Chandra X-Ray Observatory
Skip to the navigation links
Last modified: 10 April 2018


Latest Updates

This document highlights important changes and additions to Sherpa functionality in the CIAO 4.10 Sherpa release.

Latest Version

Sherpa version for CIAO 4.10 was released on April 18, 2018. Sherpa runs under Python 2.7, 3.5 and 3.6. The major updates include: XSPEC models version 12.9.1n and use of aliases for the parameter names, and consistent parameter limits; for advanced users who build Sherpa from source, multiple versions of XSPEC models are now supported, through optional models and version-dependent low-level function calls; Sherpa has been tested against XSPEC 12.9.0i, 12.9.0o, and 12.9.1n. There are also several bug fixes related to the support of instrumental responses, including improved support of the XMM and Swift responses; a bug fix in the user statistics, load_user_stat; improvements to the Python 3 compatibility, more robust usage of the numpy API, and several other minor bug fixes and new tests. CIAO release is based on the GitHub-developed version of Sherpa. Please consider contributing to Sherpa development, whether by adding code, fixing bugs, or changing documentation.

CIAO 4.10 Updates to Sherpa Functionality

XSPEC Models

The XSPEC model library has been updated to version 12.9.1n from 12.9.0d used in CIAO 4.9. The nlapec model is now included, it can be also emulated by taking advantage of the new APECNOLINES xset setting:

sherpa> set_source( * xsapec.src)
sherpa> set_xsxset('APECNOLINES', 'on')

The parameter names, default values and limits have been updated to match the changes made by XSPEC.

Sherpa now supports multiple versions of the XSPEC models from the 12.9.0 and 12.9.1 series. Some models recommend using the C-style interface over the older FORTRAN one, which may also resolve some memory access issues. For CIAO 4.10 users this means the interfaces to XSPEC models have been updated to the 12.9.1n versions. For standalone Sherpa users this means they can build and run Sherpa against a larger range of XSPEC versions, and Sherpa will pick the XSPEC low level model function accordingly. Sherpa has been tested against the following versions 12.9.0i, 12.9.0o, and 12.9.1n.

The 14 models that have been changed are: xsapec, xsbapec, xsbvapec, xsbvvapec, xsgaussian, xslorentz, xsmeka, xsmekal, xsraymond, xsvapec, xsvmeka, xsvmekal, xsvraymond, and xsvvapec.

New models in XSPEC 12.9.1: xsbvtapec, xsbvvtapec, xstapec, xsvtapec, xsvvtapec, xscarbatm, xshatm, xsismabs, xsslimbh, xssnapec, xsTBfeo, xsTBgas, xsTBpcf, xsTBrel, xsvoigt, xsxscat .

The Si and S elemental parameters for the xsismabs model have been renamed from the XSPEC version since they are not unique using the caseinsensitive matching used by Sherpa: so SI, SII, SIII and SiI, SiII, SiIII have been renamed S_I, S_II, S_III and Si_I, Si_II, and Si_III respectively.


The bug in user statistic - created with the load_user_stat command - has been fixed. The user statistics has access to the background component of a data set.


The top-level functions - namely those in the sherpa.astro.ui and sherpa.ui modules - have had their Python docstrings updated to reflect the current state of the ahelp files and to follow the NumPy docstring convention. These Python docstrings are now available from the Sherpa application via the help function (previously the text was replaced by a comment to use the ahelp function). The ahelp files are still provided in this release.

If you spot any errors, or missing information, in the docstrings, please submit a pull request to fix it or report the problem.

Bug Fixes

A full list of the bug fixes can be found on the CIAO 4.10 release notes page, or by viewing the changes made to the 4.10 release branch on GitHub.

Last modified: 10 April 2018
Smithsonian Institute Smithsonian Institute

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA.   Email: Smithsonian Institution, Copyright © 1998-2017. All rights reserved.