Last modified: December 2023

AHELP for CIAO 4.16 Sherpa


Context: models


Summary of Sherpa models (excluding XSPEC).


The following table lists most of the models available within Sherpa. See "ahelp xs" for those models provided by XSPEC, "ahelp tablemodel" for table models, and "ahelp load_user_model" for user-supplied models, respectively.

One-dimensional Sherpa models

Model name Description
absorptionedge Optical model of an absorption edge.
absorptiongaussian Gaussian function for modeling absorption (equivalent width).
absorptionlorentz Lorentz function for modeling absorption (equivalent width).
absorptionvoigt This model has been replaced by Voigt1D
accretiondisk A model of emission due to an accretion disk.
atten Model the attenuation by the Inter-Stellar Medium (ISM).
bbody A one-dimensional Blackbody model.
bbodyfreq A one-dimensional Blackbody model (frequency).
beta1d One-dimensional beta model function.
blackbody Emission from a black body as a function of wavelength.
box1d One-dimensional box function.
bpl1d One-dimensional broken power-law function.
bremsstrahlung Bremsstrahlung emission.
brokenpowerlaw Broken power-law model.
ccm Galactic extinction: the Cardelli, Clayton, and Mathis model.
const1d A constant model for one-dimensional data.
cos One-dimensional cosine function.
delta1d One-dimensional delta function.
dered A de-reddening model.
edge Photoabsorption edge model.
emissiongaussian Gaussian function for modeling emission.
emissionlorentz Lorentz function for modeling emission.
emissionvoigt This model has been replaced by Voigt1D
erf One-dimensional error function.
erfc One-dimensional complementary error function.
exp One-dimensional exponential function.
exp10 One-dimensional exponential function, base 10.
fm UV extinction curve: Fitzpatrick and Massa 1988.
gauss1d One-dimensional gaussian function.
jdpileup A CCD pileup model for the ACIS detectors on Chandra.
linebroad A one-dimensional line-broadening profile.
lmc LMC extinction: the Howarth model.
log One-dimensional natural logarithm function.
log10 One-dimensional logarithm function, base 10.
logabsorption Gaussian function for modeling absorption (log of fwhm).
logemission Gaussian function for modeling emission (log of fwhm).
logparabola One-dimensional log-parabolic function.
lorentz1d One-dimensional normalized Lorentz model function.
normbeta1d One-dimensional normalized beta model function.
normgauss1d One-dimensional normalised gaussian function.
opticalgaussian Gaussian function for modeling absorption (optical depth).
poisson One-dimensional Poisson function.
polynom1d One-dimensional polynomial function of order 8.
polynomial Polynomial model of order 5.
powerlaw Power-law model.
powlaw1d One-dimensional power-law function.
pseudovoigt1d A weighted sum of a Gaussian and Lorentzian distribution.
recombination Optically-thin recombination continuum model.
scale1d A constant model for one-dimensional data.
schechter One-dimensional Schechter model function.
seaton Galactic extinction: the Seaton model from Synphot.
sin One-dimensional sine function.
sm Galactic extinction: the Savage & Mathis model.
smc SMC extinction: the Prevot et al. 1984 model.
sqrt One-dimensional square root function.
stephi1d One-dimensional step function.
steplo1d One-dimensional step function.
tan One-dimensional tan function.
voigt1d One dimensional Voigt profile.
xgal Extragalactic extinction: Calzetti, Kinney and Storchi-Bergmann

Two-dimensional Sherpa models

Model name Description
beta2d Two-dimensional beta model function.
box2d Two-dimensional box function.
const2d A constant model for two-dimensional data.
delta2d Two-dimensional delta function.
devaucouleurs2d Two-dimensional de Vaucouleurs model.
disk2d Two-dimensional uniform disk model.
gauss2d Two-dimensional gaussian function.
hubblereynolds Two-dimensional Hubble-Reynolds model.
lorentz2d Two-dimensional un-normalised Lorentz function.
normgauss2d Two-dimensional normalised gaussian function.
polynom2d Two-dimensional polynomial function.
scale2d A constant model for two-dimensional data.
sersic2d Two-dimensional Sersic model.
shell2d A homogenous spherical 3D shell projected onto 2D.
sigmagauss2d Two-dimensional gaussian function (varying sigma).

Are models evaluated at a point or across a bin?

The integration of models in Sherpa is controlled by an integration flag in each model structure. Refer to"ahelp integrate" for information on integrating model components.


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

See Also

list_model_components, list_models, tablemodel, xs