  We use thermodynamic and neutron scattering measurements to study the effect
of oxygen annealing on the superconductivity and magnetism in
Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-\delta}$. Although the transition temperature
$T_c$ measured by susceptibility and superconducting coherence length increase
smoothly with gradual oxygen removal from the annealing process, bulk
superconductivity, marked by a specific heat anomaly at $T_c$ and the presence
of a neutron magnetic resonance, only appears abruptly when $T_c$ is close to
the largest value. These results suggest that the effect of oxygen annealing
must be first determined in order to establish a Ce-doping dependence of
antiferromagnetism and superconductivity phase diagram for electron-doped
copper oxides.
