Monte Carlo Simulations of Compton Polarization in Astrophysical Sources

Abstract

The description of many high-energy astrophysical sources relies on the production of relativistic jets that are accompanied by the acceleration of particles up to very high energies, and the production of non-thermal radiation (e.g. active galactic nuclei (AGNs), γ-ray bursts (GRBs), X-ray binaries (XRBs), and γ-ray binaries). The radiation from these jet-like sources is characterized by their spectral energy distributions (SEDs), which can be modelled in many different ways, all of which are consistent with the spectral shape of the SED. Discriminating between different models is one of the main objectives in the field of high-energy astrophysics. Compared with the orientation of the relativistic jet, the polarization from the high-energy radiation in astrophysical sources adds crucial knowledge of the jet-physics and jet-formation models. Even though high-energy polarization has remained largely unexplored, the future prospects of detecting polarization in X-rays/soft γ-rays from many astrophysical sources have renewed interest in model predictions of polarization in the high-energy regime. Linear polarization arises from synchrotron radiation of relativistic charged particles in ordered magnetic fields, while Compton scattering off relativistic electrons will reduce the degree of polarization to about half of the target photon polarization. In a model where a thermal and a non-thermal particle distribution scatters an external radiation field, hard X-ray/γ-ray radiation results form relativistic electrons, and the radiation is predicted to be unpolarized. Contrarily, Ultraviolet (UV)/X-ray radiation, resulting from scattering by thermal electrons, is predicted to be polarized. This dissertation describes the development of a Monte Carlo code to study the degree and orientation of Compton polarization in the high-energy regime of jet-like astrophysical sources.