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Preprint 12/06

Non-LTE Models for Neutron Star Atmospheres and Supernova-Fallback Disks

K. Werner (1), T. Nagel (1), T. Rauch (1), V. Suleimanov (1,2)

(1) Institut für Astronomie und Astrophysik, Tübingen, Germany
(2) Kazan State University, Kremlevskaja Str., 18, Kazan 420008, Russia

To be published in: Advances in Space Research

Abstract. We describe our recent progress in modeling supernova-fallback disks and neutron star (NS) atmospheres.
We present a first detailed spectrum synthesis calculation of a SN-fallback disk composed of iron. We assume a thin disk with a radial structure described by the alpha-disk model. The vertical structure and emission spectrum are computed self-consistently by solving the structure equations simultaneously with the radiation transfer equations under non-LTE conditions. We describe the properties of a specific disk model and discuss various effects on the emergent UV/optical spectrum.
We investigate Compton scattering effects on the thermal spectrum of NSs. In addition, we constructed a new generation of metal line-blanketed non-LTE model atmospheres for NSs. It is compared to X-ray burst spectra of EXO0748-676. It is possible that the gravitational redshift, deduced from absorption lines, is lower (z=0.24) than hitherto assumed (z=0.35). Accordingly, this would result in NS mass and radius lower limits of M>1.63 Msun and R>13.8 km.

Preprint (449 kb PDF file including figures)

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