apec

apec, vapec, vvapec: APEC emission spectrum

An emission spectrum from collisionally-ionized diffuse gas calculated using the ATOMDB code v2.0.2. 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 and line data from the files apec_v[version]_coco.fits and apec_v[version]_line.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 and _line.fits files. 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 sigma 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 and vvapec variants allow the user to set the abundance using additional parameters. For apec and vapec 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 Fe

sets trace element abundances to that of iron while

XSPEC12> xset APEC_TRACE_ABUND 1.0

sets 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.

For the apec model 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.
par3	Redshift, z
norm	,where D_A is the angular diameter distance to the source (cm), n_e and n_H are the electron and H densities (cm^-3)

For the vapec variant the parameters are as follows.

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). The trace element abundances are from xset APEC_TRACE_ABUND, the default is 1.0.
par15	redshift, z
norm	,where D_A is the angular diameter distance to the source (cm), n_e and n_H are the electron and H densities (cm^-3)

For the vvapec variant the parameters are as follows.

Par1	plasma temperature, keV
par2-par31	Abundances for H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn wrt Solar (defined by the abund command)
Par32	redshift, z
norm	,where D_A is the angular diameter distance to the source (cm), n_e and n_H are the electron and H densities (cm^-3)