Search for extended hard?-ray emission in GRB's

The PHEBUS instrument aboard the GRANAT observatory is able to record spectra of gamma-ray bursts in a broad energy range from 0.1 to 100 MeV. Over 180 bursts were observed by PREBUS during five years of operation. They represent a very rich sample of events widely differing in durations, light curves and energy spectra. The problem of burst behaviour in the decay phase of the GRB events is discussed in this paper. We present here the results of the search for emission from GRB sources in 100 keV - 100 MeV range after the main burst has finished. Presence of extended emission was found in about 10% of the gamma-ray bursts detected by PHEBUS.