Skip to the navigation links
Last modified: 7 December 2022


Latest Updates

This document highlights important changes and additions to Sherpa functionality in the CIAO 4.15 Sherpa release.

Sherpa version for CIAO 4.15 was released on December 13, 2022. Sherpa in CIAO runs under Python 3.10, 3.9, 3.8 (when installed using the conda package manager) and Python 3.9 (when installed with ciao-install). The full list of the Sherpa updates is given in the 4.15.0 and 4.14.1 release notes on GitHub. The major updates were made to data validation, plotting backend and infrastructure. The release highlights related to UI include:


Updated to version 12.12.1 of the XSPEC model library.

The chi2xspecvar statistics in fitting PHA data now matches XSPEC when the background is subtracted and the source or background group contains 0 counts.


Models can now be frozen or thawed when accessing the model objects directly.

Filtering and grouping

Change to the filter is reported to the screen in the interactive session when using notice or ignore - including the variants notice_id and ignore2d

Plotting improvements

CIAO 4.15 continued the improvements to the plotting functionality, and includes internal changes to the plotting code and documentation.


The Sherpa ahelp files have been updated to match the Python docstrings. Each command has its own ahelp file, rather than combining multiple commands into a single file.


Help can be found either via Python's native help function (that is, Python docstrings), or with the ahelp command (which can be used from both the command line and within the Sherpa interactive environment.

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

A standalone the Sherpa documentation provides on-line access to the Python docstrings, as well as general documentation on how to use Sherpa. It is aimed at users who want to use the more object-orientated interface provided by Sherpa rather than the functions from the sherpa.astro.ui module documented on this site, as well as not being tailored to CIAO users, but it is useful for the more advanced Sherpa users who want to use Sherpa in complex Python pipelines.

Bug Fixes

A full list of the bug fixes can be found by viewing the changes made to the 4.15 and 4.14.1 release branches on GitHub.