A study on the radiopulses from extensive air showers at metre wavelengths

Abstract

Radiopulses from extensive air showers (EAS) at 44, 60 and 80 MHz frequencies have been studied at the Cosmic Radiation Research Laboratory, Department of Physics, Gauhati University, India during 1971-78. The experimental arrangement set up for the investigation, consisted of (i) a Geiger- Mueller counter array and the associated circuits for the detection of near zenith EAS (gt/ 1016 eV), (ii) two sets of broad-side antenna systems for detection of radiopulses at 44 and 60 MHz frequencies and one set of stacked yagi arrays for 80 MHz frequency, and (iii) an automatic recording device that recorded the events displayed in the CRO. Data were collected for about 1150 hours, during the autumn and the winter seasons from 1972 to 1978, and altoge- ther 2729 showers were recorded. The emission of detectable radiopulses from EAS gt/ 1016 eV at different frequencies is confirmed. The experi- mental results support the theoretical prediction that the field strength of radioemission depends on the shower size and hence on the energy of the primary. An asymmetry has been noticed in the field-strength distribution of the radiopulses detected by the North-South (N-S) and the East-West (E-W) directed arrays. These obser- vations are in good agreement with the theory that charge separation mechanism is predominant in generating radiopulses from EAS, and that the radioemission is polarised in the E-W direction. The frequency spectra of the radiopulses at 44, 60 and 80 MHz frequencies are found to decrease in each case, with frequency. Further, the observation of radioemission at 80 MHz indicates the invalidity of the limit of radioemission above ~ 75 MHz frequency as was predicted by Askaryan (1962) according to his charge excess mechanism. The correlation between simultaneously produced radio-pulses from EAS at 60 and 80 MHz frequencies is studied for the first time in details. The statistical analyses indicate highly significant positive correlation between the radio-pulses at these two frequencies. It is concluded that the...