|AHELP for CIAO 4.9 Sherpa v1||
Sedov model with electron and ion temperatures. XSPEC model.
Sedov model with separate ion and electron temperatures. This model is slow. kt_a provides a measure of the average energy per particle (ions + electrons) and is constant throughout the post-shock flow in plane shock models (Borkowski et al., 2001, ApJ, 548, 820). kt_b should always be less than kt_a. If kt_b exceeds kt_a then their interpretations are switched (i.e. the larger of kt_a and kt_b is always the mean temperature). Additional references for this model can be found in the help file for the xsequil model.
See also the xsvsedov and xsvvsedov 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.
|1||kT_a||mean temperature in keV|
|2||kT_b||electron temperature immediately behind the shock front (keV)|
|3||Abundanc||Metal abundances (He fixed at cosmic). The elements included are C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni in ratios set by the set_xsabund command.|
|4||Tau||ionization age (s/cm^3) of the remnant (= electron density immediately behind the shock front multiplied by the age of the remnant)|
|6||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)|
This information is taken from the XSPEC User's Guide. Version 12.9.0o of the XSPEC models is supplied with CIAO 4.9.
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', '/path/to/heasoft-6.19/spectral/modelData/APEC_nei_v11')
where "/path/to" should be replaced by the location where the tar file was unpacked.
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() '12.9.0o'
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