XSPEC is a command-driven, interactive, X-ray spectral-fitting program. It is designed to be completely detector-independent so that it can be used for any spectrometer. To our knowledge, XSPEC has been used to analyze data from HEAO-1 A2, Einstein Observatory, EXOSAT, Ginga, ROSAT, BBXRT, ASCA, CGRO, and IUE. It also has been used for simulations for XTE and AXAF. This manual describes XSPEC v9.00, which runs under VAX/VMS, Alpha/OpenVMS, SunOS, Solaris 2.x, HP/Unix, DEC/Ultrix, Alpha/OSF, SGI, IBM/AIX, and NeXT (with the Oasys fortran compiler) systems.
The new user is advised to read Chapter 2, which introduces spectral fitting and the XSPEC approach, Chapter 3, which gives an overview of the program commands, and Chapter 4, which contains walk-throughs of XSPEC sessions. She then should experiment with XSPEC and, if necessary, look up individual commands in Chapter 5, or descriptions of the spectral models in use, in Chapter 6. Some of the FTOOLS that can operate on XSPEC files are listed in Chapter 7. XSPEC uses the PLT plotting package, which is described briefly in Appendix A and in more detail in the ``QDP/PLT User's Guide" (Tennant, 1989). Users possessing X-ray spectra with small numbers of counts per bin are referred to Appendix B, which describes the C-statistic option. Users interested in adding their own models can read how to do so in Appendix C. The XSPEC/PLT parser is described in Appendix D and, finally, some programs that operate on the old-XSPEC format files are described in Appendix E.