This model describes X-ray transmission of an isotropic source of
photons located at the center of a uniform, spherical distribution
of matter, correctly taking into account Compton scattering.
The model can be used for radial column densities up to
cm
.
The valid energy range for which data can be modeled is between
10 and 18.5 keV, depending on the column density. Details of the
physics of the model, the approximations used and further details on
the regimes of validity can be found in Yaqoob (1997; ApJ, 479, 184).
In this particular incarnation, the initial spectrum is a power law
modified by a high-energy exponential cut-off above a certain
threshold energy.
Also, to improve the speed, a FAST option is available in which a full integration over the input spectrum is replaced by a simple mean energy shift for each bin. This option is obtained by setting parameter 9 to a value of 1 or greater and MUST BE FIXED. Further, for single-scattering albedos less than ACRIT (i.e. parameter 8) energy shifts are neglected altogether. The recommended value is ACRIT=0.1 which corresponds to about 4 keV for cosmic abundances and is more than adequate for ASCA data.
Note that for column
densities in the range cm
, the maximum number of
scatterings which need be considered for convergence of the spectrum
of better than 1% is between 1 and 5. For columns as high as
, the maximum number of scatterings which need be
considered for the same level of convergence is 12. **NOTE THAT
NMAX MUST BE FROZEN **
par1 = Column density in unitscm
.
par2 = Maximum number of scatterings to consider.
par3 = Iron abundance.
par4 = Iron K edge energy.
par5 = Power-law photon index.
par6 = High-energy cut-off threshold energy.
par7 = High-energy cut-off e-folding energy.
par8 = Critical albedo for switching to elastic scattering.
par9 = If par9.ge.1 uses mean energy shift, not integration.
par8 = Source redshift.