Last modified: December 2023

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AHELP for CIAO 4.16 Sherpa


Context: models


A one-dimensional Blackbody model.




A model representing the ideal blackbody function. It can be used when the independent axis is in energy or wavelength space.


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

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

   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----    frozen            0            0            1 0 - energy | 1 - wave
   mdl.kT       thawed            1          0.1         1000        keV
   mdl.ampl     thawed            1        1e-20        1e+20           


The attributes for this object are:

Attribute Definition
space Switch to select whether the independent axis is energy or wavelength. This parameter is not fit ( alwaysfrozen is set), and should be set to either 0, when the independent axis is energy with units of keV, or 1 when the axis is wavelength with units of Angstrom.
kT The temperature if the blackbody, in keV.
ampl The amplitude of the blackbody component.


The blackbody emission is calculated as a function of energy using the expression:

f(E) = ampl * E^2 / (exp(E / kT) - 1)

where E is the photon energy, and kT is the blackbody temperature (both in keV). The amplitude, ampl, is related to the ratio of source radius to distance by:

ampl = (2 * pi / (c^2 * h^3)) (R / d)^2
     = 9.884 x 10^31 (R / d)^2

with Planck's constant (h) specified in keV-s and the speed of light (c) specified in cm/s, and with R and d representing the radius of, and distance to, the source respectively.

There are two conditions when the above equation is not used:


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

See Also