A Monte-Carlo Implementation of a Geodesic Integrator for Relativistic Radiative Transfer in Accreting Black Hole Systems

We describe the implementation of a relativistic geodesic integrator into a Monte-Carlo radia-
tive transfer code intended for computing the spectra produced from thermal emission in optically
thick accretion disks around a black hole. We first implemented the integrator and tested it by
computing geodesics in the Schwarzschild metric and demonstrated agreement with geodesics
computed by the relativistic radiative transfer code geokerr (Dexter & Agol 2009). We then im-
plemented the integrator as a module to transport photons in the existing Monte-Carlo radiation
transfer code mcgrid (Davis et al. 2009). We tested our newly implemented transport module
by computing transfer through a cylindrical grid geometry. Next, we demonstrated that it could
produce a black-body spectrum. Finally, we tested the code by transporting photons through a
transparent grid and compared the exit positions of the particles for different step sizes.