Last modified: December 2023

AHELP for CIAO 4.16 Sherpa


Context: models


The XSPEC compPS model: Comptonization, Poutanen & Svenson.



The xscompps model is an additive model component.


The model is described at [1] .

Deprecated in Sherpa 4.10.0

The tauy and hrcyl parameters have been renamed to tau_y and hovr_cyl respectively to match the XSPEC definition. The names tauy and hrcyl can still be used to access the parameters, but they will be removed in a future release.


>>> create_model_component("xscompps", "mdl")
>>> print(mdl)

Create a component of the xscompps model and display its default parameters. The output is:

   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.kTe      thawed          100           20       100000        keV
   mdl.EleIndex frozen            2            0            5           
   mdl.Gmin     frozen           -1           -1           10           
   mdl.Gmax     frozen         1000           10        10000           
   mdl.kTbb     frozen          0.1        0.001           10        keV
   mdl.tau_y    thawed            1         0.05            3           
   mdl.geom     frozen            0           -5            4           
   mdl.HovR_cyl frozen            1          0.5            2           
   mdl.cosIncl  frozen          0.5         0.05         0.95           
   mdl.cov_frac frozen            1            0            1           
   mdl.rel_refl frozen            0            0        10000           
   mdl.Fe_ab_re frozen            1          0.1           10           
   mdl.Me_ab    frozen            1          0.1           10           
   mdl.xi       frozen            0            0       100000           
   mdl.Tdisk    frozen        1e+06        10000        1e+06          K
   mdl.Betor10  frozen          -10          -10           10           
   mdl.Rin      frozen           10        6.001        10000         Rs
   mdl.Rout     frozen         1000            0        1e+06         Rs
   mdl.redshift frozen            0       -0.999           10           
   mdl.norm     thawed            1            0        1e+24           


The attributes for this object are:

Attribute Definition
kTe The electron temperature in keV.
EleIndex The electron power-law index.
Gmin The minimum Lorentz factor gamma.
GMax The maximum Lorentz factor gamma: see [1] for more details.
kTbb The temperature of the soft photons, in keV.
tau_y The vertical optical depth of the corona: see [1] for more details.
geom The geometry to use; see [1] for more details.
HovR_cyl The value of H/R, when a cylinder geometry is used (abs(geom) = 2).
cosIncl The cosine of the inclination angle.
cov_frac The covering fraction of the cold clouds (only used when abs(geom) < 4).
rel_refl The amount of reflection (Omega / (2 pi))
Fe_ab_re The iron abundance, in units of solar.
Me_ab The abundance of heavy elements, in units of solar.
xi The disk ionization parameter.
Tdisk The disk temperature for reflection, in K.
Betor10 The reflection emissivity law: see [1] for more details.
Rin The inner radius of the disk in Schwarzschild units.
Rout The outer radius of the disk in Schwarzschild units.
redshift The redshift of the source.
norm The normalization of the model.


The precision of the numerical integration can be changed by using the set_xsxset function to set the value of the COMPPS_PRECISION keyword, which defines the fractional precision. The default is 0.01 (1%).


XSPEC version

CIAO 4.16 comes with support for version 12.13.1e of the XSPEC models. This can be checked with the following:

% python -c 'from sherpa.astro import xspec;


See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.