Last modified: December 2018

AHELP for CIAO 4.11 Sherpa v1


Context: models


comptonization of a seed spectrum. XSpec convolution model *Experimental*.


The SIMple Power Law model: An empirical model of Comptonization in which a fraction of the photons in an input seed spectrum is scattered into a power-law component (Steiner et al. 2009, PASP, 121, 1279). It is designed for use with soft thermal spectra that are not Compton thick and that have a photon index

Gamma > 1

Simpl offers the advantage of operating in a self-consistent manner, linking the seed spectrum to the generated power law. Compared to powerlaw, simpl gives equally-good fits while also employing just two parameters, and simpl has the virtue of eliminating the divergence of powerlaw at low energies. Because simple redistributes input photons to higher (and lower) energies, for detectors with limited response matrices (at high or low energies), or with poor resolution, the sampled energies should be extended to adequately cover the relevant energy range (for details and an example, see the appendix in Steiner et al. 2009). Please contact the CXC HelpDesk if you need to do this.

xssimpl Parameters

Number Name Description
1 Gamma The photon power law index
2 FracSctr The scattering fraction (between 0 and 1).
3 UpScOnly A flag to switch between up-scattering only (> 0) and both up- and down-scattering (<= 0).

Loading the X-Spec convolution models

Please see ahelp xsconvolve for information on how to load the model.


XSpec version

This information is taken from the XSpec User's Guide. Version 12.10.0e of the XSpec models is supplied with CIAO 4.11.


sherpa> from sherpa_contrib.xspec.xsconvolve import load_xssimpl
sherpa> load_xssimpl("smpl")
sherpa> set_source(smpl(xsapec.therm))
sherpa> smpl.upsconly = 1

The apec component is convolved by the simpl model, which is set to only use up-scattering.

About Contributed Software

This script is not an official part of the CIAO release but is made available as "contributed" software via the CIAO scripts page. Please see this page for installation instructions - such as how to ensure that the parameter file is available.


For a list of known bugs and issues with the XSPEC models, please visit the XSPEC bugs page.

See Also

list_model_components, list_models, load_xscflux, load_xsclumin, load_xscpflux, load_xsgsmooth, load_xsireflect, load_xskdblur, load_xskdblur2, load_xskerrconv, load_xslsmooth, load_xspartcov, load_xsrdblur, load_xsreflect, load_xsrfxconv, load_xsrgsxsrc, load_xsvashift, load_xsvmshift, load_xsxilconv, load_xszashift, load_xszmshift, models, tablemodel, xs, xsconvolve