X-ray Pulsar Cyclotron Line Structure from a Two-Component Accretion Cap

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Session 48 -- Degenerate Stars and Pulsars
Display presentation, Thursday, June 15, 1995, 9:20am - 4:00pm

[48.09] X-ray Pulsar Cyclotron Line Structure from a Two-Component Accretion Cap

S.G. Alexander and J. Davila Jr. (Miami University)

Several x--ray pulsars exhibit line structure in their spectra that has been interpreted as originating from cyclotron processes when the radiation scatters from plasma electrons embedded in a strong magnetic field. A few of these objects also show evidence of a second spectral feature that, traditionally, has been thought to be the second cyclotron harmonic. We present detailed calculations of emitted flux spectra for x--ray pulsars that incorporate a two--component model of the accretion cap. The two components are modeled as slabs separated by a shock wave where the post--shock slab is the subsonic high density and temperature plasma that creates the radiation via free--free or bremstrahlung processes and the pre--shock material is represented by a relatively cool low density plasma that is moving near the free--fall velocity. We find that two spectral features are easily produced; one representing the fundamental cyclotron harmonic of the post--shock plasma; and another that is a Doppler shifted line produced by scattering in the pre--shock plasma. Our models include the effects of angle--dependent Doppler shift and aberration. We demonstrate the effect for a range of plasma parameters and compare our results to observations.

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