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}=(1-2*GM/R*)^{-1/2} is the
gravitational redshift and *M* and *R* are the NS mass and radius,
respectively. The parameters are:

par1 |
log T |

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 km) |

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 |

The models available by setting par5 are:

Switch |
Element |
log g (cm/s |
log T |
E (keV) |

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, W.C.G. &
Heinke, C.O. (2009, Nature, 462, 71).