pages, 24 figures, accepted for publication in MNRAS
