By Agnieszka Majczyna

The goal of our work was to determine the precision of mass and radius determination of neutron stars based on spectra to be obtained with the Athena/WFI instrument. Due to a lack of real Athena observations, we simulated three spectra using publicly available WFI calibration files. We constructed three fake spectra A, B and C corresponding to three different values of effective temperature, surface gravity, and redshift. We assume also the observed fluxes of a few hundredths of the Crab (~10¹⁰ erg cm^-2s^-1). Next, we fitted these fake spectra with a large grid of our theoretical spectra. In this procedure, we determined effective temperature, the logarithm of the gravity and gravitational redshift for each of our fake spectrum. Obtained values of the gravity and gravitational redshift were converted into mass and radius of the neutron star.

In each case, we determined the precision of the measurements with errors in the range of 3%-10% for mass and 2%-8% for radius within 1σ confidence. All errors (1σ) are relatively small for the Athena/WFI detector. We note that the errors defined by 2σ confidence ranges are in the range of 11%-17%. Therefore, we demonstrated that our method will allow us to constrain the EOS of the dense matter of neutron stars using future observations of the Athena mission.

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