Last modified: December 2018

URL: http://cxc.harvard.edu/sherpa/ahelp/emissiongaussian.html
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AHELP for CIAO 4.11 Sherpa v1

emissiongaussian

Context: models

Synopsis

Gaussian function for modeling emission.

Syntax

emissiongaussian

Description

It is for use when the independent axis is in Angstroms.


Example

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

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

mdl
   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.fwhm     thawed          100  1.17549e-38  3.40282e+38       km/s
   mdl.pos      frozen         5000  1.17549e-38  3.40282e+38  angstroms
   mdl.flux     thawed            1 -3.40282e+38  3.40282e+38           
   mdl.skew     frozen            1  1.17549e-38  3.40282e+38           

ATTRIBUTES

The attributes for this object are:

fwhm

The full-width half-maximum of the model in km/s.

pos

The center of the gaussian, in Angstroms.

flux

The normalisation of the gaussian.

skew

The skew of the gaussian.

limit

The model is only evaluated for points that lie within limit sigma of pos. It is a hidden parameter, with a default value of 4.

Notes

The functional form of the model for points is:

f(x) = flux * exp(-0.5 * d(x)^2) / s2   if skew = 1

     = 2 * flux * exp(-0.5 * d2(x)^2) / (s2 * (1 + skew))

                                        otherwise

d(x) = (x - pos) / s

d2(x) = d(x)                  if x <= pos

      = d(x) / skew           otherwise

s2 = 2.50662828 * s

s = pos * fwhm / (2.9979e5 * 2.354820044)

and for integrated data sets the low-edge of the grid is used.

The calculation is only done for those points that are in the range:

|x - pos| < limit * sigma

Outside this range the model is set to 0.


Bugs

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

See Also

models
absorptiongaussian, emissionlorentz, emissionvoigt, logemission