gtburstfit Help File

Analyzes burst light curves by applying a Bayesian algorithm to determine the optimum set of blocks to follow the burst profile shape, then optionally fitting a model to the data using the Bayesian Block definitions to determine the number of model components and initial values for the model parameters.

Usage: gtburstfit evfile fitguess amp time0 tau1 tau2 bckgnd

Blocks may also be used by gtburstfit to construct a pulse model, which gtburstfit can fit to the data. The model used to fit the data is a constant background added to a sum of terms of the form:

A * exp(tau1 / (t - time0) + (t - time0) / tau2)

where

A is the amplitude of the pulse, time0 is the time of the pulse,
tau1 is the "Rise Coefficient", and tau2 is the "Decay Coefficient" of
the pulse.

gtburstfit automatically determines the number of these terms by looking for peaks and valleys in the Bayesian block definitions, and bt using these to determine the number of peaks detected, and their approximate positions, heights, and widths.

As input, gtburstfit uses a time binned data file. The original event data file can be obtained from SLAC's Data Portal, and can be binned using gtbin with the light curve (LC) option.

gtburstfit's output includes the: values of the amplitude; time of the pulse; "Rise Coefficient" and "Decay Coefficient" for each pulse; background coefficient; and Chi Square of the fit. By default the tool displays: a plot showing the data; the Bayesian Blocks (which were created for the data); and the results of the fit. The user may zoom in the resulting plot using the left mouse button. The right mouse button can be used to add new peaks to the model, and these can be included on subsequent runs of the tool when gui=yes and fitguess=calc only).

Examples: gtburstfit

Parameters are passed following the FTOOLs model (i.e., they can be passed interactively by: answering a prompt; as a list in a command line; or by editing the parameter file).

To be prompted for gtburstfit parameter values, simply type (at the command line): gtburstfit

Note: Not all parameters are prompted; some parameters are "hidden". To change a "hidden" parameter, specify its value in the command line. For example, if you want to include a title in your plot, you can set the parameter title at the command line by entering:

gtburstfit title=MyPLOT

where

"MyPLOT" will be the title of your plot.

An example of how to run gtburstfit using the AUTO option is given below:

An example of how to run the tool using the MAN option is given below:

KNOWN BUGS:

When using fitguess=AUTO and running gtburstfit multiple times in the GUI mode (gui=yes), the values of the rise and decay coefficients, tau1 and tau2, are not correctly computed from the "Pulse start", "Peak" and "Decay" markers on the graph. This has the effect that if one re-runs the tool without making any changes, the initial guesses for tau1 and tau2 for the next run will not be the same as the final values from the previous run.