Gamma Ray and Hadron generated Čerenkov Photon Spectra at Various Observation Altitudes

We study the propagation of Čerenkov photons generated by Very High Energy γ−rays and hadrons in the atmosphere. The photon production height distributions are estimated from semi-empirical methods and compared with those derived by standard simulation techniques. Incident spectra at various observation altitudes are then derived after applying wavelength dependent corrections due to photon attenuation in the atmosphere during the propagation of photons from the height of production to the height of observation. These are generated both for γ− and hadron primaries of various energies. The derived production height distributions agree very well with those generated by the simulation package ‘CORSIKA’ at all energies and for both γ−ray and proton primaries. The incident photon spectra are found to be both altitude dependent and primary energy dependent. The peak of the incident spectrum shifts towards the shorter wavelength with increasing altitude of observation for a given primary. Also the peak of the photon spectrum shifts towards the shorter wavelength with increasing energy of the primary at given altitude. The fraction of the UV component in the incident Čerenkov spectrum is