Constraining Neutron Star Masses and Radii Using High Resolution Spectra

Feryal Ozel

University of Arizona


While recent X-ray missions provide us with high resolution spectra of thermally emitting neutron stars, the largest uncertainties in determining neutron star masses and radii from from these spectra are still theoretical. In order to obtain accurate constraints, (i) the surface layers of neutron stars need to be modeled in detail, (ii) the effects of strong gravity and rotation on surface emission need to be taken into account, and (iii) possible temperature non-uniformity and unknown emission geometry need to be addresses. In this talk, I will discuss recent models of neutron star surface layers and the general relativistic effects on the surface, pointing out the uncertainties in mass-radius determination arising from each. I will then show how combining timing information of neutron stars with their spectra reduces greatly the uncertainties arising from general relativistic and geometrical effects. Finally, I will discuss how combining several different spectral and timing measurements of X-ray sources provides us with complementary and the most promising method for accurate determination of neutron star masses and radii, as well as minimizes observational uncertainties such as source distances.

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