Chandra Interactive Analysis of Observations
The remarkable science capabilities of the Chandra X-ray Observatory demanded new, flexible, multi-dimensional, software to analyze the data it returned. The result is CIAO - the Chandra Interactive Analysis of Observations - a system that has proven itself useful for the analysis of data from other, non-X-ray missions, because of the mission independence that is the basis of the CIAO design. This document provides an introduction to the CIAO software; more information is available from the CIAO website and via CIAO's command-line help system, ahelp (see "ahelp ahelp").
Introduction to CIAO Tools
CIAO is a data analysis system written for the needs of users of the Chandra X-ray Observatory. Because Chandra is the first mission with 4-dimensional data (2 spatial, time, energy) in which each dimension has many independent elements, CIAO was built to handle N-dimensional data without concern about which particular axes were being analyzed. Also, apart from a few Chandra instrument tools, CIAO is mission independent.
In order to allow users of Chandra data to use pre-existing tools, all CIAO tools read and write several formats, including FITS tables (which includes event files), ASCII formats, and FITS images.
CIAO also needed to be able to filter down and project the 4-D Chandra event data to managable sizes and convenient arrays. This has to be done flexibly, so we have built all CIAO tools to take a `filtering and binning' specification on the command line, making use of a general purpose `regions' syntax. See "ahelp dm" for information on the Data Model that makes all this possible.
Since Chandra data can be sliced and diced in so many ways, and because the Chandra calibration is spatially and energy dependent, we needed to keep track of just how the data had been filtered and binned, which we do in a `data subspace'. The tools keep track of this subspace automatically and allow users to review previous data processing. See "ahelp subspace".
The CIAO design allows close interconnection of tools. For example, the output of any of the source DETECT programs can be fed into dmextract to create a summed spectrum which can then be fit in Sherpa. This feature is used to support the dax (ds9 analysis extensions) package, which users perform many analysis steps directly from DS9.
Modeling and Fitting
The modeling and fitting tool Sherpa is central to the CIAO system. Sherpa performs forward fitting of models to data in N-dimensions. Refer to "ahelp sherpa" and the Sherpa website for details.
Altogether CIAO is a powerful system for the analysis of all types of data.
- See "ahelp ahelp" for an introduction to the CIAO on-line help system
- Use "about <keyword>" for a list of subjects related to your query (ie whatever value you use for <keyword>)
- See "ahelp -c tools" for a list of the tools in CIAO
- See "ahelp dm" for an introduction to the CIAO Data model
- See "ahelp sherpa" for information on modelling and fitting data with Sherpa
Changes in CIAO 4.14
Replacing prism with DS9
The prism tool has been removed, and with it the need to install the GtK+ libraries. The DS9 imaging tool supports most of the functionality of the prism tool.
Running CIAO from DS9
Version 8.3 of DS9, included in this release of CIAO, contains a number of improvements that have been used by the dax (ds9 analysis extensions) package to let users run CIAO tools, and even run Sherpa fitting sessions, directly from the DS9 GUI.
CIAO 4.14 can be run on macOS ARM machines using the Rosetta 2 emulation system and the Intel x86_64 build of CIAO. The CIAO platform-support page provides more details.
Installing CIAO with conda
The conda installation for CIAO has been changed from CIAO 4.13 and now uses the conda-forge channel. It is strongly suggested that users create a new conda environment rather than try to update an existing CIAO 4.13 environment.
Changes in CIAO 4.13
Removal of peg and taskmonitor
The peg and taskmonitor Graphical User Interface tools have been removed in CIAO 4.13. The "Analysis Menu" has been removed from the prism GUI tool.
DS9 and prism-like capabilities
DS9 version 8.2, included in CIAO 4.13, contains a number of improvements to its support for ploting data, including a new "Prism" mode which can be selected either from the File/Prism... menu item or by starting DS9 with the -prism flag:
unix% ds9 -prism
or, to load a specific file (in this case "tbl.fits"),
unix% ds9 -prism tbl.fits