A Measurement of the Average Longitudinal Development Profile of Cosmic Ray Air Showers Between 10^{17}eV and 10^{18}eV

Abstract

The average extensive air shower longitudinal development profile as a function of shower age in the energy range from 10$^{17}$ to 10$^{18}$eV is measured using data from the hybrid HiRes/MIA experiment. An angular bin signal based Cerenkov light component subtraction method and a shower maximum fitting method using a local parabolic function are used to correct and normalize the data. The Gaisser-Hillas and Greisen functions work equally well for describing the shower profile. The Gaussian function is a poor fit. A simple scale-free function is proposed and fits the data equally well. The best-fit parameters for the above functions are determined.