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arXiv 2409.08485astro-ph.HEhep-ph
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基于光深论证对 GRB 221009A 中 MeV 发射线物理的稳健约束

Robust Constraints on the Physics of the MeV Emission Line in GRB 221009A from Optical Depth Arguments

Shu-Xu Yi, Zhen Zhang, Emre Seyit Yorgancioglu, Shuang-Nan Zhang, Shao-Lin Xiong, Yan-Qiu Zhang

AI总结:

本文通过光深论证约束 GRB 221009A 中 MeV 发射线的物理条件,确定正负电子对的产生与湮灭半径,建立自洽物理图像,并提出正负电子对产生判据及热辐射预言。

摘要:

史上最亮的伽马射线暴(GRB)GRB 221009A 是首个在其瞬时辐射谱中观测到发射线(最高达 37 MeV)的伽马射线暴。该现象可自然地解释为在 GRB 相对论性喷流中经多普勒增亮的正负电子对湮灭线。在本工作中,我们反复运用简单的光深论证,对产生可观测正负电子对湮灭线所必需的不同物理过程进行分析。该方法对发射线的物理性质给出了稳健的约束:我们得出结论,在 GRB 221009A 中,正负电子对产生于距中心引擎大于 $4.3\times 10^{15}$ cm 的半径处,并在 $1.4\times 10^{16}$ cm 至 $4.3\times 10^{16}$ cm 之间的区域发生湮灭。基于这些约束,我们建立了一个关于正负电子对产生、冷却和湮灭的自洽物理图像。我们还推导出 GRB 瞬时辐射中正负电子对产生的判据:$E_{\rm{iso}} \gtrsim3.3\times 10^{53} E_{\rm{peak},100} (1+z) R^2_{\rm{prod},16}~\text{erg}$。利用该判据,我们发现了数十个候选 GRB,它们可能在瞬时辐射中产生正负电子对并发生湮灭。根据该判据,GRB 221009A 具有最高的可能性。我们还预言在瞬时辐射阶段存在一种热辐射,其黑体温度随时间演化,并扫过软 X 射线波段。

英文摘要:

The brightest-of-all-time gamma-ray burst (GRB), GRB 221009A, is the first GRB observed to have emission line (up to 37 MeV) in its prompt emission spectra. It is naturally explained as \pair annihilation line that was Doppler boosted in the relativistic jet of the GRB. In this work, we repeatedly apply the simple optical depth argument to different physical processes necessary to produce an observable \pair annihilation line. This approach results in robust constraints on the physics of the line: We conclude that in GRB 221009A, the \pair pairs were produced at a radius greater than $4.3\times 10^{15}$\,cm from the central engine, and annihilated in a region between $1.4\times 10^{16}$\,cm and $4.3\times 10^{16}$\,cm. From these constraints, we established a self-consistent picture of \pair production, cooling, and annihilation. We also derived a criterion for pair production in the GRB prompt emission: $E_{\rm{iso}} \gtrsim3.3\times 10^{53} E_{\rm{peak},100} (1+z) R^2_{\rm{prod},16}~\text{erg}$. Using this criterion, we find tens of candidate GRBs that could have produced \pair in prompt emissions to annihilate. GRB 221009A is with the highest likelihood according to this criterion. We also predict the presence of a thermal radiation, with a time-evolving black body temperature, sweeping through soft X-ray during the prompt emission phase.

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