Dust scattering in the high-state eclipse of Cen X-3

EXOSAT data from two high-state eclipses of Cen X-3 are analysed for the effects of dust scattering. The light curves show bright (2 per cent of the out-of-eclipse flux), smoothly varying emission which reaches its minimum after mid-eclipse. Of this emission, the soft flux falls monotonically with orbital phase. We identify this soft component with dust scattering, and fit spectral models to the asymmetric emission, that is, to spectra obtained by subtracting from a spectrum at a given orbital phase before phase zero the corresponding spectrum from the equal and opposite phase after phase zero. We find that the model of Molnar & Mauche, used to fit dust scattering in Cyg X-3, can explain the observed spectra and yields values for the distance to Cen X-3 and for the size of the dust grains of 5.4 kpc and 0.33 μm, consistent with previous observations in other wavebands.