AAS 207th Meeting, 8-12 January 2006
Session 198 Neutron Stars and Pulsars
Oral, Thursday, 10:00-11:30am, January 12, 2006, Balcony B

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[198.01] Bulk and Thermal Comptonization in Accretion Powered X-Ray Pulsars

P. A. Becker (George Mason University), M. T. Wolff, K. D. Wolfram (Naval Research Laboratory)

Accretion-powered X-ray pulsars are among the most luminous X-ray sources in the Galaxy. However, despite decades of theoretical and observational work since their discovery, no satisfactory model for the formation of the observed X-ray spectra has emerged. In this paper, we present the first self-consistent calculation of the spectrum emerging from a pulsar accretion column that includes an explicit treatment of the bulk and thermal Comptonization occurring in the accretion shock. Using a rigorous eigenfunction expansion method, we obtain a closed-form expression for the Green's function describing the upscattering of monochromatic radiation injected into the column. The Green's function is convolved with bremsstrahlung, cyclotron, and blackbody source terms to calculate the emergent photon spectrum. We demonstrate that the energization of the photons in the shock naturally produces an X-ray spectrum with a relatively flat continuum shape leading up to a high-energy exponential cutoff. In particular, we demonstrate good agreement with the spectrum of the bright pulsar Her X-1.

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