CIAO (Chandra Interactive Analysis of Observations) is the software package that was first released in 1999 following the launch of the Chandra X-ray Observatory and is used by astronomers across the world to analyze Chandra data as well as data from other telescopes. I have been part of the core group involved in the design, specification, testing and documentation of the CIAO software since I started to work at the CXC. I am also involved in supporting the many users of the CIAO software.

CIAO can be obtained from the download page

If you are writing a paper and use CIAO for the analysis, we would be grateful if you could cite CIAO with the following reference:
CIAO: Chandra's data analysis system
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

CIAO: Chandra's data analysis system [PDF]
Fruscione, Antonella; McDowell, Jonathan C.; Allen, Glenn E.; Brickhouse, Nancy S.; Burke, Douglas J.; Davis, John E.; Durham, Nick; Elvis, Martin; Galle, Elizabeth C.; Harris, Daniel E.; Huenemoerder, David P.; Houck, John C.; Ishibashi, Bish; Karovska, Margarita; Nicastro, Fabrizio; Noble, Michael S.; Nowak, Michael A.; Primini, Frank A.; Siemiginowska, Aneta; Smith, Randall K.; Wise, Michael

Observatory Operations: Strategies, Processes, and Systems. Edited by Silva, David R.; Doxsey, Rodger E.. Proceedings of the SPIE, Volume 6270, pp. 62701V (2006).
Published in Jul 2006

The CIAO (Chandra Interactive Analysis of Observations) software package was first released in 1999 following the launch of the Chandra X-ray Observatory and is used by astronomers across the world to analyze Chandra data as well as data from other telescopes. From the earliest design discussions, CIAO was planned as a general-purpose scientific data analysis system optimized for X-ray astronomy, and consists mainly of command line tools (allowing easy pipelining and scripting) with a parameter-based interface layered on a flexible data manipulation I/O library. The same code is used for the standard Chandra archive pipeline, allowing users to recalibrate their data in a consistent way. We will discuss the lessons learned from the first six years of the software's evolution. Our initial approach to documentation evolved to concentrate on recipe-based "threads" which have proved very successful. A multi-dimensional abstract approach to data analysis has allowed new capabilities to be added while retaining existing interfaces. A key requirement for our community was interoperability with other data analysis systems, leading us to adopt standard file formats and an architecture which was as robust as possible to the input of foreign data files, as well as re-using a number of external libraries. We support users who are comfortable with coding themselves via a flexible user scripting paradigm, while the availability of tightly constrained pipeline programs are of benefit to less computationally-advanced users. As with other analysis systems, we have found that infrastructure maintenance and re-engineering is a necessary and significant ongoing effort and needs to be planned in to any long-lived astronomy software.


Chandra Newsletter articles about CIAO

 2013 CIAO 4.5: Improved tools and Sherpa, ability to merge observations, and now featured on YouTube
 2012 CIAO 4.4: Improved tools, a new graphical interface for plotting and advanced Sherpa functionality
 2011 CIAO 4.3: Pushing the Chandra Spatial Resolution to its Limit [PDF]
 2010 CIAO 4.2: with the power of Phython!
 2009     CIAO 4.1: with a whole new Sherpa!
 2008 CIAO 4.0: Overview
CIAO 4.0 Infrastructure: Moving in a modular direction
 2005 Data Analysis: Do I Need to Reprocess My Data?
 2004 CIAO 3.0: Empowering the Users
 2003 CIAO: "Why? Topics" and "Analysis Guides": A Deeper and Wider Perspective
CIAO: Focus on threads
CIAO 2: New software and Documentation
CIAO: at your service!