[论文解读] Sporadic radio pulses from a white dwarf binary at the orbital period

Iris de Ruiter, Kaustubh Rajwade+15 more|arXiv (Cornell University)|Aug 21, 2024

Stellar, planetary, and galactic studies被引用 5

一句话总结

发现 ILT J1101+5521，一对白矮星–M型矮星双星，发出散发的、高度偏振的射电脉冲，周期等于轨道周期（约 125.52 分钟）。

ABSTRACT

Recent observations have revealed rare, previously unknown flashes of cosmic radio waves lasting from milliseconds to minutes, and with periodicity of minutes to an hour. These transient radio signals must originate from sources in the Milky Way, and from coherent emission processes in astrophysical plasma. They are theorized to be produced in the extreme and highly magnetised environments around white dwarfs or neutron stars. However, the astrophysical origin of these signals remains contested, and multiple progenitor models may be needed to explain their diverse properties. Here we present the discovery of a transient radio source, ILT J1101+5521, whose roughly minute-long pulses arrive with a periodicity of 125.5 minutes. We find that ILT J1101+5521 is an M dwarf -- white dwarf binary system with an orbital period that matches the period of the radio pulses, which are observed when the two stars are in conjunction. The binary nature of ILT J1101+5521 establishes that some long-period radio transients originate from orbital motion modulating the observed emission, as opposed to an isolated rotating star. We conclude that ILT J1101+5521 is likely a polar system where magnetic interaction has synchronised the rotational and orbital periods of the white dwarf. Magnetic interaction and plasma exchange between two stars has been theorized to generate sporadic radio emission, making ILT J1101+5521 a potential low-mass analogue to such mechanisms.

研究动机与目标

• 确定 LOFAR 探测到的神秘长周期射电瞬变的性质。
• 确定射电脉冲的周期性是否与轨道运动还是自转有关。
• 表征伴星、双星参数及发射机制的含义。
• 评估多波长对应源及系统的演化状态（极化型与其他双星）。
• 约束长周期瞬变中相干射电发射的物理起源。

提出的方法

• 在 8 s–1 h 图像快照上使用 LPF 流水线在 LoTSS 数据中搜索瞬变源。
• 定位 ILT J1101+5521 并用 WSClean 和 PySE 重新成像以确认天体物理性质。
• 计算脉冲到达时间并使用 TEMPO2 进行相位连贯定时。
• 使用径向速度光谱学对双星进行建模以约束伴星质量与倾角。
• 利用广域光度测量通过贝叶斯推断拟合伴星（M 型矮星 + 白矮星）模型。
• 分析极化和色散测量以推断磁场和等离子体性质。

实验结果

研究问题

• RQ1 125.52 分钟的周期是双星的轨道周期还是紧致对象的自转周期？
• RQ2 射电脉冲是否在特定轨道相位更易发生，这对发射机制有何含义？
• RQ3 伴星的性质及系统的演化状态（极化型、前极化型或其他）为何？
• RQ4 多波长数据能对吸积活动和磁场几何提供哪些约束？

主要发现

• 在 2015–2020 年的 LOFAR 观测中侦测到七个射电脉冲，峰值通量密度为 41–256 mJy/beam。
• 脉冲周期性为 125.51950(4) 分钟，周期导数上限为 3.04×10^-11 s s^-1。
• 脉冲在上合位（superior conjunction）发生，使射电周期性与轨道周期相关。
• 天体测量和光谱数据确认伴星为白矮星，供体为 M4.5V，系统夹角<40°，对 WD 质量 ≥0.2 M⊙ 的情况。
• 线性偏振分数高达 51%（RM ~4.5–4.7 rad m^-2），未检测到圆偏振；DM ~16±6 pc cm^-3。
• 该系统与极化型（磁性白矮星）构型一致，旋转与轨道同步，几乎无持续吸积（没有强X射线发射）。