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.
By default this model reads atomic physics continuum data from the file apec_v[version]_coco.fits in the $HEADAS/../spectral/modelData directory. Different files can be specified by using the command xset APECROOT. There are three options. APECROOT can be set to a version number (eg 1.10, 1.2.0, 1.3.1, 2.0.1). In this case the value of APECROOT will be used to replace 2.0.2 in the name of the standard files and the resulting files will be assumed to be in the modelData directory. Alternatively, a filename root (eg apec_v1.2.0) can be given. This root will be used as a prefix for the _coco.fits . Finally, if neither of these work then the model will assume that the APECROOT value gives the complete directory path, e.g.
XSPEC12> xset APECROOT /foo/bar/apec_v1.2.0will use the input file /foo/bar/apec_v1.2.0_coco.fits.
The nlapec model uses abundances set by the abund command. The abundances of the trace elements (ie Li, Be, B, F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu, Zn) can be set using xset APEC_TRACE_ABUND. These trace element abundances can be set either to the abundance of one of the main elements or to a numerical value (relative to Solar). For instance,
XSPEC12> xset APEC_TRACE_ABUND Fesets trace element abundances to that of iron while
XSPEC12> xset APEC_TRACE_ABUND 1.0sets them to Solar. The default value for APEC_TRACE_ABUND is 1.0. Note that this means that the apec and vapec models will show emission lines even if the abundance parameters are set to zero.
The parameters are:
|par1||plasma temperature, keV|
|par2||Metal abundances (He fixed at cosmic). 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)|