Program

Mass, radius, surface gravity and gravitational redshift determination for the neutron star in the Xray burst source MXB 172834
Agnieszka Majczyna
Warsaw University Observatory (Warsaw, Poland)
Abstract:
We analyse archival Xray spectra of MXB 172834 obtained in 199699 by the instrument PCA on board of the RXTE satellite. Xray spectra were fitted to our extensive grids of model atmosphere spectra to determine the effective temperature T_{eff} on the neutron
star surface, logarithm of surface gravity log(g), and the gravitational redshift z simultaneously. We have chosen fitting by numerical model spectra plus broad gaussian line, modified by interstellar absorption and
the absorption on dust. We arbitrarily assume either hydrogenhelium chemical composition of a model atmosphere, or HHeFe mixture in solar
proportion. The best values of log(g), and
z were subsequently used to determine mass and radius of the neutron star. We obtained the best values of the parameters for the neutron star in Xray burst source MXB 172834: mass either M=0.52 or 0.64 M_{sol} (for HHe or HHeFe models, respectively), radius
and R=5.7 or 5.8 km, log(g)=14.4 or 14.5 and the gravitational redshift z=0.17 or 0.22. Confidence limits are rather large, however, they strongly support the equation of state for strange matter.
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