Fermi Gamma-Ray Pulsars: Understanding the High-energy Emission from Dissipative Magnetospheres

Based on the Fermi observational data, we reveal meaningful constraints for the dependence of the macroscopic conductivity (σ) of dissipative pulsar magnetosphere models on the corresponding spin-down rate, $\dot{E}$. Our models are refinements of the FIDO (Force-free Inside, Dissipative Outside) models, which have dissipative regions that are restricted on the equatorial current sheet outside of the the light-cylinder. Taking into account the observed cutoff energies of all of the Fermi pulsars and assuming that (a) the corresponding γ-ray pulsed emission is due to curvature radiation at the radiation-reaction-limit regime, and (b) this emission is produced at the equatorial current sheet near the light cylinder, we show that the Fermi data provide clear indications about the corresponding accelerating electric-field components. A direct comparison between the Fermi cutoff energies and the model ones reveals that σ increases with $\dot{E}$ for high $\dot{E}$-values, while it saturates for low ones. This comparison indicates also that the corresponding gap width increases toward low $\dot{E}$-values. Assuming the Goldreich–Julian flux for the emitting particles, we calculate the total γ-ray luminosity (L _γ). A comparison between the dependence of the Fermi L _γ-values and the model ones on $\dot{E}$ indicates an increase of the emitting particle multiplicity with $\dot{E}$. Our modeling, guided by the Fermi data alone, enhances our understanding of the physical mechanisms behind the high-energy emission in pulsar magnetospheres.