Outer gap accelerator closed by magnetic pair-creation process

Abstract

We discuss outer gap closure mechanism in the trans-field direction with the magnetic pair-creation process near the stellar surface. The gap closure by the magnetic pair-creation is possible if some fraction of the pairs are produced with an outgoing momentum. By assuming that multiple magnetic field will affect the local field near the stellar surface, we show a specific magnetic field geometry near the stellar surface resulting in the outflow of the pairs. Together with the fact that the electric field is weak below null charge surface, the characteristic curvature photon energy emitted by incoming particles, which were accelerated in the outer gap, decreases drastically to $\sim 100$MeV near the stellar surface. We estimate the height measured from the last-open field line, above which 100MeV photons is converted into pairs by the magnetic pair-creation. We also show the resultant multiplicity due to the magnetic pair-creation process could acquire $M_{e^{\pm}}\sim 10^4-10^5$. In this model the fractional outer gap size is proportional to $P^{-1/2}$. The predicted gamma-ray luminosity ($L_{\gamma}$) and the characteristic curvature photon energy ($E_c$) emitted from the outer gap are proportional to $B^2P^{-5/2}$ and $B^{3/4}P^{-1}$ respectively. This model also predicts that $L_{\gamma}$ and $E_c$ are related to the spin down power ($L_{sd}$) or the spin down age of pulsars ($\tau$) as $L_{\gamma} \propto L_{sd}^{5/8}$ or $L_{\gamma} \propto \tau^{-5/4}$, and $E_c \propto L_{sd}^{1/4}$ or $E_c \propto \tau^{-1/2}$ respectively.