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Last modified: 15 November 2022


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 4.12.1 & CALDB 4.10.2


Install with conda

Read the CIAO 4.12.1 release notes for detailed information on this release, including How CALDB 4.10.2 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?

Note that CIAO is packaged with Python 3.5 when using ciao-install, and with your choice of Python 3.7, 3.6, or 3.5 when using the conda installation method.

What has changed?

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

What's New

"Watch Out" List

How do I update CIAO?

Version History: CIAO; Scripts & Modules.

Release Notes: CIAO; CALDB.

Note that CIAO 4.12 is the first release which has support for installation via conda (for Python versions 3.7, 3.6, and 3.5), and is also the first release without ChIPS. Please see the ChIPS to Matplotlib conversion guide for help.

Subscribe to the CIAO News RSS feed

Where should I begin?

For those new to X-ray astronomy and data analysis

An X-ray Data Primer: What I Wish I Knew when Starting X-Ray Astronomy

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

Welcome to CIAO
Introduction to the Tools & Applications

Quick Start Guide

Download CIAO 4.12.1
Installing CIAO 4.12.1 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 include the actual text input and output (e.g. using copy and paste). Do not send in screen shots of the terminal window, as they make it much harder to identify and track down the problem.

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.

The Chandra Instrument Calibration pages.

Using Python with CIAO

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.