An interpretation of AGASA (Akeno Giant Air Shower Array) data by comparing
the experimental results with the simulated ones by CORSIKA (COsmic Ray
SImulation for KASCADE) has been made. General features of the electromagnetic
component and low energy muons observed by AGASA can be well reproduced by
CORSIKA. The form of the lateral distribution of charged particles agrees well
with the experimental one between a few hundred metres and 2000 m from the
core, irrespective of the hadronic interaction model studied and the primary
composition (proton or iron). It does not depend on the primary energy between
10^17.5 and 10^20 eV as the experiment shows. If we evaluate the particle
density measured by scintillators of 5 cm thickness at 600 m from the core
(S_0(600), suffix 0 denotes the vertically incident shower) by taking into
account the similar conditions as in the experiment, the conversion relation
from S_0(600) to the primary energy is expressed as E [eV] = 2.15 x 10^17 x
S_0(600)^1.015, within 10% uncertainty among the models and composition used,
which suggests the present AGASA conversion factor is the lower limit. Though
the form of the muon lateral distribution fits well to the experiment within
1000 m from the core, the absolute values change with hadronic interaction
model and primary composition. The slope of the rho_mu(600) (muon density above
1 GeV at 600 m from the core) vs. S_0(600) relation in experiment is flatter
than that in simulation of any hadronic model and primary composition. Since
the experimental slope is constant from 10^15 eV to 10^19 eV, we need to study
this relation in a wide primary energy range to infer the rate of change of
chemical composition with energy. keywords: cosmic ray, extensive air shower,
simulation, primary energy estimation PACS number ; 96.40.De, 96.40.PqComment: 30 pages, 15 figures, accepted by Astroparticle Physics at 6. Dec
199