  We present a GRANAT/SIGMA observation of the soft gamma-ray afterglow
immediately after GRB 920723. The main burst is very bright. After ~6 s, the
burst light curve makes a smooth transition into an afterglow where flux decays
as t^{-0.7}. The power-law decay lasts for at least 1000 s; beyond this time,
the afterglow emission is lost in the background fluctuations. At least ~20% of
main burst energy is emitted in the afterglow. At approximately ~6 s after the
trigger, we also observe an abrupt change in the burst spectrum. At t<6 s, the
ratio of 8-20 and 75-200 keV fluxes corresponds to the power law spectral index
\alpha=0.0-0.3. At t=6 s, the value of \alpha increases to \alpha= ~1 and stays
at this level afterwards. The observed afterglow characteristics are discussed
in connection with the relativistic fireball model of gamma-ray bursts.
