Characteristics of the Cen X-3 neutron star from correlated spin-up and X-ray tics luminosity measurements .

Abstract

Results are presented of one month of observations with the ESA COS-B satellite of the X-ray pulsation period of Cen X-3, together with X-ray luminosity measurements during this same time.

The data are shown to be compatible with an unbraked spin-up by accretion from a Keplerian disk onto a neutron star with f = 4μ^2/7₃₀R^6/7₄₅(M/M_sun)-3/7 = 1.65 ± 0.44 and no braking occurring down to a luminosity of L_x = 4.2₁₀37 erg/s. The mean intrinsic luminosity during an observed turn-on episode is calculated from the high observed spin-up as L_x = (9.0 ± 2.6)₁₀37 erg/s, which together with the long term behaviour of the pulsation period shows that certain low states of the source are in fact periods of high accretion.

It is argued that some current neutron star models are irreconcilable with the value off determined in this paper. The present f determination is shown to imply a lower mass limit for the Cen X-3 neutron star of 1.1 M_sun.