Modeling of γ-ray Pulsar Light Curves from Force-Free Magnetosphere

Abstract

The Fermi LAT has recently discovered dozens of new gamma-ray pulsars, and is destined to revolutionize our knowledge of pulsar science. The gammaray pulsar light curves carry important information about pulsar magnetospheric structure, which has commonly been modeled as a vacuumdipole.We briefly review theoreticalmodels of gamma-ray pulsar light curves and point out their uncertainties due to the usage of vacuum field. We present the first results of pulsar high-energy light curve modeling using the more realistic force-free (FF) field taken from timedependent FF simulations.With the FF field, we find the conventional slot-gap (twopole caustic) and outer-gap models are no longer able to produce the commonly observed double-peak light curves. The most geometrically favored gamma-ray emission zone lies in a thin layer near the edge of the open flux tube. Emission from this “separatrix layer” generally produces two sharp peaks in the light curve, which are formed near and beyond the light cylinder.We show that most features and statistics from the currently available gamma-ray pulsar light curves can be well reproduced and explained in this framework. The location of this emission zone strongly suggests its association with the current sheet, thus calling for more detailed study of current sheet physics and particle acceleration.