nei, vnei, vvnei: collisional plasma, non-equilibrium, constant temperature

Non-equilibrium ionization collisional plasma model. This assumes a constant temperature and single ionization parameter. It provides a characterization of the spectrum but is not a physical model. The references for this model can be found under the description of the equil model. Several versions are available. To switch between them use the xset neivers command. The versions available are:

1.0	the version from xspec v11.1
1.1	as 1.0 but with updated ionization fractions using dielectronic recombination rates from Mazzotta et al (1998)
2.0	same ionization fractions as 1.1 but uses AtomDB v2 to calculate the resulting spectrum
3.0	ionization fractions and spectrum calculation uses AtomDB v3

Note that versions 1.x have no emission from Ar. The default is version 3.0. The vnei variant allows the user to set the abundances for the more common elements. For versions 3 and above 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. Full control over all the elemental abundances is available in the vvnei model.

For the nei model the parameters are:

par1	plasma temperature (keV)
par2	Metal abundances (He fixed at cosmic). The elements included are C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni. Abundances are defined by the abund command
par3	Ionization timescale in units of s/cm$^3$.
par4	redshift
norm	$(10^{-14}/(4\pi[D_A(1+z)]^2))\int n_en_H dV$, where $D_A$ is the angular diameter distance to the source (cm), $n_e$ is the electron density (cm$^{-3}$), and $n_H$ is the hydrogen density (cm$^{-3}$).

For the vnei model, the parameters are:

par1	plasma temperature (keV)
par2	H abundance (set to 0 for no free-free continuum, otherwise 1)
par3-par14	Abundances for He, C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command)
par15	Ionization timescale in units of s/cm$^3$.
par16	Redshift, z
norm	$(10^{-14}/(4\pi[D_A(1+z)]^2))\int n_en_H dV$, where $D_A$ is the angular diameter distance to the source (cm), $n_e$ is the electron density (cm$^{-3}$), and $n_H$ is the hydrogen density (cm$^{-3}$).

Finally, for the vvnei model, the parameters are:

par1	plasma temperature (keV)
par2	H abundance (set to 0 for no free-free continuum, otherwise 1)
par3-par31	Abundances for all elements with 2 $\leq$ Z $\leq$ 30 wrt Solar (defined by the abund command)
par32	Ionization timescale in units of s/cm$^3$.
par33	Redshift, z
norm	$(10^{-14}/(4\pi[D_A(1+z)]^2))\int n_en_H dV$, where $D_A$ is the angular diameter distance to the source (cm), $n_e$ is the electron density (cm$^{-3}$), and $n_H$ is the hydrogen density (cm$^{-3}$).