Importance of Compton scattering for radiation spectra of isolated neutron stars with weak magnetic fields
Aims:Emergent model spectra of neutron-star atmospheres are widely used to fit the observed soft X-ray spectra of different types of isolated neutron stars. We investigate the effect of Compton scattering on the emergent spectra of hot (T_eff ≥ 106 K) isolated neutron stars with weak magnetic fields.
Methods: In order to compute model atmospheres in hydrostatic and radiative equilibrium we solve the radiation transfer equation with the Kompaneets operator. We calculate a set of models with effective temperatures in the range 1-5×106 K, with two values of surface gravity (log~g = 13.9 and 14.3) and different chemical compositions.
Results: Radiation spectra computed with Compton scattering are softer than those computed without Compton scattering at high energies (E> 5 keV) for light-element (H or He) model atmospheres. The Compton effect is more significant in H model atmospheres and models with low surface gravity. The emergent spectra of the hottest (T_eff >3×106 K) model atmospheres can be described by diluted blackbody spectra with hardness factors ~1.6-1.9. Compton scattering is less important in models with solar abundance of heavy elements.
Astronomy and Astrophysics
- Pub Date:
- May 2007
- radiative transfer;
- methods: numerical;
- stars: neutron;
- stars: atmospheres;
- X-rays: stars;
- 7 pages, 1 table, 6 figures, Accepted for publication in A&