  We performed ab-initio Particle-In-Cell (PIC) simulations of a pulsar
magnetosphere with electron-positron plasma produced only in the regions close
to the neutron star surface. We study how the magnetosphere transitions from
the vacuum to a nearly force-free configuration. We compare the resulting
force-free like configuration with ones obtained in a PIC simulation where
particles are injected everywhere as well as with macroscopic force-free
simulations. We found that although both PIC solutions have similar structure
of electromagnetic fields and current density distributions, they have
different particle density distribution. In fact in the injection from the
surface solution, electrons and positrons counterstream only along parts of the
return current regions and most of the particles leave the magnetosphere
without returning to the star. We also found that pair production in the outer
magnetosphere is not critical for filling the whole magnetosphere with plasma.
We study how the current density distribution supporting the global
electromagnetic configuration is formed by analyzing particle trajectories. We
found that electrons precipitate to the return current layer inside the light
cylinder and positrons precipitate to the current sheet outside the light
cylinder by crossing magnetic field lines contributing to the charge density
distribution required by the global electrodynamics. Moreover, there is a
population of electrons trapped in the region close to the Y-point. On the
other hand the most energetic positrons are accelerated close to the Y-point.
These processes can have observational signatures that, with further modeling
efforts, would help to distinguish this particular magnetosphere configuration
from others.
