CIAO's modeling and fitting package

Sherpa is the CIAO modeling and fitting application. It enables the user to construct complex models from simple definitions and fit those models to data, using a variety of statistics and optimization methods.

Modern data analysis requires a flexible modeling and fitting system. The new Sherpa infrastructure greatly enhances the default Sherpa functions, and provides users with an environment for developing complex and sophisticated analysis.

Sherpa is designed for use in a variety of modes: as a user-interactive application and in batch mode. Sherpa is an importable module for scripting languages (Python or S-Lang) and is available as a C/C++ library for software developers. In addition, users may write their own Python and S-Lang scripts for use in Sherpa; refer to the page Should I Use Sherpa in Python or S-Lang? page for help in deciding which language to use.

The About the Sherpa Release page outlines new features and provides a summary of missing items with respect to Sherpa 3.4. For the most recent changes to Sherpa functionality, see the Latest Updates page. Please send feedback and questions on Sherpa to the Helpdesk.

The CXC is committed to helping Sherpa users transition to new syntax as smoothly as possible. If you have existing Sherpa scripts or save files, submit them to us via the CXC Helpdesk and we will provide the CIAO/Sherpa 4.1 syntax to you.

Citing Sherpa in a Publication

If you are writing a paper and would like to cite Sherpa, we recommend the following paper:

\bibitem[Freeman et al.(2001)]{2001SPIE.4477...76F} Freeman, P., Doe, S., 
\& Siemiginowska, A.\ 2001, \procspie, 4477, 76

The specific version of CIAO and CALDB (if applicable) used for the analysis should be mentioned as well.

A reference for the Python interface to Sherpa is also available:

\bibitem[Doe et al.(2007)]{2007ASPC..376..543D} Doe, S., et al.\ 2007, 
Astronomical Data Analysis Software and Systems XVI, 376, 543

Further guidelines are available from the Acknowledgment of Use of Chandra Resources.