Chandra X-Ray Observatory
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Last modified: 13 December 2018


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 4.10
& CALDB 4.8.2

Read the CIAO 4.10 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?

Note: CIAO 4.10 defaults to using Python 3.5, as support for Python 2.7 in the scientific-software ecosystem is coming to an end. Please read about the CXC's plan to only support Python 3.5 in the next release of CIAO.

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.

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

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.

Scripting in CIAO

CSC v2: Chandra Source Catalog 2
CSC v1: Chandra Source Catalog 1.1
TGCat: Chandra Gratings Catalog

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.

Last modified: 13 December 2018
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The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA.   Email: Smithsonian Institution, Copyright © 1998-2017. All rights reserved.