AI 中文总结
研究GRB 260226A的超快速余辉，利用费米望远镜观测其MeV-GeV辐射，发现其衰减规律无法用标准同步辐射解释，提出外逆康普顿辐射机制，揭示瞬时辐射对大质量恒星环境的重塑作用。
AI 中文摘要
长伽马射线暴通常由一些快速旋转的大质量恒星核心坍缩后喷出的相对论性喷流提供能量，内部耗散将部分喷流能量释放为高度变化的MeV瞬时辐射，剩余动能则驱动喷流与周围介质发生外激波，产生所谓的余辉。在余辉最初的几分钟内，不稳定的喷流会将能量传递给外激波，而MeV-GeV能量范围的早期余辉辐射很少被观测到，因为余辉的出现可能会被瞬时辐射掩盖。在此，我们报告对GRB 260226A的特殊观测结果，该观测由费米大面积望远镜完成，记录了来自某伽马射线暴的100 MeV以上光子数量最多的一次观测。这些数据使我们能够以空前的细节重建余辉在瞬时辐射阶段出现时的热光度演化。余辉成分在约50 MeV处达到峰值后迅速衰减，先以t⁻¹.⁵的衰减率变化，约一分钟后转变为超快速的t⁻².⁸衰减。这种行为无法用冷介质中传播的 blast wave 产生的标准同步辐射来解释，我们将其解释为在致密、充满正负电子对的恒星风环境中，新加热的电子对瞬时光子冷却时产生的外逆康普顿辐射。GRB 260226A因此表明，MeV-GeV观测可直接揭示外激波的形成，且大质量恒星环境会被瞬时辐射显著重塑。
英文摘要
Long-duration gamma-ray bursts are typically powered by relativistic jets launched after the core collapse of some rapidly rotating massive stars. Internal dissipation releases part of the jet energy as highly variable MeV prompt emission, while the remaining kinetic energy drives an external shock into the surrounding medium and produces the so-called afterglow. During the first minutes of the afterglow, the unsteady jet transfers energy to the external shock. The early afterglow emission in MeV-GeV energies is rarely observed because the emergence of afterglow can be overshined by the prompt emission. Here we report exceptional observations of GRB 260226A with the Fermi Large Area Telescope, which recorded the largest number of photons above 100 MeV from a gamma-ray burst. These data allow us to reconstruct the evolution of the bolometric flux of the afterglow from its emergence during the prompt emission phase with unprecedented detail. The afterglow component peaks near 50 MeV and fades rapidly, first as t$^{-1.5}$ and then transiting to an ultra-fast t$^{-2.8}$ decay after about one minute. This behavior cannot be explained by standard synchrotron emission from a blast wave propagating into a cold medium. We interpret it as external inverse Compton radiation from freshly heated electrons cooling on prompt photons in a dense, pair-loaded stellar wind. GRB 260226A therefore shows that MeV-GeV observations can directly reveal the formation of the external shock and the massive-star environment is significantly reshaped by the prompt emission.
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