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基于Amati关系对长暴观测角的限制

Limitation on the Viewing Angles of Long GRBs Based on Amati Relation

  • 摘要: 从1997年2月至2023年9月期间具有已知红移和良好能谱参数的323个长暴样本中, 选取其中123个由Fermi伽马暴探测器(Fermi Gamma-Ray Burst Monitor, Fermi-GBM)观测的样本重新拟合了各向同性能量E_\rmiso与静止系峰值能量E_\rmp,i之间的关系(Amati关系). 结果显示: 5个暴(GRB 980425、GRB 061210、GRB 070714B、GRB 071227、GRB 080123A)的E_\rmiso和E_\rmp,i散点偏离Amati关系最远, 表明其观测的视线方向最有可能偏离喷流轴. 基于E_\rmiso-E_\rmp,i关系以及洛伦兹因子\varGamma与E_\rmiso之间的关系(\varGamma-E_\rmiso), 估算这5个暴的观测视线与喷流边缘的夹角\theta_\rmobs^'. 结果分别为GRB 980425的\theta^'_\rmobs=(0.42^+0.29_-0.14)^\circ、GRB 061210的\theta^'_\rmobs=(0.27^+0.21_-0.10)^\circ、GRB 070714B的\theta^'_\rmobs=(0.10^+0.09_-0.02)^\circ、GRB 071227的\theta^'_\rmobs=(0.13^+0.09_-0.05)^\circ、GRB 080123A的\theta^'_\rmobs=(0.12^+0.14_-0.03)^\circ. 结果显示5个\theta_\rmobs^'都很小, 最大的是目前观测到的离我们最近的长暴GRB 980425 (红移为z=0.0085), \theta_\rmobs^'为0.42^\circ。这意味着大部分长暴可能是正轴观测, 仅有少数临近暴的观测视线稍微偏离喷流边缘线.

     

    Abstract: Fermi, Swift, and other observation satellites provided a dataset of 323 Long Gamma-Ray Bursts (LGRBs) with known redshift and well-defined spectral parameters spanning from February 1997 to September 2023. Among these, 123 GRBs (Gamma-Ray Bursts) observed by Fermi-GBM were selected to calibrate the relationship between the isotropic energy E_\rmiso and the peak energy in the cosmological rest frame E_\rmp,i, known as the Amati relation. The analysis revealed that the E_\rmiso of five LGRBs (GRB 980425, GRB 061210, GRB 070714B, GRB 071227, and GRB 080123A) significantly deviated from the Amati relation, suggesting that the jet of them may be off-axis to the line of sight. Utilizing the well-established E_\rmp,i-\varGamma and E_\rmp,i-E_\rmiso correlations, we estimated the viewing angles \theta _\rmobs^' for these five LGRBs. The results show, \theta^'_\rmobs=(0.42^+0.29_-0.14)^\circ for GRB 980425, \theta^'_\rmobs=(0.27^+0.21_-0.10)^\circ for GRB 061210, \theta^'_\rmobs=(0.10^+0.09_-0.02)^\circ for GRB 070714B, \theta^'_\rmobs=(0.13^+0.09_-0.05)^\circ for GRB 071227, and \theta^'_\rmobs=(0.12^+0.14_-0.03)^\circ for GRB 080123A. Notably, all five \theta _\rmobs^' values are small, with the maximum angle being 0.42^\circ for GRB 980425, the nearest long burst observed (z=0.0085). The results suggest that the majority of Long GRBs are likely detected on-axis, with only a small fraction of nearby Long GRBs being observed slightly outside the jet edge.

     

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