Radiation transfer of emission lines in curved space-time

Abstract

We present a general formulation for ray-tracing calculations in curved space-time. The formulation takes full account of relativistic effects in the photon transport and the relative motions of the emitters and the light-of-sight absorbing material. We apply the formulation to calculate the emission from accretion disks and tori around rotating black holes. In our model the emission lines and continuum originate from an accretion disk or torus, and the motion of the emitters in the disk/torus is determined by the gravity of the black hole and the space-time structure near the black hole. The line-of-sight absorbing medium is comprised of cold absorbing cloudlets. These cloudlets are kinematically hot, with their velocity dispersion determined by the local virial temperature. The emission from the accretion disk/torus is resonantly absorbed/scattered. Our calculations demonstrate that line-of-sight absorption significantly modifies the profiles of lines from the accretion disks. It is often difficult to disentangle absorption effects from other geometrical and kinematics effects, such as the viewing inclination and the spin of the black hole. Our calculations also show that emission lines from accretion tori and from thin accretion disks differ substantially. Large geometrical obscuration could occur in tori, and as a consequence lines from tori generally have much weaker redshift wings at large viewing inclination angles. Moreover, the blue peak is truncated.