Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20915913w&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #159.13; Bulletin of the American Astronomical Society,
Astronomy and Astrophysics
Astronomy
Scientific paper
Recent work by Becker and Wolff on spectral formation in X-ray pulsar accretion columns has established a novel physical theory from first principles that reproduces the observed X-ray spectra for several well-known sources. In the analytical approach of Becker and Wolff, an approximate velocity profile was employed in order to separate the transport equation. This resulted in a closed-form solution for the emergent photon spectrum describing the reprocessing of seed photons created via bremsstrahlung, cyclotron, and blackbody emission. The good agreement between the analytical solution and the observational data is encouraging, but it is not clear how the utilization of the approximate velocity profile affects the accuracy of the solution. In this paper we employ a numerical approach to solve the transport equation based on the exact velocity profile describing the inflow of the gas in the accretion column. When the exact velocity profile is employed, the transport equation is no longer separable, and therefore we employ a relaxation method to solve for the spectrum of the escaping radiation as a function of energy and altitude in the column. The results are compared with the observational data and also with the spectra computed using the analytical model of Becker and Wolff. We conclude by discussing future enhancements of the simulation code such as including (i) a self-consistent calculation of the electron temperature based on inverse-Compton equilibrium, (ii) the vertical variation of the magnetic field strength and the column cross section, and (iii) the energy and angle dependence of the electron scattering cross section.
Becker Peter A.
Wolff Michael Thomas
Wolfram Kenneth D.
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