NS Magnetic Atmosphere Model

NOTE: This model is now in the Xspec release and this page is superceded by the Xspec manual

The NSMAX model interpolates from a grid of neutron star (NS) atmosphere spectra to produce a final spectrum that depends on the parameters listed below. The atmosphere spectra are obtained using the latest equation of state and opacity results for a partially ionized, strongly magnetized hydrogen or mid-Z element plasma. The models are constructed by solving the coupled radiative transfer equations for the two photon polarization modes in a magnetized medium, and the atmosphere is in radiative and hydrostatic equilibrium. The atmosphere models mainly depend on the surface effective temperature Teff and magnetic field strength B and inclination ΘB; there is also a dependence on the surface gravity g=(1+zg)GM/R2, where 1+zg=(1-2GM/R)-1/2 is the gravitational redshift and M and R are the NS mass and radius, respectively.

Two sets of models are given: one set with a single surface B and Teff and a set which is constructed with B and Teff varying across the surface according to the magnetic dipole model (for the latter, θm is the angle between the direction to the observer and the magnetic axis). The effective temperatures span the range log Teff=5.5-6.8 for hydrogen and log Teff=5.8-6.9 for mid-Z elements (note: for the latter, change temperature range in nsmax_lmodel.dat). The models with single (B,Teff) cover the energy range 0.05-10 keV, while the models with (B,Teff)-distributions cover the range 0.09-5 keV.

The model parameters are :

par1     =  logTeff, surface (unredshifted) effective temperature
par2     =  1+zg, gravitational redshift
par3     =  switch indicating model to use (see nsmax.dat or model list)
A     =  (Rem/d)2, normalization, where Rem is the size (in km) of the emission region and d is the distance (in kpc) to the object. 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. A list of the models currently available can be found here. The model data files should either be placed in the $XANADU/spectral/modelIonData (v12), $XANADU/spectral/xspec/manager (v11) directory, or the XSPEC command xset NSMAX_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 NSMAX, please reference Ho, W.C.G., Potekhin, A.Y., & Chabrier, G. (2008, ApJS, 178, 102) and also Mori, K. & Ho, W.C.G. (2007, MNRAS, 377, 905) if using the mid-Z models.

Keith Arnaud, X-ray Astrophysics Lab., NASA/Goddard Space Flight Center

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Last modified: Tuesday, 14-Feb-2023 16:42:03 EST