Off-axis jet scenario for early afterglow emission of low-luminosity gamma-ray burst GRB 190829A
Off-axis jet scenario for early afterglow emission of low-luminosity gamma-ray burst GRB 190829A
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DOI：
10.1093/mnras/stab1273
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发表时间：
2021-01
影响因子：
4.8
通讯作者：
Yuri Sato;K. Obayashi;R. Yamazaki;K. Murase;Y. Ohira
中科院分区：
文献类型：
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作者：
Yuri Sato;K. Obayashi;R. Yamazaki;K. Murase;Y. Ohira
最近，地基成像大气切伦科夫望远镜报道了从一些伽马射线暴（GRB）中探测到甚高能（VHE）伽马射线。其中一个GRB 190829 A是由雨燕卫星触发的，在爆发开始后约2 × 104秒，H.E.S.S.探测到VHE伽马射线发射。具有显著性。该事件具有各向同性的等效γ射线能量远小于典型长伽玛暴的特征，X射线和光学余辉的消色差峰值约为1.4 × 103 s。在这里，我们提出了一个离轴射流的情况下，解释这些观测结果。在这个模型中，相对论性聚束效应是造成各向同性γ射线能量和谱峰能量明显较小的原因。使用喷射余辉模型，我们发现，窄射流，它具有初始洛仑兹因子为350和初始射流开口半角为0.015弧度，离轴观察可以描述所观察到的消色差行为的X射线和光学余辉。另一个宽的、载有重子的喷流是后期X射线和射电发射所必需的。根据我们的模型，H.E.S.S.在2 × 104 s时，可能来自于窄喷流的同步自康普顿过程。
Recently, ground-based Imaging Atmospheric Cherenkov Telescopes have reported the detection of very-high-energy (VHE) gamma-rays from some gamma-ray bursts (GRBs). One of them, GRB 190829A, was triggered by the Swift satellite, and about 2 × 104 s after the burst onset the VHE gamma-ray emission was detected by H.E.S.S. with ∼5σ significance. This event had unusual features of having much smaller isotropic equivalent gamma-ray energy than typical long GRBs and achromatic peaks in X-ray and optical afterglow at about 1.4 × 103 s. Here, we propose an off-axis jet scenario that explains these observational results. In this model, the relativistic beaming effect is responsible for the apparently small isotropic gamma-ray energy and spectral peak energy. Using a jetted afterglow model, we find that the narrow jet, which has the initial Lorentz factor of 350 and the initial jet opening half-angle of 0.015 rad, viewed off-axis can describe the observed achromatic behaviour in the X-ray and optical afterglow. Another wide, baryon-loaded jet is necessary for the later-epoch X-ray and radio emissions. According to our model, the VHE gamma rays observed by H.E.S.S. at 2 × 104 s may come from the narrow jet through the synchrotron self-Compton process.