8th HEAD Meeting, 8-11 September, 2004
Session 25 X-ray Binaries and White Dwarfs
Poster, Friday, September 10, 2004, 9:00am-10:00pm

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[25.18] Spectral Formation in X-Ray Pulsar Accretion Columns

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

We present the first self-consistent model for the dynamics and the radiative transfer occurring in bright X-ray pulsar accretion columns, with a special focus on the role of the shock in energizing the emerging X-rays. Because the pressure inside the accretion column of a luminous X-ray pulsar is dominated by the photons, the equations describing the coupled radiative-dynamical structure must be solved simultaneously making spectral formation in these sources is a complex nonlinear problem. We obtain the analytical solution for the Green's function describing the upscattering of monochromatic radiation injected into the column from the thermal mound located near the base of the flow. The Green's function is convolved with a Planck distribution to model the X-ray spectrum resulting from the reprocessing of blackbody photons produced in the thermal mound. These photons diffuse through the infalling gas and eventually escape out the walls of the column, forming the observed X-ray spectrum. We show that the resulting column-integrated, phase-averaged spectrum has a power-law shape at high energy and a blackbody shape at low energy, in agreement with the observational data for many X-ray pulsars.

This research was supported by the Office of Naval Research.

The author(s) of this abstract have provided an email address for comments about the abstract: michael.wolff@nrl.navy.mil

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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.