1 Introduction

Fast and accurate localizations of gamma-ray bursts by BeppoSAX helped to establish the connection of GRB with the decaying X-ray, optical, and radio sources. These observations are well explained by the relativistic fireball model (e.g. Sari et al. 1998). The fireball observations immediately after the burst, when the Lorenz factor, temperature and density are at maximum, are of great interest. Unfortunately, afterglows observations earlier than $\approx 10$ hours after the burst were impossible.

We present GRANAT/SIGMA observation of the GRB 920723 light curve revealing a soft gamma-ray afterglow with flux decaying as a power law $\sim t^{-0.7}$which starts immediately after the main burst and lasts for at least 1000 s.