Why We Should Kerr About the Dark Secrets of Relativistic Accretion Disks in Athena++

Monte Carlo numerical solutions to the radiation transfer equation in curved spacetime require both sampling of radiation-matter interactions and calculation of the null geodesics for photon trajectories. Our code, written in C++ using the Athena++ grid framework, integrates geodesics in general spacetimes, with a particular focus on Kerr metric of spinning black holes. Since our main intent is studying accretion disks around supermassive black holes, we include free-free absorption and emission along with polarized or unpolarized Compton scattering. After showing convergence and performance comparisons to other codes on test problems, we generate synthetic spectra from accretion disk models and simulations.