Modeling gamma-ray light curves with more realistic pulsar magnetospheres

Abstract

We study the gamma-ray emission patterns and light curves in dissipative pulsar magnetospheres. We produce the gamma-ray light curves by using the geometric method and the particle trajectory method. For the geometric method, assuming the gamma-ray emission originates in a finite-width layer along the last closed lines, we generate the gamma-ray light curves based on the uniform emissivity along the magnetic field lines in the comoving frame (CF). For the particle trajectory method, we consider the spatial distribution of conductivity $\sigma$ by assuming a very high conductivity within the light cylinder and a finite conductivity outside the light cylinder (LC). Assuming that all the $\gamma$-ray emission originates in the outer magnetosphere outside the LC, we generate the gamma-ray light curves by computing realistic particle trajectories and Lorentz factors, taking into account both the accelerating electric field and curvature radiation loss. Further, we compare the modeling light curves to the observed light curves at $>0.1\, \rm GeV$ energies for Vela pulsar. Our results show that the magnetosphere with the low $\sigma$ value is more preferred for the geometric method. However, the magnetosphere with a near force-free regime within the LC and a high $\sigma$ value outside the LC is more favored for the particle trajectory method. It is noted that the particle trajectory method uses the parallel electric fields that are self-consistent with the magnetic fields of the magnetosphere. We suggest that the results from the particle trajectory method are more supported on the physical ground.