Resonant Cyclotron Scattering and Comptonization in Neutron Star Magnetospheres

Maxim Lyutikov



Resonant cyclotron scattering of the surface radiation in magnetospheres of neutron stars may considerably modify emergent spectra. Resonant tranfer has a number of unusual characteristics: (i) in the limit of high resonant optical depth, cyclotron resonant layer is half opaque, in a sharp contrast to the case of non-resonant scattering; (ii) transmitted flux is on average Compton up-scattered by 1+ 2 betaT, where betaT is a typical thermal velocity in units of the velocity of light; reflected flux has on average the initial frequency. (iii) for both transmitted and reflected fluxes the dispersion of intensity decreases with increasing optical depth; (iv) emerging spectrum is appreciably non-Plankian while narrow spectral features produced at the surface are erased; (v) optical optical photons are less affected by resonant Comptonization than X-rays due to different polarization of normal modes in resonances. We discuss applications to Anomaous X-ray Pulsars and thermally emitting Isolated Neutron Stars

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