SOLAR SIMPLE BURSTS OBSERVED WITH HIGH-SPECTRAL-RESOLUTION IN THE 18-23 GHZ RANGE

For the first time, solar bursts in the frequency range of (18-23) GHz have been observed with high-time (0.6-1.2 s) and high-frequency reso lution (1 GHz), by using the Itapetinga 13.7 m diameter antenna. Here, we investigate the microwave type ''simple low level (< 10 SFU) burst s'' associated with the impulsive phase of solar flares. Observed prop erties of these simple bursts are: rise time t(r) similar to 3 s, deca y time t(d) similar to 5 s and spectral index ranging between -1 and - 4. These bursts were found to be associated with SF or SN flares as se en in H alpha. The above properties suggest that they are likely to be a microwave counterpart of elementary flare bursts. In the majority o f the cases,the spectral evolution is soft-hard-soft. This suggests a nonthermal gyrosynchrotron mechanism for generating these elementary f lare bursts. Estimated parameters of these simple burst sources are he ight (h similar to 2400 km), electron density (N-epsilon < 8.8 x 10(9) cm(-3)), and magnetic held (B similar to 300 G).