GRANAT / SIGMA observation of the early afterglow fromGRB 920723

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 af-terglow where ux 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 uctuations. 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 uxes corresponds to the power law spectral index = 0:0 ? 0:3. At t = 6 s, the value of increases to 1 and stays at this level af-terwards. The observed afterglow characteristics are discussed in connection with the relativistic reball model of gamma-ray bursts.