apec, vapec:  APEC emission spectrum

An emission spectrum from collisionally-ionized diffuse gas calculated using the APEC code v1.10. More information can be found at

 

http://hea-www.harvard.edu/APEC

 

which should be consulted by anyone running this model. By default this model reads atomic physics data from the files apec_v[version]_coco.fits and apec_v[version]_line.fits in the spectral/xspec/manager file. Different files can be specified by using the command xset set APECROOT. There are three options. APECROOT can be set to a version number (eg 1.1.0, 1.2.0, 1.3.0). In this case the value of APECROOT will be used to replace 1.10 in the name of the standard files and the resulting files will be assumed to be in the $SPECTRAL/xspec/modelIonData 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 and   _line.fits in the manager directory. 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_v1.2.0

 

will use the input files

/foo/bar/apec_v1.2.0_coco.fits

/foo/bar/apec_v1.2.0_line.fits.

 

Thermal broadening of lines can be included by using: xset APECTHERMAL yes.  This runs significantly slower than the option without thermal broadening so you should only use this when necessary.  Velocity broadening of lines can be included by using:  xset APECVELOCITY <velocity>, where <velocity> is in km/s.  This is added in Gaussian quadrature with any thermal broadening in use.

 

The apec model uses abundances set by the abund command. The vapec variant allows the user to set the abundance using additional parameters.

 

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.
par3	Redshift, z
norm	,where DA is the angular size distance to the source (cm), ne and nH are the electron and H densities (cm-3)

For the vapec variant the parameters are as follows. The abundance and redshift parameters are fixed during a fit.

 

par1	plasma temperature, keV
par2-par14	Abundances for He, C, N, O, Ne, Mg,Al, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command)
par15	redshift, z
norm	,where DA is the angular size distance to the source (cm), ne and nH are the electron and H densities (cm-3)