Last modified: December 2023

AHELP for CIAO 4.16 Sherpa


Context: models


The XSPEC zkerrbb model: multi-temperature blackbody model for thin accretion disk around a Kerr black hole.



The xszkerrbb model is an additive model component.


The model is described at [1] .


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

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

   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.eta      frozen            0            0            1           
   mdl.a        thawed          0.5        -0.99       0.9999           
   mdl.i        frozen           30            0           85        deg
   mdl.Mbh      thawed        1e+07            3        1e+10      M_sun
   mdl.Mdd      thawed            1        1e-05       100000       M0yr
   mdl.z        frozen         0.01            0           10           
   mdl.fcol     frozen            2         -100          100           
   mdl.rflag    frozen            1 -3.40282e+38  3.40282e+38           
   mdl.lflag    frozen            1 -3.40282e+38  3.40282e+38           
   mdl.norm     thawed            1            0        1e+24           


The attributes for this object are:

Attribute Definition
eta The ratio of the disk power produced by a torque at the disk inner boundary to the disk power arising from accretion. See [1] for more details.
a The specific angular momentum of the black hole in units of the black hole mass M (when G=c=1). It should be in the range [-1, 1).
i The disk inclination angle, in degrees. A face-on disk has i=0. It must be less than or equal to 85 degrees.
Mbh The mass of the black hole, in solar masses.
Mdd The "effective" mass accretion rate in units of M_solar/year. See [1] for more details.
z The redshift of the black hole
fcol The spectral hardening factor, Tcol/Teff. See [1] for more details.
rflag A flag to switch on or off the effect of self irradiation: when greater than zero the self irradition is included, otherwise it is not. This parameter can not be thawed.
lflag A flag to switch on or off the effect of limb darkening: when greater than zero the disk emission is assumed to be limb darkened, otherwise it is isotropic. This parameter can not be thawed.
norm The normalization of the model. It should be fixed to 1 if the inclination, mass, and distance are frozen.


Changes in CIAO

Changed in CIAO 4.14

The fcol parameter was incorrectly labelled as hd: both names can be used to access this parameter.

The default a, Mbh, fcol, and lflag parameter values have changed from 0, 1, 1.7, and 0 to 0.5, 1e7, 2.0, and 1 to match XSPEC.

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.

See Also