Last modified: December 2018

URL: http://cxc.harvard.edu/sherpa/ahelp/logemission.html
Jump to: Description · Example · ATTRIBUTES · Notes · Bugs · See Also


AHELP for CIAO 4.11 Sherpa v1

logemission

Context: models

Synopsis

Gaussian function for modeling emission (log of fwhm).

Syntax

logemission

Description

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


Example

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

Create a component of the logemission 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

This is a hidden parameter and is unused by the model.

Notes

The functional form of the model for points is:

f(x) = fmax * (x / pos)^arg                    if x <= pos

       fmax * (x / pos)^(-alpha)               otherwise

arg = log(2) / log(1 + 0.5 * fwhm / c)

arg1 = log(2) / log(1 + 0.5 * skew * fwhm / c)

alpha = arg                                    if skew == 1

      = arg1                                   otherwise

fmax = (arg - 1) * flux / (2 * pos)            if skew == 1

     = (arg - 1) * flux / (pos * (1 + (arg - 1) / (arg1 - 1)))

                                               otherwise

c = 2.9979e5

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


Bugs

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

See Also

models
emissiongaussian, logabsorption