  Interstellar extinction includes both absorption and scattering of photons
from interstellar gas and dust grains, and it has the effect of altering a
source's spectrum and its total observed intensity. However, while multiple
absorption models exist, there are no useful scattering models in standard
X-ray spectrum fitting tools, such as XSPEC. Nonetheless, X-ray halos, created
by scattering from dust grains, are detected around even moderately absorbed
sources and the impact on an observed source spectrum can be significant, if
modest, compared to direct absorption. By convolving the scattering cross
section with dust models, we have created a spectral model as a function of
energy, type of dust, and extraction region that can be used with models of
direct absorption. This will ensure the extinction model is consistent and
enable direct connections to be made between a source's X-ray spectral fits and
its UV/optical extinction.
