A continuum-only emission spectrum from collisionally-ionized diffuse gas calculated using the ATOMDB code. More information can be found at http://atomdb.org/ which should be consulted by anyone running this model. This default version number can be changed by modifiying the ATOMDB_VERSION string in your Xspec.init file.
See the documentation on the apec model for a list of the xset options which can be used to change the behaviour of the apec code.
The parameters are:
|par1||plasma temperature, keV|
|par2||Metal abundances (He fixed at that defined by the abund command). The elements included are C, N, O, Ne, Mg, Al, Si, S, Ar, Ca, Fe, Ni. Relative abundances are set by the abund command. The trace element abundances are from xset APEC_TRACE_ABUND, the default is 1.0.|
|norm||, where is the angular diameter distance to the source (cm), and are the electron and H densities (cm)|