Speaker
Description
Neutron star masses and radii are observational tracers of the equation of state of cold dense matter.
One way to determine them is to model the thermal X-ray spectra of neutron stars. Here we present the results obtained by modeling the X-ray spectrum of a neutron star at the center of supernova remnant HESS J1731-347, the distance to which is 2.5(3)\,kpc, known from measurements by the Gaia astrometric observatory. Pulsations of the X-ray flux of the source were not detected at a level of 8\%. Therefore, for the theoretical description of the X-ray spectrum, it was assumed that the magnetic field of the star is absent, the surface of the star is homogeneous, covered with a carbon envelope, and its spectrum is described by the spectrum of a purely carbon model atmosphere. As a result, it was found that the mass and radius of the neutron star are unexpectedly small, 0.77$^{+0.20}_{-0.17}$ solar masses, and 10.4$^{+0.86}_{-0.74}$ km, respectively. Descriptions of the observed spectrum by models with a non-uniform surface and parameters typical for neutron stars, possible due to the not very strong constraint on the flow pulsations, are also discussed.
