NS Atmosphere models

Neutron star model spectra (angle-averaged surface flux) from Gaensicke, Braje & Romani 2002.

Grids for three compositions can be downloaded : hydrogen (hyd), solar (sol), iron (fe)

Each grid contains 29 spectra, covering log(Teff)=5.1 to log(Teff)=6.5 in steps of log(Teff)=0.05

The models are computed for a canonical neutron star, Mns=1.4Msun, Rns=10km, resulting in a surface gravity log g=14.386 and a redshift z=0.306.

For models with different surface gravities, or for the full angle-dependent intensities, please contact the authors.

Use the grids to fit X-ray data in XSPEC as follows:

XSPEC>model phabs(atable{fe_spectra.mod})
  Model:  phabs[1]( nsspec[2] )
Input parameter value, delta, min, bot, top, and max values for ...
Current:          1     0.001         0         0     1E+05     1E+06
phabs:nH>0.01
Current:       0.05     0.001    0.0108    0.0108     0.272     0.272
nsspec:kT (keV)>0.1
Current:          0    -0.001         0         0         5         5
nsspec:Redshift>0.306
Current:          1      0.01         0         0     1E+24     1E+24
nsspec:norm>1.0

XSPEC>renorm

XSPEC>fit
 ---------------------------------------------------------------------------
 Variances and Principal axes :
               1     2     4
 1.06E-11 | -0.03  0.06  1.00
 3.16E-07 |  0.72  0.70 -0.02
 7.07E-06 |  0.70 -0.71  0.06
  ---------------------------------------------------------------------------
  ---------------------------------------------------------------------------
  Model:  phabs[1]( nsspec[2] )
  Model Fit Model Component  Parameter  Unit     Value
  par   par comp
    1    1    1   phabs      nH       10^22     1.5880E-02 +/- 0.1899E-02
    2    2    2   nsspec     kT (keV)           4.9042E-02 +/- 0.1939E-02
    3    3    2   nsspec     Redshift           0.3060     frozen
    4    4    2   nsspec     norm               2.0179E-04 +/- 0.1537E-03

  Files being used for table models:
  Model comp     File
   2             fe_spectra.mod
  ---------------------------------------------------------------------------
  ---------------------------------------------------------------------------
 Chi-Squared =      136.0014     using    81 PHA bins.
 Reduced chi-squared =      1.743607     for     78 degrees of freedom
 Null hypothesis probability = 5.299E-05

The distance is computed from the normalization as follows:

d[pc] = 1 / sqrt(norm) (70pc for the example above)

Please note that the original instructions on these pages contained an erroneous 1/(1+z) in the equation above. If you used these models, please check that you computed the distance with the correct relation.


Keith Arnaud, Lab. for High Energy Astrophysics, NASA/Goddard Space Flight Center

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