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GR: Fachverband Gravitation und Relativitätstheorie

GR 11: Relativistic Astrophysics

GR 11.2: Vortrag

Mittwoch, 18. März 2015, 16:30–16:50, H 2013

Constraining the Equation-of-State of Neutron Stars by Phase-Resolved X-ray Spectroscopy — •Ralph Neuhaeuser and Valeri Hambaryan — AIU, U Jena, Schillergäßchen 2, 07745 Jena, Germany

We use XMM X-ray observations of the isolated neutron stars RBS1213, RXJ1856, and RXJ0720 to measure their compactness by X-ray phase resolved spectroscopy. These objects are also called Magnificent Seven Neutron Stars. They are isolated in the sense that they neither have a supernova remnant nor any known companions. They are on the order of 1 Myr old, X-ray bright, optically faint, nearby (on the order of one to few 100 pc), and show fast proper motion. We use many XMM light curves for different energy bands and many spectra of different light curve phases. Our model assumes a thin highly magnetized atmosphere above a solid state surface with a warm surface for optical emission and two hot emitting areas near the magnetic poles for the X-ray emission. Among the free fit parameters of our model is the gravitational redshift, which is directly related to the compactness M/R (mass M and radius R). We have determined the compactness for all three objects and compare them with predictions from different equations-of-state. In addition, for at least one of the three objects RXJ1856, the distance and radius is known, so that compactness and radius can yield the true mass. This might be the first neutron star with known mass and radius. We will also discuss how to improve on the error budget.