  Correlation between emitted particles from a thermalized medium carry
important information about the space-time extent and the dynamics of the
particle emitting source. Pion emission source functions S(r) have been
measured in PHENIX using an imaging technique, and it has been found that it
contains a heavy (power-law) tail. It leads us to the assumption that there is
a halo of secondary pions, surrounding the core system that undergoes the
hydrodynamical evolution. THERMINATOR, a Monte Carlo event generator designed
for studies in relativistic heavy-ion collisions is used to model and
investigate the influence of resonance decays on the tail of particle emission
source. It lacks the implementation of rescattering, which, as we have learnt
from previous Hadron Rescattering Code simulations, is a possible explanation
of the power-law tail. Our studies also have shown that none of the pion
sources alone are responsible for the tail: either the resonance decays or
rescattering or a combination of these effects is a possible cause of the heavy
tail.
