  Super Soft X-ray Sources (SSS) are white dwarf (WD) binaries that radiate
almost entirely below $\sim$1~keV. Their X-ray spectra are often complex when
viewed with the X-ray grating spectrometers, where numerous emission and
absorption features are intermingled and hard to separate. The absorption
features are mostly from the WD atmosphere, for which radiative transfer models
have been constructed. The emission features are from the corona surrounding
the WD atmosphere, in which incident emission from the WD surface is
reprocessed. Modeling the corona requires different solvers and assumptions for
the radiative transfer, which is yet to be achieved. We chose CAL87, a SSS in
the Large Magellanic Cloud, which exhibits emission-dominated spectra from the
corona as the WD atmosphere emission is assumed to be completely blocked by the
accretion disk. We constructed a radiative transfer model for the corona using
the two radiative transfer codes; xstar for a one-dimensional two-stream solver
and MONACO for a three-dimensional Monte Carlo solver. We identified their
differences and limitations in comparison to the spectra taken with the
Reflection Grating Spectrometer onboard the XMM-Newton satellite. We finally
obtained a sufficiently good spectral model of CAL87 based on the radiative
transfer of the corona plus an additional collisionally ionized plasma. In the
coming X-ray microcalorimeter era, it will be required to interpret spectra
based on radiative transfer in a wider range of sources than what is presented
here.
