利用 Allen Telescope Array 对 TRAPPIST-1 开展的无线电技术特征搜索
A Radio Technosignature Search of TRAPPIST-1 with the Allen Telescope Array
AI总结：
本研究结合 turboSETI 与 NbeamAnalysis 分析 ATA 对 TRAPPIST-1 的 28 小时观测，在 7 次预测 PPO 窗口内搜索窄带技术特征，未发现非人类信号并给出 EIRP 上限。
摘要：
行星—行星掩星（PPO）是指从地球视角看，同一系统中的一颗系外行星掩蔽另一颗系外行星。PPO 可能提供一个独特机会，用于观测来自地外智慧文明（ETI）无线电发射或雷达信号的无线电“溢出”：这些信号由较远的系外行星向较近的行星发送，目的是通信或科学探索。拥有许多紧密排列、低倾角行星的行星系统，例如 TRAPPIST-1，预计会频繁发生 PPO。本文使用窄带技术特征搜索代码 turboSETI，并结合新开发的 NbeamAnalysis 过滤流程，分析了 Allen Telescope Array（ATA）于 2022 年 10 月末至 11 月初在 0.9–9.3 GHz 频段针对 TRAPPIST-1 获取的 28 小时波束成形数据。在此观测窗口内，使用 NbodyGradient 代码预测了 7 次可能的 PPO 事件。该过滤流程通过剔除并非来自天空定位方向的信号，将最初 2500 万个候选信号缩减至 600 万个；随后依据一个幂律截断，从这些信号中确定了包含 11127 个候选信号的最终列表，该截断旨在根据信号在波束之间的衰减和形态相似性对其进行区分。所有信号均被绘图以供目视检查，其中发现 2264 个发生在 PPO 窗口内。我们报告未探测到非人类起源的信号；针对每次 PPO 事件计算的上限，在最小漂移信号情况下超过 2.17–13.3 TW 的 EIRP，在最大漂移情况下则为 40.8–421 TW。这项工作构成了迄今为止对 TRAPPIST-1 持续时间最长的单目标无线电 SETI 搜索。
英文摘要：
Planet-planet occultations (PPOs) occur when one exoplanet occults another exoplanet in the same system as seen from the Earth's vantage point. PPOs may provide a unique opportunity to observe radio "spillover" from extraterrestrial intelligences' (ETIs) radio transmissions or radar being transmitted from the further exoplanet towards the nearer one for the purposes of communication or scientific exploration. Planetary systems with many tightly packed, low-inclination planets, such as TRAPPIST-1, are predicted to have frequent PPOs. Here, the narrowband technosignature search code turboSETI was used in combination with the newly developed NbeamAnalysis filtering pipeline to analyze 28 hours of beamformed data taken with the Allen Telescope Array (ATA) during late October and early November 2022, from 0.9--9.3~GHz, targeting TRAPPIST-1. During this observing window, 7 possible PPO events were predicted using the NbodyGradient code. The filtering pipeline reduced the original list of 25 million candidate signals down to 6 million by rejecting signals that were not sky-localized and, from these, identified a final list of 11127 candidate signals above a power law cutoff designed to segregate signals by their attenuation and morphological similarity between beams. All signals were plotted for visual inspection, 2264 of which were found to occur during PPO windows. We report no detection of signals of non-human origin, with upper limits calculated for each PPO event exceeding EIRPs of 2.17--13.3 TW for minimally drifting signals and 40.8--421 TW in the maximally drifting case. This work constitutes the longest single-target radio SETI search of TRAPPIST-1 to date.
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