The XSPEC Graphical User Interface is a project funded by Starlink in the UK under the direction of Laurence Jones (U.Birmingham). The programming is done by Tim Ash (Rutherford Appleton Laboratory) in consultation with the author.

The aim of the XSPEC GUI is to make it easier for new users to find their way into the analysis of high energy spectra. We are also adding new capabilities such as using the cursor to include or exclude channels from the fit.

The GUI is implemented as a Tcl/Tk script (currently about 1500 lines long) and as such is very easy to configure and modify. The user's interactions with the GUI are translated into standard XSPEC commands and passed to XSPEC for execution. Output from XSPEC is captured and displayed in a text window.

The plotting is performed using the POW package, which will be familiar from the fv FITS file browser. POW provides a set of Tcl/Tk procedures which are called from the XSPEC GUI script.

Internal XSPEC information is passed to the GUI using the XSPEC tclout command which writes a string to a Tcl variable. For instance, various options of the tclout plot command return the information that XSPEC uses when plotting. This information is then passed to POW for the GUI plotting.

We intend to change the communication between the GUI script and XSPEC to use Internet sockets. This will make the interface cleaner and will also allow us to run XSPEC over the Web.