EXOSAT observations of X 1822-371 : modelling of the accretion disc rim.

Abstract

Data from three Exosat observations have been used to model X1822-371 as an X-ray emitting accretion disk corona (ADC) which is partially obscured by an optically emitting disk whose height varies with azimuthal angle. Using a system inclination of 85 + or - 3 deg and a disk structure parameterized by as few as two straight lines, the model is able to reproduce simultaneously both the X-ray and optical light curves of the binary system. The results are used to obtain absolute sizes of the X-ray and optical emitting regions, and have determined that the 5.57-hr period of X1822-371 is increasing on a time scale of 1.8 x 10 to the 6th yr. It is suggested that the X-ray obscuring material within the disk does not lie at a similar radius to that of the X-ray emitting ADC, but instead lies at the outer edge of the accretion disk.