Last modified: December 2018

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


AHELP for CIAO 4.11 Sherpa v1

edge

Context: models

Synopsis

Photoabsorption edge model.

Syntax

edge

Description

This model can be used when the independent axis is in energy or wavelength space.


Example

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

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

mdl
   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.space    thawed            0            0            1 0 - energy | 1 - wave
   mdl.thresh   thawed            1            0  3.40282e+38           
   mdl.abs      thawed            1            0  3.40282e+38           

ATTRIBUTES

The attributes for this object are:

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.

thresh

The edge position (in energy or wavelength units matching the data grid).

abs

The absorption coefficient.

Notes

A phenomenological photoabsorption edge model as a function of energy:

f(x) = exp(-abs * (x / thresh)^-3)   if x >= thresh

     = 1.0                           otherwise

or, as a function of wavelength:

f(x) = exp(-abs * (x / thresh)^3)    if x <= thresh

     = 1.0                           otherwise

Bugs

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