NS Magnetic Atmosphere Model

NOTE: This model is now in the Xspec release and this page is superceded by the Xspec manual

This model was updated on 9/20/16 with changes to five input tables. The tables for models HB1200ThB00 and HB1300ThB00 have been recomputed with results from recent work and have twice the number of energy grid points and extend to a higher temperature (logTeff=6.8 vs 6.7 previously). The tables for models HB1060ThB00, HB1085ThB00, and HB1100ThB00 are now computed assuming a partial ionized hydrogen atmosphere (previously was completely ionized) and they also allow for variation of surface gravity in the Xspec fitting (as allowed previously for a few other tables).

The NSMAXG 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 the latest equation of state and opacity results for a partially ionized, strongly magnetized hydrogen or mid-Z element plasma. 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. 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 [some models allow for varying g, in the range log g (cm s^-2) = 13.6-15.4] and a set which is constructed with B and T_eff varying across the surface according to the magnetic dipole model (θ_m is the angle between the direction to the observer and the magnetic axis). Effective temperatures span the range log T_eff (K) ≈ 5.5-6.8. Models with single (B,T_eff) cover the energy range 0.05-10 keV, while models with (B,T_eff)-distributions cover the range 0.09-5 keV. See here for a list of models. (Note that the spectral tables can easily be made compatible with other XSPEC NS fitting models.)

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 nsmaxg.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/modelIonData (v12), $XANADU/spectral/xspec/manager (v11) directory, or the XSPEC command xset NSMAXG_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 NSMAXG, 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 mid-Z models. See Ho, W.C.G. (2014, Proc. of IAUS 302, 435) for discussion of NSMAXG and NSMAX.

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