Pair production and gamma-ray emission over pulsar polar caps.

摘要

This dissertation discusses the creation of electron-positron cascades in the context of pulsar polar cap acceleration models, deriving several useful analytic and semi-analytic results for the spatial extent and energy response of the cascade. Such cascades are thought to be crucial for the operation of ratio pulsars. Instead of Monte Carlo simulations previously performed, I use an integro-differental equation which describes the development of the cascade's energy spectrum in one space dimension quite well, when it is compared to existing Monte Carlo models. I reduce this full equation to a single integral equation, from which can be derived useful results, such as the energy loss between successive generations of photons and the spectral index of the response.; Using this formalism, I calculate the height at which pair creation truncates the acceleration zone for the pulsars in the Princeton catalog. I find that for most low- and moderate-field pulsars, the height of the pair formation front and the final Lorentz factor of the primary beam is set by nonresonant inverse Compton scattering (NRICS), in the Klein-Nishina limit, rather than curvature emission or resonant inverse Compton scattering, as was previously thought.; The derived structure of the acceleration region naturally leads to predictions for the expected polar cap gamma-ray emission. I divide pulsars into several categories, based on which mechanism truncates the particle acceleration off the polar cap, and give estimates for the expected luminosity of each category.; Due to the effects of NRICS, the expected luminosity is lower than that predicted by previous models based on pure curvature emission. Even for the brightest pulsars, we find predicted luminosities too low to explain the EGRET pulsars, suggesting that the source of that emission is an outer-gap accelerator. The predicted polar cap luminosities are large enough, however, to be observable by upcoming γ-ray instruments, which provides a firm test for this theory. More sensitive observations should show the predicted narrow pulse shape of polar cap gamma-rays and the expected variation of luminosity with pulsar parameters.