发表机构
Cornell University; University of Toronto; Liverpool John Moores University; University of Utah; Massachusetts Institute of Technology; NSF NOIRLab（康奈尔大学; 多伦多大学; 利物浦约翰摩尔斯大学; 犹他大学; 麻省理工学院; 美国国家光学红外天文研究实验室）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过多波段观测与建模，揭示软X射线闪GRB 250419A由低动能高洛伦兹因子喷流驱动，支持XRF为经典伽马射线暴向低能量延伸的观点。
AI 中文摘要
软X射线闪（XRF）被预测来自多种假设现象，包括“脏火球”（具有显著重子负载的相对论性喷流）以及从边缘离轴视角观测到的伽马射线暴。对于给定的暴，需要详细的多波段观测来区分可能的 progenitors 场景，但拥有此类数据的XRF数量仍然很少。这里我们展示了GRB 250419A的X射线、光学和射电（毫米到厘米）数据，这是一个由天基多波段天文变量观测者（SVOM）发现的XRF（峰值能量$E_p<4\\,$keV）。我们观察到X射线和光学波段存在清晰的消色差拐折，并且射电发射中可能有两个光谱成分。余辉类似于长持续时间伽马射线暴群体，但光度略低，且光学余辉在$\lesssim2\\,$天时具有异常浅的衰减阶段。我们发现该事件很好地由一个高洛伦兹因子、低动能（$E\sim10^{49}$-$10^{50}\\,$erg）的喷流解释，其能量注入可能源于径向分层和/或喷流从边缘离轴视角观测。我们得出结论，至少一些X射线闪是经典伽马射线暴向更低能量的延伸。
英文摘要
Soft X-ray flashes (XRFs) are predicted from a variety of hypothesized phenomena, including "dirty fireballs" (relativistic jets with significant baryon loading), and gamma-ray bursts viewed marginally off-axis. For a given burst, detailed multiwavelength observations are necessary for distinguishing between possible progenitor scenarios, but the number of XRFs with such data remains small. Here we present X-ray, optical, and radio (mm to cm) data of GRB 250419A, an XRF (with peak energy $E_p<4\,$keV) discovered by the Space-based multi-band astronomical Variable Objects Monitor. We observe a clear achromatic break in the X-ray and optical bands, and likely two spectral components in the radio emission. The afterglow is similar to the long-duration gamma-ray burst population, but slightly underluminous, and the optical afterglow has an unusually shallow decay phase at $\lesssim2\,$d. We find that the event is well explained by a high-Lorentz factor jet with low kinetic energy ($E\sim10^{49}$-$10^{50}\,$erg), with energy injection that could arise from radial stratification and/or the jet being viewed marginally off-axis. We conclude that at least some X-ray flashes are an extension of classical gamma-ray bursts down to lower energies.
Comments30 pages, 10 figures, submitted to ApJ
