ABSTRACT

The jet structure of short gamma-ray bursts (GRBs) has been controversial after the detection of GRB 170817A as the electromagnetic counterparts to the gravitational wave event GW170817. Different authors use different jet structures for calculating the afterglow light curves. We formulated a method to inversely reconstruct a jet structure from a given off-axis GRB afterglow, without assuming any functional form of the structure. By systematically applying our inversion method, we find that more diverse jet structures are consistent with the observed afterglow of GRB 170817A within errors such as hollow-cone, spindle, Gaussian, and power-law jet structures. In addition, the total energy of the reconstructed jet is arbitrary, proportional to the ambient density (n₀), with keeping the same jet shape if the parameters satisfy the degeneracy combination $n_0 \varepsilon _\mathrm{B}^{(p+1)/(p+5)} \varepsilon _\mathrm{e}^{4(p-1)/(p+5)} = \mathrm{const.}$ Observational accuracy less than ∼6 per cent is necessary to distinguish the different shapes, while the degeneracy of the energy scaling would be broken by observing the spectral breaks and viewing angle. Future events in denser environment with brighter afterglows and observable spectral breaks are ideal for our inversion method to pin down the jet structure, providing the key to the jet formation and propagation.

中文翻译：

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多种射流结构与GRB 170817A的离轴余辉一致

摘要

在检测到GRB 170817A作为重力波事件GW170817的电磁对应物之后，短伽马射线暴（GRB）的射流结构引起了争议。不同的作者使用不同的射流结构来计算余辉光曲线。我们制定了一种方法，可以根据给定的离轴GRB余辉反向构造射流结构，而无需假定该结构的任何功能形式。通过系统地应用我们的反演方法，我们发现，在中空锥，主轴，高斯和幂律射流结构等误差范围内，更多样化的射流结构与GRB 170817A观察到的余辉一致。此外，重建射流的总能量是任意的，与环境密度成正比（n ₀），如果参数满足简并组合$ n_0 \ varepsilon _ \ mathrm {B} ^ {（p + 1）/（p + 5）} \ varepsilon _ \ mathrm {e} ^ {4 （p-1）/（p + 5）} = \ mathrm {const。} $辨别不同形状的观测准确度必须低于6％，同时观察到光谱会破坏能量缩放的简并性断裂和视角。在我们的反演方法中确定射流结构，这是形成射流和传播的关键，这是在密度更高的环境中发生的更亮的余辉和可观察到的光谱破裂的未来事件的理想选择。