Abstract

Flares with fine-structured features in their time profiles are of a special interest as sub-second time structures are attributed to processes of primary energy release. Using two-frequency microwave data recorded by the SSRT (5.7~GHz) and the Nobeyama Radioheliograph (17~GHz) together with X-ray data, we have comprehensively studied two flares with sub-second emission pulses (September~6, 1992 and November~2, 1992) and have started with two more (September~7, 1992 and March~3, 1994). In all four flares the impulsive sources found at 5.7 and 17~GHz coincided with the main sources of the burst continuum observed at these frequencies.