AAS 198th Meeting, June 2001
Session 27. Neutron Stars, Pulsars Gamma ray Bursts
Oral, Monday, June 4, 2001, 2:00-3:30pm, C107

[27.02] Atmospheres and Spectra of Strongly Magnetized Neutron Stars

W.C.G. Ho, D. Lai (Cornell University)

We construct atmosphere models for strongly magnetized neutron stars with surface fields B~1012-1014~G and effective temperatures T\rm eff~106-107~K. The atmosphere consists of pure hydrogen or helium and is assumed to be fully ionized. The radiative opacities include free-free absorption and scattering by both electrons and ions computed for the two photon polarization modes in the magnetized electron-ion plasma. In the case where the angle \ThetaB between the magnetic field and the surface normal is zero, we solve the full, angle-dependent, coupled radiative transfer equations for both polarization modes. We also construct atmosphere models for general \ThetaB based on the diffusion approximation of the transport equations and compare the results with models based on full radiative transport. Because of the significant opacity suppression by the magnetic field, the radiation is mainly carried by the extraordinary mode photons, which emerge from deep in the atmosphere. In such high density regions, plasma effects can significantly modify the photon opacities by changing the properties of the polarization modes. In general, the emergent thermal radiation exhibits significant deviation from blackbody, with harder spectra at high energies. The spectra also show a broad feature (\Delta E/EBi~1) around the ion cyclotron resonance EBi=0.63\,B14~keV. Detection of this feature would provide a direct measurement of the surface magnetic fields on radio pulsars and magnetars.