Simulation-based discrimination of Crab pulsar models with XL-Calibur

Abstract: Polarisation of X-ray light is being investigated with polarimeters to extend the borders of what can be observed. Distant compact objects, such as pulsars, that are to small on the sky to be analysed with imaging can be investigated by analysing the polarisation of the emitted light. This can reveal physics previously hidden by their small nature. There are many models that aim to describe the polarisation of these compact objects to make sense of what is measured. Two examples are the outer gap and two-pole caustic models. The X-ray polarimeter XL-Calibur is a balloon-borne telescope capable of detecting X-rays in the $15-80$ keV energy range. In this thesis details on the polarisation of light, how it can be measured and some principles of X-ray polarimetery is discussed. A new feature in the simulation of XL-Calibur in Geant4 is also described and used to investigate the possibility for XL-Calibur to distinguish between different Crab pulsar polarisation models at different signal rates. The results show that signal rates under 2 Hz yield insufficient data to distinguish between the two models using the measured polarisation fraction and angle. For greater signal rates XL-Calibur does in fact differentiate between the models correctly. New methods for the statistical analysis of data can be explored to allow more data to be salvaged, even for low signal rates. The derivation of polarisation parameters is fixed through Stokes parameters in this thesis.