1 research outputs found
Ray-Tracing Based Polarized Radiative Transfer in General Spacetimes
This thesis presents a ray-tracing based method for performing polarized radiative transfer in
arbitrary spacetimes and a numerical implementation of said method. This method correctly
accounts for general relativistic effects on the propagation of radiation, and the polarized im-
ages and spectra it produces can be directly compared with observations. Thus it is well suited
for studying systems where relativistic effects are significant, such as compact astrophysical objects.
The ray-tracing method is based on several approximations, which are discussed in depth.
The most important one of these is the geometric optics approximation, which is derived starting
from Maxwell’s equations. In the geometric optics approximation, high frequency radiation is
described as amplitudes or intensities which are propagated along geodesic rays. Additional
assumptions about the properties of the radiation field allow describing it and its interaction with
matter using the formalism of kinetic theory, which leads to a simple transfer equation along rays.
This transfer equation is valid in arbitrary spacetimes, and forms the basis for the ray-tracing
method.
The ray-tracing method presented in this work and various similar methods described in
the literature are not suited for analytic computations using realistic models. Instead numerical
methods are needed. Such numerical methods are implemented in a general fashion in the
Arcmancer library (paper in preparation), of which large parts were implemented as a part of
this work. The implementation details of Arcmancer are described and its features are compared
to those available in other similar codes. Tests of the accuracy of the numerical methods as
well as example applications are also presented, including a novel computation of a gravitational
lensing event in a binary black hole system. The implementation is found to be correct and easily
applicable to a variety of problems