NS Non-Magnetic Atmosphere Model

NOTE: This model is now in the Xspec release and this page is superceded by the Xspec manual

NOTE: The nsx model has been included as part of the Xspec distribution since version 12.8.2, and should no longer be built as a local model.

20200918: added spectral data for Hydrogen

This model was updated on 4/3/14 to make a small correction to the fitted normalization.

The NSX model interpolates from a grid of neutron star (NS) atmosphere spectra to produce a final spectrum that depends on the parameters listed below. Atmosphere spectra are obtained using opacity tables computed by The Opacity Project and are for non-magnetic atmospheres (note that NSX is fully compatible with the magnetic atmosphere spectral tables of NSMAXG, and both NSX and NSMAXG spectral tables can easily be made compatible with other XSPEC NS fitting models). Atmosphere models are constructed by solving the radiative transfer equation, and the atmosphere is assumed to be in radiative and hydrostatic equilibrium. Atmosphere models depend on the surface effective temperature T_eff and surface gravity g=(1+z_g)GM/R², where 1+z_g=(1-2GM/R)^-1/2 is the gravitational redshift and M and R are the NS mass and radius, respectively. See here for a list of models and model ranges of T_eff, g, and energy.

The model parameters are :

par1			=		logTeff, surface (unredshifted) effective temperature
par2			=		M, neutron star gravitational mass (in units of solar mass)
par3			=		R, neutron star radius (in km)
par4			=		d, distance to neutron star (in kpc)
par5			=		switch indicating model to use (see nsx.dat or model list)
A			=		1, normalization [though not strictly correct, can be varied to change size of emission region, (Rem/R)2]. Note: A is added automatically by XSPEC.

The source code, lmodel.dat entries, input model list (model list read by source code), and model data files (in one tar file) are available. The model data files should either be placed in the $XANADU/spectral/modelData (v12), $XANADU/spectral/xspec/manager (v11) directory, or the XSPEC command xset NSX_DIR directory-path should be used to define the directory containing the model data files.

Please send your comments/questions to Wynn Ho (wynnho@slac.stanford.edu). If you publish results obtained using NSX, please reference Ho, W.C.G. & Heinke, C.O. (2009, Nature, 462, 71).

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