Skip to the navigation links
Last modified: 4 June 2024


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 4.16 & CALDB 4.11.2

Read the CIAO 4.16 release notes for detailed information on this release, including How CALDB 4.11.2 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 your choice of Python 3.11, 3.10, or 3.9 when using the conda installation method, and Python 3.11 when using ciao-install 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.

CIAO 4.16 includes several important bug fixes as well as supports newer compliers, native support for Apple's M1/M2/M3 chip [New], and updated Off the Shelf software. This includes Sherpa improvements, containing the XSPEC 12.13.1e models, and SAOImage DS9 v8.5 with its own SAMP hub.

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

A Chandra Pocket Guide

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

Welcome to CIAO
Introduction to the Tools & Applications

Introductory Science Threads - Beginners should start here

Download CIAO 4.16 using the ciao-install script
Download CIAO 4.16 with conda

Quick Start Guide

All CIAO Threads

Analysis Guides
YouTube videos

Chandra/CIAO Workshops

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 | PDF | 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.