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Last modified: 6 December 2023


Latest Updates

This document highlights important changes and additions to Sherpa functionality in the CIAO 4.16 Sherpa release.

Sherpa version for CIAO 4.16 was released on December 12, 2023. Sherpa in CIAO runs under Python 3.11, 3.10, 3.9, (when installed using the conda package manager) and Python 3.11 (when installed with ciao-install). The full list of the Sherpa updates is given in the 4.16.0 and 4.15.1 release notes on GitHub. The major updates were made to data filtering and grouping, addition of a new plotting backend, new plotting functions and bug fixes. The release highlights include:

  • Updated to version 12.13.1e of the XSPEC model library.

  • Fix an issue with the redshift parameter for XSPEC table models.

  • Allow XSPEC table models which include the ESCALE parameter.

  • Provide experimental support for writing out XSPEC table models.

Filtering and grouping

The grouping commands like group_counts and group_snr now default to only grouping within the noticed range of channels, which is a change in behaviour. The filter status is now reported for calls to the group commands and set_analysis, to follow the behavior of notice and ignore which were changed to report the filter status in CIAO 4.15.


Added support for use of arbitrary python functions when linking model parameters.

Data access
  • The save_arf and save_rmf calls have been added.

  • A number of changes hace been made to improve the output of the save_all command.

  • Routines have been added to convert an RMF to an image to help visualzie the instrument response (they have a similar capability to the rmfimg tool).

Random number generation

It is now easier to ensure that Sherpa is repeatable, taking advantage of the NumPy Random Number Generator along with the new set_rng and get_rng calls.

Plotting improvements

New plotting backend: Users can now choose between matplotlib and bokeh (experimental, users need to install the package).

A number of plot issues related to PHA data have been addressed.


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 4.16 and 4.15.1 release branches on GitHub.