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Last modified: December 2015

AHELP for CIAO 4.9 Sherpa v1


Context: models


Non-equilibrium ionization collisional plasma model with variable abundances for all elements with Z <= 30. XSPEC model.


Non-equilibrium ionization collisional plasma model. This is a generalization of the xsnei model where the temperature is allowed to have been different in the past, i.e. the ionization timescale averaged temperature is not necessarily equal to the current temperature. For example, in a standard Sedov model with equal electron and ion temperatures, the ionization timescale averaged temperature is always higher than the current temperature for each fluid element. The references for this model can be found in the help file for the xsequil model.

See also the xsgnei and xsvgnei models.

Several versions are available. To switch between them use the set_xsxset command: set_xsxset('NEIVERS', '1.0') gives the version from XSPEC v11.1; set_xsxset('NEIVERS', '1.1') uses updated calculations of ionization fractions using dielectronic recombination rates from Mazzotta et al (1998); set_xsxset('NEIVERS', '2.0') uses the same ionization fractions as 1.1 but uses APED to calculate the resulting spectrum; and set_xsxset('NEIVERS', '3.0') uses the beta release from AtomDB 3.0. Note that versions 1.x have no emission from Ar. The default is version 3.0.

This is an additive model component.

xsvvgnei Parameters

Number Name Description
1 kT plasma temperature (keV)
2 H Hydrogen density in cm^-3
3-31 (element) Abundances for all elements with Z <= 30 with respect to Solar (defined by the set_xsabund command)
32 Tau ionization timescale in units of s/cm^3
33 kT_ave ionization timescale averaged plasma temperature in keV
34 redshift redshift, z
35 norm 10^-14 / (4 pi (D_A*(1+z))^2) Int n_e n_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)

XSPEC version

This information is taken from the XSPEC User's Guide. Version 12.9.0o of the XSPEC models is supplied with CIAO 4.9.

Using NEIVERS 2.0

The data files needed when version 2.0 of NEIVERS are not provided with Sherpa (or X-Spec) and must be downloaded separately: XSPEC data for APEC NEI Models (19Mb). Once unpacked, it will create the directory heasoft-6.19/spectral/modelData/ and the two files can either be moved to $ASCDS_INSTALL/ots/spectral/modelData/ or the NEIAPECROOT variable set to

sherpa> set_xsxset('NEIAPECROOT',

where "/path/to" should be replaced by the location where the tar file was unpacked.

Checking it worked

To check that this works, try:

sherpa> set_xschatter(25)
sherpa> set_xsxset('NEIVERS', '2.0')
sherpa> create_model_component('xsnei', 'mdl')
sherpa> mdl([0.1, 0.2, 0.3, 0.4, 0.5])

which will evaluate the xsnei model over the bins 0.1-0.2, 0.2-0.3, 0.3-0.4, and 0.4-0.5 keV, and - as the X-Spec chatter level has been increased to 25 - will also print messages to the screen showing what files were used or if there was an error loading them.


For a list of known bugs and issues with the XSPEC models, please visit the XSPEC bugs page.

To check the X-Spec version used by Sherpa, use the get_xsversion routine from the xspec module:

sherpa> from sherpa.astro.xspec import get_xsversion
sherpa> get_xsversion()

See Also

absorptionedge, absorptiongaussian, absorptionlorentz, absorptionvoigt, accretiondisk, atten, bbody, bbodyfreq, beta1d, beta2d, blackbody, box1d, box2d, bpl1d, bremsstrahlung, brokenpowerlaw, ccm, const1d, const2d, cos, delta1d, delta2d, dered, devaucouleurs2d, disk2d, edge, emissiongaussian, emissionlorentz, emissionvoigt, erf, erfc, exp, exp10, fm, gauss1d, gauss2d, hubblereynolds, jdpileup, linebroad, list_model_components, list_models, lmc, load_xscflux, load_xsgsmooth, load_xsireflect, load_xskdblur, load_xskdblur2, load_xskerrconv, load_xslsmooth, load_xspartcov, load_xsrdblur, load_xsreflect, load_xssimpl, load_xszashift, load_xszmshift, log, log10, logabsorption, logemission, logparabola, lorentz1d, lorentz2d, models, normbeta1d, normgauss1d, normgauss2d, opticalgaussian, poisson, polynom1d, polynom2d, polynomial, powerlaw, powlaw1d, recombination, scale1d, scale2d, schechter, seaton, sersic2d, shell2d, sigmagauss2d, sin, sm, smc, sqrt, stephi1d, steplo1d, tablemodel, tan, xgal, xs, xsabsori, xsacisabs, xsagauss, xsapec, xsbapec, xsbbody, xsbbodyrad, xsbexrav, xsbexriv, xsbkn2pow, xsbknpower, xsbmc, xsbremss, xsbvapec, xsbvvapec, xsc6mekl, xsc6pmekl, xsc6pvmkl, xsc6vmekl, xscabs, xscemekl, xscevmkl, xscflow, xscompbb, xscompls, xscompmag, xscompps, xscompst, xscomptb, xscompth, xscomptt, xsconstant, xsconvolve, xscplinear, xscutoffpl, xscyclabs, xsdisk, xsdiskbb, xsdiskir, xsdiskline, xsdiskm, xsdisko, xsdiskpbb, xsdiskpn, xsdust, xsedge, xseplogpar, xseqpair, xseqtherm, xsequil, xsexpabs, xsexpdec, xsexpfac, xsezdiskbb, xsgabs, xsgadem, xsgaussian, xsgnei, xsgrad, xsgrbm, xsheilin, xshighecut, xshrefl, xskerrbb, xskerrd, xskerrdisk, xslaor, xslaor2, xslogpar, xslorentz, xslyman, xsmeka, xsmekal, xsmkcflow, xsnei, xsnotch, xsnpshock, xsnsa, xsnsagrav, xsnsatmos, xsnsmax, xsnsmaxg, xsnsx, xsnteea, xsnthcomp, xsoptxagn, xsoptxagnf, xspcfabs, xspegpwrlw, xspexmon, xspexrav, xspexriv, xsphabs, xsplabs, xsplcabs, xsposm, xspowerlaw, xspshock, xspwab, xsraymond, xsredden, xsredge, xsrefsch, xsrnei, xssedov, xssirf, xssmedge, xsspexpcut, xsspline, xssrcut, xssresc, xssss_ice, xsstep, xsswind1, xstbabs, xstbgrain, xstbvarabs, xsuvred, xsvapec, xsvarabs, xsvbremss, xsvequil, xsvgadem, xsvgnei, xsvmcflow, xsvmeka, xsvmekal, xsvnei, xsvnpshock, xsvphabs, xsvpshock, xsvraymond, xsvrnei, xsvsedov, xsvvapec, xsvvnei, xsvvnpshock, xsvvpshock, xsvvrnei, xsvvsedov, xswabs, xswndabs, xsxion, xszagauss, xszbabs, xszbbody, xszbremss, xszdust, xszedge, xszgauss, xszhighect, xszigm, xszpcfabs, xszphabs, xszpowerlw, xszredden, xszsmdust, xsztbabs, xszvarabs, xszvfeabs, xszvphabs, xszwabs, xszwndabs, xszxipcf

Last modified: December 2015
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