Magnetized neutron star atmospheres: Beyond the cold plasma approximation

All magnetized neutron star model atmospheres hitherto computed use opacities calculated in the cold plasma approximation. Here we present models of hydrogen neutron star atmospheres with the thermal cyclotron opacities taken into account. The parameters of the atmospheres are typical for the so-called central compact objects in supernova remnants, such as 1E 1207.4–5209 in PKS 1209–51/52. We show that the Doppler cores of the first three cyclotron harmonics can be significant for the interpretation of observable absorption features, in addition to the quantum oscillations in magnetic free-free opacity. The absorptions due to the quantum oscillations determine the total equivalent widths, but the relative contributions of the Doppler cores grow with increasing quantization parameter b_eff ≡ E_c,e/kT_eff and harmonic number. The total equivalent widths of the features can reach ∼ 100–250 eV; they increase with growing b_eff and are smaller for higher harmonics.