  We have re-analyzed archival GINGA data of the soft X-ray transient source
GS2023+308 (V404 Cyg) covering the decline phase of its May 1989 outburst. Our
spectral modelling includes the relativistically smeared Compton reflected
continuum and iron K\alpha fluorescent line near 6.5 keV produced by X-ray
illumination of the accretion disc. This gives a powerful diagnostic of the
accretion geometry, with the amplitude of the reprocessed components showing
the solid angle subtended by the disc, while the detailed shape of the
relativistic smearing shows how close this material is to the black hole event
horizon.
  We find that reflection is always significantly present in the spectra, but
that its fractional contribution decreases as the decline progresses. The
amount of relativistic smearing is also consistent with decreasing during the
decline, although this is poorly constrained except for the brightest spectra.
One plausible scenario explaining this evolution is of an optically thick disc
with inner radius increasing as a function of time, with the X-ray source in
the form of a central corona. This is similar to the evolution inferred for
other X-ray transient sources, such as Nova Muscae, except that the underlying
power law spectrum of GS 2023+338 stayed constant as the disc geometry changed.
This challenges the underlying assumption of almost all models for the spectra
of accreting black holes, namely that the hard X-rays are formed by
Comptonization of seed photons from the accretion disc.
