Radiative Transfer in Obliquely Illuminated Accretion Disks

The illumination of an accretion disk around a black hole or neutron star bythe central compact object or the disk itself often determines its spectrum,stability, and dynamics. The transport of radiation within the disk is ingeneral a multi-dimensional, non-axisymmetric problem, which is challenging tosolve. Here, I present a method of decomposing the radiative transfer equationthat describes absorption, emission, and Compton scattering in an obliquelyilluminated disk into a set of four one-dimensional transfer equations. I showthat the exact calculation of the ionization balance and radiation heating ofthe accretion disk requires the solution of only one of the one-dimensionalequations, which can be solved using existing numerical methods. I present avariant of the Feautrier method for solving the full set of equations, whichaccounts for the fact that the scattering kernels in the individual transferequations are not forward-backward symmetric. I then apply this method incalculating the albedo of a cold, geometrically thin accretion disk.Comment: 16 pages, 3 figures; to appear in The Astrophysical Journa