Modeling of the X-ray Flux and Polarization Energy Spectra of Black Hole X-Ray Binaries with the KerrC Code

Abstract

In this chapter, we introduce the kerrC model, an advanced framework designed for the analysis of combined spectral and polarimetric X-ray emission from black hole systems. The model is built upon an extensive dataset of ray-tracing Monte Carlo simulations that compute the radiative transfer of X-rays in the strongly curved spacetime near the event horizon of a Kerr black hole. These simulations incorporate thermal seed emission from a geometrically thin, optically thick accretion disk, along with the subsequent Comptonization processes within a hot corona of variable geometry and physical properties. Crucially, the reflection of both primary disk and Comptonized photons is treated self-consistently utilizing the xillver reflection tables, and the polarization 4-vectors of the photons are rigorously transported throughout the simulation to preserve full polarization information. The code tracks photons forward in time, allowing for multiple photon scatterings in the corona and off the accretion disk. We detail the underlying mechanics of the ray-tracing simulations and the fitting models, and discuss the applications of kerrC in leveraging X-ray polarization observations to constrain black hole spin and coronal geometry.