nsx: neutron star with a non-magnetic atmosphere

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 $g = (1+z_g)GM/R^2$, where $1+z_g = \sqrt{1-2GM/R}$ is the gravitational redshift and $M$ and $R$ are the NS mass and radius, respectively. The parameters are:

par1 $\log T_{eff}$, surface (unredshifted) effective temperature
par2 $M$, neutron star gravitation 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
norm 1, normalization (though not strictly correct, can be varied to change the size of the emission region, $(R_{em}/R)^2$)

The models available by setting par5 are:

Switch Element $\log
g$ (cm/s$^2$) $\log T_{eff}$ E (keV)
1 H 13.6 - 15.0 5.5 - 6.7 0.03 - 15
2 He 13.6 - 14.9 5.5 - 6.7 0.03 - 15
6 C 13.6 - 15.3 5.9 - 6.6 0.01 - 15

If you publish results obtained using nsx, please reference Ho & Heinke (2009).