The Distance, Mass, and Radius of the Neutron Star in 4U 1608-52 - AstrophysicsReport as inadecuate

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Abstract: Low mass X-ray binaries that show thermonuclear bursts are ideal sources forconstraining the equation of state of neutron star matter. The lack ofindependent distance measurements for most of these sources, however, preventsa systematic exploration of the masses and radii of the neutron stars, hencelimiting the equation of state studies. We present here a measurement of thedistance to the low mass X-ray binary 4U 1608-52 that is based on the study ofthe interstellar extinction towards the source. We first model the individualabsorption edges of the elements Ne and Mg in the high resolution X-rayspectrum obtained with XMM-Newton. We then combine this information with ameasurement of the run of reddening with distance using red clump stars anddetermine a minimum distance to the source of 3.9 kpc, with a most probablevalue of 5.8 kpc. Finally, we analyze time-resolved X-ray spectra of Type-IX-ray bursts observed from this source to measure the mass and the radius ofthe neutron star. We find a mass of M = 1.74 +- 0.14 M sun and a radius of R =9.3 +- 1.0 km, respectively. This mass and radius can be achieved by severalmulti-nucleon equations of state.

Author: Tolga Guver, Feryal Ozel, Antonio Cabrera-Lavers, Patricia Wroblewski


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