Version 1.2.8  

S-lang/ISIS Timing Analysis Routines (SITAR) Home Page


SITAR, S-lang/ISIS Timing Analysis Routines, presents a set of functions and subroutines designed to be run within ISIS in order to perform timing analysis of data. The specific examples presented here relate to data obtained with the Chandra X-ray Satellite or with the Rossi X-ray Timing Explorer-All Sky Monitor (RXTE-ASM).

The subroutines are written in S-lang, with reliance on functions intrinsic to ISIS. A few features rely on the use of the GNU Scientific Library module available from the S-Lang Modules Packages. (Specifically, the Gregory-Loredo algorithm, certain options for the Bayesian Blocks routine, and the proper statistical significances of epoch fold values rely on the use of GSL.)

Currently, SITAR provides a set of routines for:

  • Performing a Bayesian Blocks decomposition of a lightcurve, based upon an algorithm and MATLAB codes developed by Jeffrey Scargle.
  • Evenly dividing a lightcurve using the Bayesian algorithm of Gregory & Loredo.
  • Reading RXTE-ASM lightcurves
  • Rebinning rate lightcurves, and rebinning power spectra
  • Period and epoch-folding rate lightcurves
  • Period folding event lightcurves
  • Power and Cross Power Spectral Density functions
New post-Version 1.2.0:
As part of a continuuing revamp of these routines, many of them have been rewritten to change the interface to accept qualifiers (similar to keywords in IDL). Rather than depend upon optional, order-dependent input, one can instead use order independent qualifiers. For example, pre-version 1.2.0:
   isis> y = sitar_pfold_rate(t,rate,2.e4,,,50,3.5e8);
becomes, post-version 1.2.0:
   isis> y = sitar_pfold_rate(t,rate,2.e4;nphs=50,tzero-3.5e8);
   isis> y = sitar_pfold_rate(t,rate,2.e4;tzero-3.5e8,nphs=50);

Some routines still have order-dependent optional inputs (some of the Bayesian Blocks routines - they are slowly being changed over, and are likely to be backwards incompatible with each 0.1 increment in version number). Many of the Power Spectra routines still have order-dependent optiional inputs, since that seemed the more sensible interface.

Please note: Not all of the examples on these web pages have been updated to reflect the new interfaces. Hopefully the translation will be obvious. But eventually all of these routines will be overhauled, and probably updated to a 2.0 status.

Further note: The most up to date versions of these routines, superceding anything on these pages, can be found at the Remeis Observatory ISIS scripts web page.

This page was last updated Oct 21, 2020 by Michael Nowak. To comment on it or the material presented here, send email to
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