2. Overview

The XRONOS package consists of the following set of independent tasks:

• autocor   - calculates auto correlation for a time series
• crosscor  - calculates cross correlation of two time series
• efold     - creates epoch folded lightcurve, hardness and color-color plots
• efsearch  - finds best chi-squared period by folding over range of periods
• listdata  - list data file on the screen
• lcstats   - calculates statistical variables a time series
• lcurve    - creates lightcurves, hardness and color-color plots
• powspec   - creates power spectrum density
• timeskew  - calculates time skewness function for a time series
• xronwin   - creates a window file suitable for xronos tasks
• ascii2flc - creates a xronos input FITS file from an ASCII file
• flc2ascii - dumps xronos input or output into ASCII file readable by QDP
• lcmath    - subtracts or adds two binned lightcurves
• rbf2fits  - converts the "EXOSAT rate buffer" format into FITS
• earth2sun - change times to solar system barycenter

The simplest way to use a XRONOS task is to execute the task from the command line and answer the prompts. Defaults are indicated in square brackets, and may be selected by simply pressing Enter. Those prompts correspond to parameters which may be specified when the task is executed by using the syntax parameter=value. For a full list of parameters for a particular task use the plist utility with the task name as its argument.

All output to the screen can be written to log files by specifying a log chat level with the lchat parameter. The log file is named xronos.log by default, however it may be specified through the logname parameter. For example, powspec lchat=10 logname=powspec.log would record a log of the execution of powspec. While a task is prompting the user for an input, the task can be terminated by entering an interruption (cntl c) during execution.

2.1 Reading Data

XRONOS tasks will read in time series from many consecutive input files (this is to avoid wasting disk space by chaining many input files in a single file) through the use of a filelist, a text file containing a line for each input file, separating time series with a ///. The filelist is input using the syntax @filelist. Additional flexibility is provided by Input File Options, which are used, e.g. to perform algebraic operations on individual input files, shift times, apply barycentric time corrections etc.

The primary input file format used by XRONOS tasks is FITS, although platform-dependent Rate Buffers (with extension .rbf) may be converted with rbf2fits and QDP files, which are ASCII files written according to the QDP/PLT standard may be converted with ascii2flc. XRONOS input files can either contain binned data or unbinned data (i.e. input files containing the arrival times of individual photons, also known as an event list).

2.2 Terminology

Within XRONOS tasks, BINS and NEWBINS control the binning used in the analysis, INTERVALS the subdivision of the time series and FRAME the grouping of the output results:

• BINS : these are the time bins of the time series being analysed. More than one input file can have different bin durations, e.g. two consecutive time series, one with 0.5 s bins and the other with 2 s bins. The original bin time is the value stored in the input file in the keyword TIMEDEL. If the data are stored in each row as an array with 1CTYPn = 'TIME', the original bin is set to the value stored in the keyword 1CDLTn (where n is the column number).

• NEWBINS : these correspond to the time resolution at which the analysis is carried out. Note that: (i) newbins cannot be shorter than the longest bin duration of the time series being analysed; (ii) in many XRONOS applications (e.g. powspec, autocor, crosscor) the newbin duration is forced to be an integer multiple of the longest bin duration.

• INTERVALS : an interval is defined by the number of newbins over which the analysis is carried out. Note that in applications using FFT algorithms (i.e. powspec, autocor and crosscor set in fast mode) the number of newbins in an interval is a power of 2.

• FRAMES : a frame consists of the average of the results of the analysis of one or more contiguous intervals. Each plot produced by XRONOS corresponds to a frame. Note that in lcurve, efsearch and lcstats a frame consists always of one interval.

2.3 Windows

There are 4 different types of windows which can be specified within XRONOS: time, phase, intensity and exposure windows. In applications requiring more than one input series (e.g. a cross-correlation analysis) intensity and exposure windows are specified separately for each series. Intensity and exposure windows can be specified separately for bins, newbins and intervals. The xronwin task will create, read or change XRONOS window files (default extension .wi). Many XRONOS application use some default exposure windows, which are designed to avoid analysing data sets which are too inhomogeneous with respect to their statistical properties.

2.4 Plotting

Most XRONOS tasks plot their results using QDP/PLT and the default PGPLOT device, /XW, in a new window. The task will give a PLT> prompt while in this mode. There are many commands that may be used to customize the current plot, which are fully documented in the QDP/PLT manual ( http://heasarc.gsfc.nasa.gov/lheasoft/ftools/others/qdp/qdp.html ). The "QDP/PLT" section of this manual provides some commonly used commands. Use exit to leave the PLT prompt. The parameter setting plot=no may be used to bypass plotting.

2.5 XRONOS HEAsoft

All tasks uses the Xanadu Paramater Interface based on the IRAF parameter file style. This is the standard interface used by all tools distributed within HEAsoft. There are a number of useful programs, distributed with HEAsoft, that manipulate the XRONOS parameter files:

• plist - List parameters from one or more IRAF-style parameter files
• pget - Get the value of one or more parameters in a parameter file
• pset - Set one or more parameters in an IRAF-style parameter file
• punlearn - Get a copy of the system parameter file

The plist program is useful for seeing a task's parameters and their current values. Its output takes the following form (hidden parameters are in parentheses):

    > plist task
    Parameters for /home/user/pfiles/task.par
         requiredparm = defaultvalue     Prompt question
          (hiddenparm = defaultvalue)    Parameter info

The pget program returns the default values of specific parameters. For example:

    > pget lcurve cfile
    me_a52385.lc.Z

The pset program assigns the default values of specific parameters. This is most useful to change the default for hidden parameters. For example, efold assumes the period is in units of seconds (perfo=2). If days is a more convenient unit, the default may be permanently changed as follows:

    > pset efold perfo=1

To restore the parameters to their original values, removing any hidden parameter modifications that have been made with pset, run:

    > punlearn efold

2.6 Getting Help

The on-line help can be invoked using the task fhelp distributed with HEAsoft. To get a list of all tasks in the XRONOS package, use fhelp xronos. For help on individual tasks, use fhelp followed by the name of the task.