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Last modified: 28 January 2019


CIAO is the software package developed by the Chandra X-Ray Center for analysing data from the Chandra X-ray Telescope. It can also be used with data from other Astronomical observatories, whether ground or space based.


Install CIAO 4.11
& CALDB 4.8.2

Read the CIAO 4.11 release notes for detailed information on this release, including How CALDB 4.8.2 Affects Your Analysis.

Does CIAO run on my operating system?

What are the requirements for running CIAO?

How do I install Python packages into CIAO? [New] (13 Dec 2018)

Note: CIAO 4.11 uses Python 3.5. Python 2.7 in the scientific-software ecosystem is coming to an end and is no longer supported by CIAO.

What has changed?

Has there been a new release of CIAO, the contributed scripts, or the CALDB?

What's New

"Watch Out" List

Version History

CIAO Release Notes

CALDB Release Notes

Subscribe to the CIAO News RSS feed

Where should I begin?

Useful links for those people who have never used CIAO before.

Welcome to CIAO
Introduction to the Tools & Applications

Quick Start Guide

Download CIAO 4.11
Installing CIAO 4.11 thread

Introductory Science Threads
All CIAO Threads

Analysis Guides

I need help!

For anyone having trouble using CIAO or analysing Chandra data.

CIAO Software Help Pages

Frequently Asked Questions (FAQ)

Known CIAO Bugs and Tool Caveats

If the above links do not help you, then please contact the CXC Helpdesk. To help us help you, please include, where appropriate: the CIAO version (ciaover -v), operating system, screen output (in a text format where possible), and information on what you were trying to do.

Please, if at all possible, send in the actual text input and output rather than a screen shot of the terminal window.

I need more!

For the expert CIAO user or person who needs more detailed information.

Why Topics


Understanding the Chandra PSF.

Galleries (Tips & Tricks): CIAO; Sherpa; ChIPS.

The Chandra Instrument Calibration pages.

Using Python with CIAO [Updated] (13 Dec 2018)

Citing CIAO

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

CIAO: Chandra's data analysis system (ADS, PS)
Fruscione et al. 2006, SPIE Proc. 6270, 62701V, D.R. Silvia & R.E. Doxsey, eds.

\bibitem[Fruscione et al.(2006)]{2006SPIE.6270E..60F} Fruscione, A., et al.\ 2006, \procspie, 6270

The specific version of CIAO and CALDB used for the analysis should be mentioned.

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