Low Frequency Radio Signals from Giant Air Showers

我们已经观测到与大阵雨有关的无线电信号。对于初级能量为10^<19>eV的阵雨，无线电信号可以在大约5公里的核心距离内观测到。主要观察到负单极信号，也可以在较低的频率下获得正单极和双极信号，其脉冲宽度分布在1 ~ 5mus之间。我们用一种新的发射模型进行了计算，该模型认为无线电信号是由于带负电荷的多余电子在电离损失过程中失加速度和大气电场的作用而发射的。在低于几兆电子伏的能量下，负电荷电子的过剩是显著的。然后我们假设带负电荷的多余电子的能量为1MeV，并且在穿过厚度为1g/cm^2的大气时被去加速。即使初级宇宙射线具有相同的能量，相同R处的计算场强取决于到达方向的天顶角（θ）和phi，并且与观测强度非常一致。分布也与该模型一致，因为在具有相同初级能量和到达方向的θ的阵雨中，φ为180度的阵雨给出了最大的场强。此外，该模型根据R， theta和phi预测正、负单极和双极信号。这一结果也与观测结果一致。然而，计算的脉冲宽度比观测信号的脉冲宽度小约三倍。如果考虑到系统的时间响应引起的脉冲变形和分析中采用的方法，就可以解释这种差异的部分原因。我们的计算表明，能量大于10^<20>eV的宇宙射线的到达方向和一次能量(E)分别可以在3度和0.1 log(E)的精度内测量。

We have observed radio signals associated with large air showers. For showers with primary energies of 10^<19>eV, radio signals can be observed at core distances within about 5km. Negative unipolar signals are mainly observed, while positive unipolar and bipolar signals are also obtained with rather low frequency and their pulse widths distribute from 1 to 5mus. We made a calculation with a new emission model in which radio signals are emitted due to deacceleration of negative charge excess electrons with a process of ionization loss and by the effect of the atmospheric electric field. The excess of negative charge electrons is significant at lower energies than several MeV. Then we have assumed that negative charge excess electrons have energies of 1MeV and are deaccelerated during passing through the atmosphere with thickness of 1g/cm^2. Even though primary cosmic rays have the same energies, calculated field intensities at same R depend on zenith angles(theta) of arrival directions and phi and are much consistent with observed intensities The distribution are also consistent with this model, since a shower with phi of 180 degrees gives the largest field intensities among showers with the same primary energies and theta of arrival direction. Furthermore, this model predicts positive and negative unipolar and bipolar signals according to R, theta and phi. This result is also consistent with observed results. However calculated pulse widths are smaller than those of observed signals by about three times. Some parts of this difference can be explained if we take into account of pulse deformation due to time response of the system and the employed method in the analysis. Our calculation shows that arrival directions and primary energies(E) of cosmic rays with energies above 10^<20>eV can be measured within an accuracy of 3 degrees and 0.1 in log(E) respectively.