发表机构
Columbia University; Flatiron Institute（哥伦比亚大学; 平顿研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出快速射电暴色散量变化源于超新星抛射物受中心引擎X射线光电离，模型预测活动增强伴随DM上升，并解释FRB 121102的DM演化。
AI 中文摘要
在发现来自银河系磁星的硬X射线耀发伴随明亮的射电暴之后，磁星成为快速射电暴（FRB）的首选引擎。多个重复暴源表现出随时间变化的旋转测量量，以及致密、空间重合的持续同步辐射射电辐射，这与高能粒子星云一致，并被年轻的超新星抛射物所约束。重复FRB的色散量（DM）的长期变化也已被观测到，为其局部环境提供了补充探针；例如，FRB 121102的DM在2019年之前持续上升，随后在近几年下降。尽管上升的DM演化被归因于冲击电离，但受冲击的抛射物可以通过金属线发射有效冷却，并可能重新复合，特别是当它与较冷气体湍流混合时。在此，我们认为观测到的量级和时间尺度的DM变化，源于受时变中心引擎X射线照射的超新星抛射物的电离状态变化。主导的快速变化贡献来自膨胀星云扫过的致密、弱电离壳层，其电离和复合时间远短于更延展的抛射物。该模型预测，增强的FRB活动应伴随DM上升，其响应在电离/复合时间上被平滑，叠加在膨胀抛射物引起的较慢长期下降之上；在FRB 121102中，DM最大值出现在接近2018-2019年活动高发期，包括2019年FAST暴风暴。如果最近报道的FRB 121102活动复苏持续，该模型预测其DM下降应趋于平缓，并可能在未来几年逆转进入新的上升期。
英文摘要
Magnetars became favored engines of fast radio bursts (FRBs) following the discovery of a luminous radio burst coincident with a hard X-ray flare from a Galactic magnetar. Several repeating FRB sources exhibit time-variable rotation measures and compact, spatially coincident persistent radio emission, consistent with energetic-particle nebulae confined by young supernova ejecta. Secular changes in the dispersion measure (DM) of repeating FRBs have also been observed, offering a complementary probe of their local environments; for example, the DM of FRB 121102 rose until 2019 before declining in recent years. Although rising DM evolution has been attributed to shock ionization, shocked ejecta can cool efficiently through metal-line emission and recombine, especially if mixed with cooler gas. Here we argue that DM variations of the observed magnitude and timescale instead arise from changes in the ionization state of supernova ejecta irradiated by X-rays from a time-variable central engine. The dominant rapidly variable contribution comes from the dense, weakly ionized shell swept up by the expanding nebula, whose ionization and recombination times are shorter than those of the more extended ejecta. The model predicts that enhanced FRB activity should be accompanied by rising DM, with a response smoothed over the ionization/recombination time and superposed on a slower secular decline from ejecta expansion. In FRB 121102, the DM maximum occurred close to the burst-rich 2018-2019 activity episodes. If the recently reported renewed activity is sustained, its DM decline should flatten and may reverse into a fresh rise over the coming years.
Commentssubmitted to ApJ
