AAS 204th Meeting, June 2004
Session 74 Stellar Leftovers
Poster, Thursday, June 3, 2004, 9:20am-4:00pm, Ballroom

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[74.18] Mass-Radius Constraint for the Neutron Star in Her X-1

D.A. Leahy (University of Calgary)

A parametrized emission model is fitted to the observed pulse shape of Her X-1. The observed 35-day sequence of pulse shape changes for Her X-1 imply a pencil beam from the near pole and a fan beam from the far pole, which can be obtained with cone-shaped emission surfaces (Leahy,D., 2004, MNRAS,348,932). Beam patterns are calculated using a parametrized emissivity function and include gravitational light-bending and shadowing effects. Least-squares fitting to the observed pulse shape yields best fit parameters and uncertainties for the viewing geometry, the geometry of the accretion column and for the mass to radius ratio of the neutron star. The derived limits on mass to radius ratio are 0.121 to 0.128 M\odot/km (3\sigma range). Combined with mass limits from an orbit of analysis Her X-1, several recent equations of state for dense matter can be excluded for the neutron star.

This work supported by the Natural Sciences and Engineering Research Council of Canada.

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