Over 700 bright millisecond-duration radio transients, known as fast radio bursts (FRBs), have been identified to date. Nevertheless, the origin of FRBs remains unknown. Two repeating FRBs (FRB 20121102A and FRB 20190520B) have been verified to be associated with persistent radio sources (PRSs), making them the best candidates to study the nature of FRBs. Monitoring the variability in PRSs is essential for understanding their physical nature. We conducted 22 observations of the PRSs linked to FRB 20121102A and FRB 20190520B using the Karl G. Jansky Very Large Array, to study their variability. We have observed significant flux variability for the PRSs of FRB 20121102A and FRB 20190520B, with a confidence level exceeding 99.99%, based on the observations covering the longest timescale recorded to date. The observed variability of the two PRSs exhibits no significant difference in amplitude across both short and long timescales. We found that the radio-derived star formation rates of the two FRB hosts are significantly higher than those measured by the optical Hα emissions, indicating that their host galaxies are highly obscured or most radio emissions are not from star formation processes. The observed timescale of PRS flux evolution constrained the magnetic field of FRB 20121102A with B∥ ≳ 1 mG and FRB 20190520B with B∥ ≳ 0.1 mG.

中文翻译：

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快速射电暴的持续射电源的变化


迄今为止，已经确定了 700 多个明亮的毫秒持续时间的射电瞬变，称为快速射电暴 （FRB）。然而，FRB 的起源仍然未知。两个重复的 FRB（FRB 20121102A 和 FRB 20190520B）已被验证与持续性射电源 （PRS） 相关，使它们成为研究 FRB 性质的最佳候选者。监测 PRS 的可变性对于了解其物理性质至关重要。我们使用 Karl G. Jansky 甚大数组对与 FRB 20121102A 和 FRB 20190520B 相关的 PRS 进行了 22 次观察，以研究它们的可变性。我们观察到 FRB 20121102A 和 FRB 20190520B 的 PRS 的磁通量变化显著，置信度超过 99.99%，基于迄今为止记录的最长时间尺度的观测。观察到的两个 PRS 的变化在短期和长期时间尺度上均未表现出振幅的显着差异。我们发现，两个 FRB 宿主的射电衍生恒星形成速率明显高于光学 Hα 发射测得的速率，这表明它们的宿主星系被高度遮挡或大多数射电发射不是来自恒星形成过程。观察到的 PRS 磁通量演化时间尺度限制了 FRB 20121102A 的磁场，∥ ≳ 1 mG 和 FRB 20190520B 的磁场∥ ≳ 0.1 mG。