GRB 220426A 加速相光球揭示的风约束喷流准直

中文摘要 AI 辅助

我们分析了费米/GBM 观测到的极亮伽马射线暴 GRB 220426A 的瞬时辐射，其时间分辨谱是所有伽马射线暴中测得的最窄谱之一。研究表明，最初约 5 秒内的观测结果与喷流仍处于初始辐射主导加速阶段时的发射信号相符。时间分辨谱使我们能以极高精度推断有效发射半径 r₀，发现 r₀ 约为 10¹⁰ 厘米量级，且随时间线性增加。这些结果与重联激波的理论预测一致，表明该伽马射线暴提供了重联激波存在与演化的首个清晰证据。基于该解释，观测到的线性增长持续时间远超纯喷流突破的预期，因此喷流准直必须持续到突破之后。我们提出，准直由有限、致密的类风暴周介质维持，这可重现观测到的瞬时辐射行为。研究结论为，前身星晚期质量损失可塑造最早的瞬时辐射，而光球辐射提供了一种独立于相互作用超新星约束、探测喷流准直及前身星周围最内层暴周介质（CBM）的方法。

英文摘要

We analyze the prompt emission of the exceptionally bright GRB 220426A observed by {\it Fermi}/GBM, whose time-resolved spectra are among the narrowest measured in any GRB. Here we show that observations during the first $\sim 5$~s are consistent with the signal being emitted while the jet was still in the initial radiation-dominated acceleration phase. The time-resolved spectra allow the effective launch radius, $r_0$, to be inferred with unusual precision. We find $r_0 \sim \mathrm{few} \times 10^{10}\,\mathrm{cm}$, increasing linearly with time. These findings match the theoretical expectation for the recollimation shock, implying that this GRB shows the first clear evidence for the existence and evolution of a recollimation shock. Using this interpretation, the linear increase observed is sustained over a period longer than expected from a pure jet breakout. Therefore, the jet collimation must have persisted even after breakout. We suggest that the collimation was maintained by a finite, dense, wind-like circumburst medium, which would reproduce the observed behavior of the prompt emission. We conclude that late-stage progenitor mass-loss can shape the earliest prompt emission and that the photospheric emission provides a way to probe both the jet collimation and the innermost region of the circumburst medium (CBM) surrounding the progenitor, independently of the constraints from interacting supernovae.

发表机构

• KTH Royal Institute of Technology（皇家理工学院）
• The Oskar Klein Centre（奥斯卡·克莱因中心）
• Bar-Ilan University（巴伊兰大学）

机构由 AI 辅助整理，请以论文原文为准。

补充信息

备注

Submitted. 18 pages + appendices