Gamma-ray emission and pair creation of outer gap

Abstract

In this talk we use a simple two dimensional outer gap model, which consists of a primary acceleration region plus a screening region, to calculate the theoretical curvature radiation spectrum. We find that the observed spectra of all mature pulsars detected by Fermi can be explained in terms of three independent gap parameters,i.e. the gap current in the primary accelerator, the outer gap size and the gap ratio between the primary region and the total gap size. The fitting results indicate that (1)the current in primary region is only 10%of Goldreich-Julian current, which ensures the production of multi-GeV photons fromthe gap and (2)the gamma-ray power of pulsars is a broken power law of spin-down power, which suggests that there are two gap closure mechanisms.We next examine two possible pair creation processes, i.e. photon-photon pair creation and magnetic pair creation, we find that the former should be dominated for $L_{sd}<10^{36}{\rm erg/s}$ and the latter is more important for $L_{sd}<10^{36}{\rm erg/s}$. If the magnetic pair creation is the gap closure mechanism we predict that the gamma-ray luminosity $\left({\rm L}_{\gamma}\right)$ and the cut-off energy of the spectrum (E _c ) are given by $L_{\gamma}\alpha {L_{sd}^{5/8}}$ and $E_{c}\alpha {L_{sd}^{1/4}}$ respectively.