爱因斯坦探针快速X射线暂现源的射电后续观测
Radio Follow-Up of Einstein Probe Fast X-Ray Transients
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中文总结 AI 辅助
本文针对20个爱因斯坦探针2024年探测的快速X射线暂现源开展射电后续观测，发现2个存在射电对应体，揭示其异质性，下一代阵列将助力相关研究。
中文摘要 AI 辅助
快速X射线暂现源（FXTs）是短暂、明亮的软X射线辐射爆发，其物理起源仍不确定。爱因斯坦探针（EP）任务近期实现了这类事件的快速发现，为开展快速多波段后续观测提供了机会。我们针对2024年EP探测到的20个FXTs开展了协调的射电观测 campaign，核心部分为艾伦望远镜阵（ATA）的59个观测历元，采样爆发后约1至65天的时标，在1至8吉赫频段达到典型0.6至1.5毫央斯基的3σ灵敏度。其中2个FXTs——EP240315a和EP241021a存在射电对应体。对于EP241021a，15.5吉赫的AMI-LA监测显示其光变曲线在约30天达到峰值，流量密度Fν≈1.0毫央斯基；均分分析得出牛顿均分能量约3×10⁴⁹尔格，以及Γ_on≈1.3的 mildly 相对论性正对观测解。对EP240315a的多波段建模结合了新的甚大天线阵（VLA）测量数据与已发表的 MeerKAT、ATCA和eMERLIN数据，表明其早期辐射高度相对论性（Γ≳3）且随时间减速，符合喷流外流特征。这些探测结果与ATA的未探测结果覆盖了最明亮的伽马暴（GRB）和相对论性潮汐瓦解事件（TDE）余辉的光度范围，提示FXTs是包含相对论性和非相对论性爆发的异质群体。在类GRB红移先验下，我们的ATA 3σ极限对应观测帧特定光度阈值约10³²至10³³尔格·秒⁻¹·赫兹⁻¹；对于近邻事件（z≲0.2），Lν≲10³⁰至10³¹尔格·秒⁻¹·赫兹⁻¹。计划中的ATA升级及下一代阵列（SKA、DSA、ngVLA）将实现对FXT射电天区的灵敏、群体级射电研究。
英文摘要
Fast X-ray transients (FXTs) are brief, luminous bursts of soft X-ray emission whose physical origins remain uncertain. The Einstein Probe (EP) mission has recently enabled prompt discovery of these events, providing opportunities for rapid multi-wavelength follow-up. We present a coordinated radio observing campaign targeting 20 FXTs detected by the EP in 2024. The core consists of 59 epochs with the Allen Telescope Array (ATA), sampling post-burst timescales from $\sim$1 to $\sim$65 days and reaching typical $3σ$ sensitivities of 0.6--1.5\,mJy across 1--8\,GHz. Two FXTs---EP240315a and EP241021a---have radio counterparts. For EP241021a, AMI-LA monitoring at 15.5\,GHz reveals a light curve peaking at $\sim$30 days with $F_ν\approx1.0$\,mJy; equipartition analysis implies a Newtonian equipartition energy of $\sim3\times10^{49}$\,erg and a mildly relativistic on-axis solution with $Γ_{\rm on}\approx1.3$. Multi-frequency modelling of EP240315a, combining new VLA measurements with published MeerKAT, ATCA, and eMERLIN data, indicates highly relativistic early emission ($Γ\gtrsim3$) that decelerates with time, consistent with jetted outflow. The detections and ATA non-detections span luminosities overlapping the brightest GRB and relativistic tidal disruption event (TDE) afterglows, suggesting FXTs comprise a heterogeneous population including both relativistic and non-relativistic explosions. Under a GRB-like redshift prior, our $3σ$ ATA limits correspond to observer-frame specific-luminosity thresholds of $\sim10^{32}$--$10^{33}\,\mathrm{erg\ s^{-1}\ Hz^{-1}}$; for nearby events ($z\lesssim0.2$), $L_ν\lesssim10^{30\text{--}31}\,\mathrm{erg\ s^{-1}\ Hz^{-1}}$. Planned ATA upgrades and next-generation arrays (SKA, DSA, ngVLA) will enable sensitive, population-level radio studies of the FXT radio sky.
