Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...613..517l&link_type=abstract
The Astrophysical Journal, Volume 613, Issue 1, pp. 517-521.
Astronomy and Astrophysics
Astronomy
16
Stars: Binaries: Close, Stars: Individual: Constellation Name: Hercules X-1, Stars: Neutron, X-Rays: Binaries
Scientific paper
An accretion column model is applied to reproduce the pulse shape of Her X-1. The motivation for the model is the observed 35 day sequence of pulse shape changes, which imply a pencil beam from the near pole and a fan beam from the far pole. The pulse shape depends on the beam pattern, which is calculated for an emitting surface in the shape of a filled cone. The calculation has a parameterized emissivity function and includes gravitational light-bending and shadowing effects. Least-squares fitting of the model to the observed pulse profile yields best-fit parameters and statistical uncertainties for the viewing geometry, the geometry of the accretion column, and the mass-to-radius ratio of the neutron star. The derived mass-to-radius ratio is 0.121-0.128 Msolarkm-1 (3 σ statistical range). Combined with the mass determined from analysis of the orbit of Her X-1, several recent equations of state for dense matter are excluded for the neutron star in Her X-1.
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