X-ray observations of the 50-min dipping source XB1916-053

Three EXOSAT observations of the low-mass X-ray binary XB1916-053 have revealed extreme variability in the appearance of the dips, ranging from complete absence to two broad, deep dips per 50-min cycle. These dips are believed to result from the obscuration of the central X-ray source by azimuthal structure in the accretion disc; the data suggest that the dips, and thus the disc structure, evolve on a time-scale of hours. The absence of eclipses constrains the orbital inclination of the system to be ι < 790, thus requiring the vertical angular extent of the disc structure to be > 110. (author)