We present the preliminary results of a search for transient Electromagnetic Pulses (EMP) associated with the impact of meteoroids on the lunar surface as observed with the Arecibo Observatory ALFA (Arecibo L-band Feed Array) system. The ALFA system is a cluster of seven, dual-linear polarization feeds/beams arranged in a hexagonal manner and operated in the protected L-band region centered at 1.41 GHz. We analyzed 8 TB of data totaling nearly 5.5 h of on- and off-moon observations made in February 2016. We demonstrate the observing strategy and time–frequency methods for the detection and removal of the local-radar transient interference signals while identifying potential EMPs. Local out of band radar interference signals are observed as intermodulation artifacts in the protected L-band. Seven transient wideband EMP events with time scales of less than 10 μs have been detected following the extensive vetting process we describe. Assuming that these EMP-like events originate from gram-sized meteoroid strikes and using very approximate hypervelocity impact, plasma production theory, and EMP generation theory, we estimate the progenitor impact meteoroid kinetic energy to be approximately 1.8 × 107 J. Assuming that the observed EMPs are the result of 10 g meteoroid impacts, the resultant meteoroid flux is 3 × 10−7 km−2 h−1 based solely on lunar surface area observed and net observing period. Implications of the observed transient EMP events, measured lunar noise temperature and the comparison with energy estimates derived from the existing lunar impact optical observations are also discussed.

中文翻译：

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阿雷西博 ALFA 阵列观测以寻找月球流星撞击电磁脉冲

我们展示了通过阿雷西博天文台 ALFA（阿雷西博 L 波段馈电阵列）系统观察到的与流星体对月球表面的影响相关的瞬态电磁脉冲 (EMP) 搜索的初步结果。ALFA 系统由七个双线性极化馈源/波束组成，以六边形方式排列，并在以 1.41 GHz 为中心的受保护 L 波段区域内运行。我们分析了 2016 年 2 月进行的近 5.5 小时月内和月外观测的 8 TB 数据。我们展示了用于检测和去除本地雷达瞬态干扰信号同时识别潜在 EMP 的观测策略和时频方法. 本地带外雷达干扰信号在受保护的 L 波段中被观察为互调伪影。在我们描述的广泛审查过程之后，已检测到时间尺度小于 10 μs 的七个瞬态宽带 EMP 事件。假设这些类 EMP 事件源自克级流星体撞击，并使用非常近似的超高速撞击、等离子体产生理论和 EMP 生成理论，我们估计前体撞击流星体动能约为 1.8 × 107 J。假设观测到EMP 是 10 g 流星体撞击的结果，所得流星体通量为 3 × 10−7 km−2 h−1，仅基于观测到的月球表面积和净观测周期。还讨论了观察到的瞬态 EMP 事件、测量的月球噪声温度以及与现有月球撞击光学观测得出的能量估计值的比较的影响。