X-RAY PULSAR 2-LINE SPECTRA FROM A 2-COMPONENT ACCRETION COLUMN

Several X-ray pulsars exhibit line structure in their spectra that has been interpreted as originating from cyclotron processes in the accre ting plasma. A few of these objects also show evidence of a second spe ctral feature that, traditionally, has been thought to be the second c yclotron harmonic. Detailed calculations of the emitted flux spectra a re presented that incorporate a simple two-component model of the accr etion cap. The two components are modeled as slabs separated by a shoc k wave, where the postshock slab is the thermalized high-density and - temperature plasma that creates the radiation via bremsstrahlung proce sses and the preshock material is represented by a relatively cool, lo w-density plasma that is moving near the free-fall velocity. Results s how that two spectral features are easily produced, one representing t he fundamental cyclotron harmonic of the postshock plasma, and another that is a Doppler-shifted line produced by scattering in the preshock plasma.