Studies on electromagnetic waves both at optical and radiofrequency regions from extensive air showers

Abstract

Associated production of radio pulses and optical Cerenkov pulses from extensive air showers (EAS) has been studied at the Physics Laboratory, Gauhati University, Assam, India, during 1972-75. Two broad-side dipole antenna systems for detecting radio pulses from EAS at 30 and 44 MHz were constructed. An optical Cerenkov detector compri-sing a parabolic reflector and a photomultiplier tube was also designed and used for detecting the optical Cerenkov pulses from EAS. A Geiger-Mueller counter array and the associated circuits were designed for EAS particle detection. An automatic recording device was also constructed. Data were collected for about 700 hours, during which altogether 417 optical Cerenkov pulses and 163 radio pulses were recorded. First, analyses of the optical Cerenkov pulse height distribution are made and the results are compared with a theoretical curve generated by an equation developed by the author. Results are also compared with those of other workers. Secondly, correlation between the optical Cerenkov pulses and the radio pulses are studied in details. The statistical analyses indicate negative correlation between the two types of pulses at both the frequencies. The negativity at 30 MHz is found to be in-significant, whereas at 44 MHz it is significant both at 5% and at 1% level of significance. The negativity in the correlation indicates that Cerenkov mechanism may not be the only mechanism for production of the radio pulses. Analyses indicate that the true mechanism responsible for the production of radio pulses is predominantly charge acceteralion mechanism as has also been pointed out by Kahn and Lerche, although there is some contribution from the low frequency end of Cerenkov radiation.