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NOTE: This model is now in the Xspec release and this page is superceded by the Xspec manual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 T_eff and magnetic field strength B and inclination Θ_B; there is also a dependence on the 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.

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

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