爱因斯坦探针探测到的快速X射线瞬变扩展了相对论喷流的物理参数空间
Einstein Probe Fast X-ray Transients Extend the Physical Parameter Space of Relativistic Jets
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中文总结 AI 辅助
研究爱因斯坦探针探测到的快速X射线瞬变，用多种喷流结构研究其物理起源，发现标准喷流结构能解释部分能量，但不能完全解释一些高能FXTs的峰值能量值，表明其可能探测到参数空间新区域的相对论爆炸，促使进一步研究。
中文摘要 AI 辅助
爱因斯坦探针（EP）任务探测到的快速X射线瞬变（FXTs）与典型的长（II型）伽马射线暴相比，具有极低的光谱峰值能量。一些河外瞬变与X射线闪（XRFs）有现象学上的相似性，但FXTs的物理起源仍不确定。本文利用与II型伽马射线暴相关的各种喷流结构研究EP探测到的FXTs，并检验这些FXTs属于已知伽马射线暴的同一固有群体但从喷流轴大角度观测的假设。通过可探测性估计评估它们在观测到的等效各向同性能量-峰值能量平面中的分布。发现标准的单组分和多组分喷流结构可以重现轴外事件（如GRB 170817A和低光度伽马射线暴）的能量，同时也能产生与中等轴外观测者在等效各向同性能量-峰值能量连续体下端的XRFs一致的能量。然而，仅标准II型伽马射线暴的视角效应无法解释一些高能FXTs中观测到的峰值能量值。这种差异表明，EP探测到的FXTs不太可能仅被解释为轴外观测到的经典伽马射线暴，而可能探测到参数空间中一个以前未充分探索区域的相对论爆炸。特别是，这些瞬变可能与较低的洛伦兹因子、坍缩核心中角动量的减少或替代的喷流结构和发射机制有关。我们的结果促使进一步研究来检验这些情况，并限制FXTs前身及其外流的物理性质。
英文摘要
Fast X-ray Transients (FXTs) detected by the Einstein Probe (EP) mission possess exceptionally low spectral peak energies compared to typical long (Type II) GRBs. Some of these extragalactic transients show phenomenological similarities to X-ray flashes (XRFs), but the physical origins of FXTs remain uncertain. In this work, we investigate EP-detected FXTs using various jet structures relevant to Type II GRBs and test the hypothesis that these FXTs belong to the intrinsically same population of known GRBs but viewed at large angles from the jet axis. We apply detectability estimates to evaluate their distribution in the observed E_iso-E_p plane. We find that standard single- and multi-component jet structures can reproduce the energetics of off-axis events such as GRB 170817A and low-luminosity GRBs (llGRBs), while also yielding energetics consistent with XRFs at the lower end of the E_iso-E_p continuum for moderately off-axis observers. However, viewing-angle effects of standard Type II GRBs alone cannot account for the E_p values observed in some energetic FXTs. This tension suggests that EP-detected FXTs are unlikely to be explained solely as classical GRBs viewed off-axis, and may instead probe relativistic explosions in a previously underexplored region of parameter space. In particular, these transients may be associated with lower Lorentz factors, reduced angular momentum in the collapsing core, or alternative jet structures and emission mechanisms. Our results motivate further studies to test these scenarios and constrain the physical properties of FXT progenitors and their outflows.
