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arXiv 0809.2751astro-ph
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用LOPES测量cosmic ray空气簇射射电发射的频谱

Frequency spectra of cosmic ray air shower radio emission measured with LOPES

A. Nigl

备注：
13 pages, 21 figures. Nigl, A. et al. (LOPES Collaboration), Frequency spectra of cosmic ray air shower radio emission measured with LOPES, accepted by A&A on 17/06/2008
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摘要：

目的：我们希望研究宇宙射线空气簇射在100 PeV（1017 eV）附近的射电发射的光谱依赖性。方法：我们用偶极干涉仪LOPES（LOFAR Prototype Station）观测了宽频带的短射电脉冲，该仪器由一个名为Karlsruhe Shower Core and Array Detector（KASCADE）的粒子探测器阵列触发。LOFAR是低频阵列。为了这个分析，23个强的空气淋浴事件被选择使用KASCADE的参数。结果：所产生的电场谱向高频衰减。平均电场谱符合指数规律或幂律规律。得到的光谱斜率在不确定性范围内是不一致的，并且它比基于CORSIKA（KASCADE的宇宙射线模拟）模拟的空气簇射的蒙特卡罗模拟得到的斜率稍陡。最强的事件之一是在LOPES附近的雷暴活动期间测量的，并显示出测量的最长脉冲长度为110 ns，光谱斜率为-3.6。结论：我们用两种不同的方法表明，空气簇射无线电发射的频谱可以在事件的基础上重建，只有24个偶极子天线同时在很宽的频率范围内。根据所获得的频谱斜率，最大功率在40 MHz以下发射。此外，功率降低到较高频率表明由簇射盘厚度确定的相干性损失。我们的结论是，更宽的带宽，更大的收集面积，和更长的基线，将提供的LOFAR，是必要的，以进一步调查宇宙线空气簇射的相干性，脉冲长度和光谱斜率的关系。

英文摘要：

AIMS: We wish to study the spectral dependence of the radio emission from cosmic-ray air showers around 100 PeV (1017 eV). METHODS: We observe short radio pulses in a broad frequency band with the dipole-interferometer LOPES (LOFAR Prototype Station), which is triggered by a particle detector array named Karlsruhe Shower Core and Array Detector (KASCADE). LOFAR is the Low Frequency Array. For this analysis, 23 strong air shower events are selected using parameters from KASCADE. RESULTS: The resulting electric field spectra fall off to higher frequencies. An average electric field spectrum is fitted with an exponential, or alternatively, with a power law. The spectral slope obtained is not consistent within uncertainties and it is slightly steeper than the slope obtained from Monte Carlo simulations based on air showers simulated with CORSIKA (Cosmic Ray Simulations for KASCADE). One of the strongest events was measured during thunderstorm activity in the vicinity of LOPES and shows the longest pulse length measured of 110 ns and a spectral slope of -3.6. CONCLUSIONS: We show with two different methods that frequency spectra from air shower radio emission can be reconstructed on event-by-event basis, with only two dozen dipole antennae simultaneously over a broad range of frequencies. According to the obtained spectral slopes, the maximum power is emitted below 40 MHz. Furthermore, the decrease in power to higher frequencies indicates a loss in coherence determined by the shower disc thickness. We conclude that a broader bandwidth, larger collecting area, and longer baselines, as will be provided by LOFAR, are necessary to further investigate the relation of the coherence, pulse length, and spectral slope of cosmic ray air showers.

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