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1. Introduction

XRONOS is a general purpose timing analysis package. Although it was designed mostly for X-ray astronomy, XRONOS is basically detector and wavelength-independent. It has been used to analyse data from the Einstein Observatory, EXOSAT, Ginga, ASCA and RXTE, as well as optical photometry. It includes programs for: lightcurve(s), hardness ratio and colour-colour plotting, epoch folding, power spectrum, autocorrelation, cross-correlation, time skewness and statistical analysis.

XRONOS consists of a collection of tools, each dedicated to one task, that use a parameter file interface. Parameters may be specified as arguments when the tool is executed or prompted from within the tool.

1.1 Timing analysis

This manual describes how to run the XRONOS programs; obviously, it is not a treatise on the technique of timing analysis. Some references describing the relevant techniques are given. If the user is completely new to the field, he should first talk to an expert.

1.2 History

XRONOS is a descendant of a series of timing analysis programs written at the EXOSAT Observatory to analyse interactively the EXOSAT data on Hewlett Packard Series 1000 minicomputers. The development of XRONOS started in 1987 during the post operational phase of the EXOSAT project. XRONOS was designed to provide a timing analysis package as independent of the detectors as possible, so that it could be used for future missions with few if any changes. Some of the original design characteristics of XRONOS were deeply influenced by the experience with the analysis of large sets of high time resolution EXOSAT data. In order to limit the number of page folds, while retaining the array sizes needed, e.g., for the fast Fourier transform (FFT) of large data sets, it was decided that XRONOS should consist of a collection of programs, each dedicated to one task.

A preliminary version of XRONOS was developed under UNIX on a Hewlett Packard 9000 computer. This was ported to VAX/VMS in 1988 to make XRONOS produce light curves within the EXOSAT database system. The number of XRONOS applications grew rapidly in 1989. Version 3.00 (July 1992) was the first complete portable version of XRONOS. Version 4.02 extended XRONOS to include FITS input and output file support and Version 5.0 the user interface changed to use the Xanadu Parameters Interface (XPI). The package is now fully integrated within the HEAsoft distributed by the HEASARC.

1.3 Installation

The XRONOS package can be obtained for several platforms including Dec-OSF, SunOS, and Linux. Compressed tar files can be obtained at or write to

1.4 Reporting problems

Any problems in obtaining or installing XRONOS should be reported to Any questions or problems with XRONOS or requests to add additional instruments should be directed to or

1.5 Acknowledgements

The first version of XRONOS was written by L. Stella. L. Angelini contributed with the I/O routines, testing, and to produce a portable version of XRONOS. P. Giommi, A. Parmar, A. Pollock, G. Tagliaferri, M. van der Klis and N. White provided several fortran routines and a number of suggestions.

next up previous contents
Next: 2. Overview Up: XRONOS User's Guide Previous: Contents   Contents
Alex Padgett 2009-08-21