Cyclotron line features from near-critical magnetic fields.

摘要

A detailed analytical study of the resonant cross section for magnetic Compton scattering is performed and use is made of powerful Monte Carlo methods that allow the construction of an innovative numerical scheme for the production of relativistic theoretical cyclotron spectra in scattering atmospheres. The advantages of the Monte Carlo implementation are borne, primarily, in a more accurate evaluation of relativistic angular redistribution of photons and in the allowance for spatial diffusion in arbitrary geometries. Additionally, particular attention is paid to correctly treat magnetic fields close to the electrodynamically critical field {dollar}(Bsb{lcub}crit{rcub}approx44{dollar} TG). All processes and cross sections are calculated using the best known basis properly suitable to the strong field case. The handling of photon spawning includes up to four harmonic energies, allows for scattering into any energetically allowed landau level, and accounts for the effect of a relativistic electron temperature distribution. While an exact formal treatment of the electron-photon interactions including the influence of the relativistic gauge field would be ideal, an attempt is made to strike a balance between accuracy and the finite use of computer resources. This scheme is timely utilized to assess the field strength in X-ray pulsar A0535+26 which shows an absorption line at 110 keV (Grove et al. 1994) but little evidence of lines at lower energies. Our study strongly suggests that A0535+26 possesses the largest magnetic field yet observed. Additionally theoretical line spectra are produced to make specific predictions on the effect of geometry and beamed injection in neutron star Gamma Ray Burst type models.