  We reinvestigate the radio pulsar ``death lines'' within the framework of two
different types of polar cap acceleration models, i.e., the vacuum gap model
and the space-charge-limited flow model, with either curvature radiation or
inverse Compton scattering photons as the source of pairs. General relativistic
frame-dragging is taken into account in both models. We find that the inverse
Compton scattering induced space-charge-limited flow model can sustain strong
pair production in some long-period pulsars, which allows the newly detected
8.5s pulsar PSR J2144-3933 to be radio loud, without assuming a special neutron
star equation-of-state or ad hoc magnetic field configurations.
