Geometric modelling of radio and [gamma]-ray light curves of 6 Fermi LAT pulsars

Abstract

The launch of the Large Area Telescope (LAT), on board the Fermi spacecraft, has led to an astounding increase in the number of known y-ray pulsars. This wealth of new data has generated renewed interest in the field of pulsar astrophysics, with many of the established geometric models for y-ray emission coming under fresh scrutiny. In this work the outer gap (OG) and two-pole caustic (TPC) geometric -ray models are employed alongside a simple empirical radio model to obtain best-fit light curves by eye for six single-peak Fermi LAT pulsars first reported by Weltevrede et al. (2010). These best-fit solutions aim to reproduce both the shapes of the radio and y-ray light curves, and the radio-to- phase lag. A parameter study of the geometric models is also conducted, and the increased qualitative understanding of these models thus gained is then employed to obtain the best fits possible. The combination of radio and -ray models is found to be remarkably powerful in constraining the values of the geometric parameters of the individual pulsars: the inclination and observer angles. Generally the constraints implied by the radio model act perpendicularly to those implied by the y-ray models, thus yielding smaller solution contours. The constraints on the geometric parameters obtained for the six Fermi LAT pulsars in question agree quite well with those obtained by Weltevrede et al. (2010). This agreement is remarkable considering that the approach employed in this study is independent from the one employed by Weltevrede et al. (2010). The errors obtained in this study on the values of the inclination angle for each pulsar are generally smaller than those obtained by Weltevrede et al. (2010). As a secondary result, the value of the flux correction factor, which is a measure of how well the observed y-ray energy flux of the pulsar correlates with the overall y-ray energy flux, is constrained for each pulsar.