Exploiting Morphological Data from Pulsar Wind Nebulae via a Spatio-Temporal Leptonic Transport Code

Abstract

The next era of ground-based Cherenkov telescope development will see a great increase in both quantity and quality of $\gamma$-ray morphological data. This initiated the development of a spatio-temporal leptonic transport code to model pulsar wind nebulae. We present results from this code that predicts the evolution of the leptonic particle spectrum and radiation at different radii in a spherically-symmetric source. We simultaneously fit the overall broadband spectral energy distribution, the surface brightness profile and the X-ray photon index vs.\ radius for PWN 3C~58, PWN G21.5$-$0.9 and PWN G0.9+0.1. Such concurrent fitting of disparate data sets is non-trivial and we thus investigate the utility of different goodness-of-fit statistics, specifically the traditional $\chi^2$ test statistic and a newly developed scaled-flux-normalised test statistic to obtain best-fit parameters. We find reasonable fits to the spatial and spectral data of all three sources, but note some remaining degeneracies that will have to be broken by future observations.