FULL ELECTROMAGNETIC CASCADES IN SPIN-POWERED PULSARS

摘要

We simulate the full pair-photon cascade initiated by a single primary electron above the stellar surface of a normal spin-down-powered pulsar, using the Monte Carlo method. For a primary electron with a specified initial energy moving along a given field line, a cascade is initiated at the lower pair formation front. This cascade involves curvature radiation from the primary electron, conversion of photons emitted by the primary and secondary particles to electron-positron pairs, and subsequent quantum synchrotron radiation and inverse Compton scattering by the secondary pairs. Finally, high-energy photon and pair spectra are calculated. In our simulation, the space charge-limited flow model is incorporated, in which the acceleration gap is high above the stellar surface (about several stellar radii). However, we do not consider the exact acceleration in the gap; we just give the initial energy of the electron at the pair formation front and then trace the primary and secondary particles and photons emitted during the journey of those particles in the magnetosphere. Based on a two-dimensional picture and ignoring rotational effects, we calculate the resulting spectra for different pulsar parameters and find that the inverse Compton scattering component of the pairs can contribute significantly to the final spectrum below several MeV for a normal pulsar.