  Results are reported for analysis of the extensive Rosat observation of the
dipping low mass X-ray binary XB 1916-053. Dipping is 100% deep showing that
the emission regions are completely covered by the absorber. A good fit to the
non-dip spectrum is obtained using a model consisting of a blackbody with kT_BB
= 1.95 +0.74 -0.34 keV and a power law with photon index 2.32 +/- 0.04. These
components are identified with emission from the neutron star, and Comptonized
emission from an extended accretion disk corona (ADC). Dip spectra are
well-fitted by rapid absorption of the blackbody, and progressive covering of
the extended component, as the absorber moves across the source, with a
covering fraction that increases smoothly from zero to ~1.0. Progressive
covering shows that the Comptonized emission region is extended, consistent
with it originating in the accretion disk corona. The strong unabsorbed
component in the dip spectra is well-modelled as the uncovered part of the
Comptonized emission at all stages of dipping. There is no detectable change in
the low energy cut-off of the spectrum in dipping which supports the
identification of the unabsorbed part of the spectrum with the uncovered part
of the ADC emission. The absorbed part of the ADC emission is rapidly removed
from the 0.1 - 2.0 keV band of the PSPC, which therefore selects only the
uncovered part of the emission, and so the spectral evolution in dipping as
viewed by the PSPC depends only on the covering fraction, determined by the
geometric overlap between the source and absorber.
