The limb flare of November 2, 1992: Physical conditions and scenario

The powerful X9 class flare was investigated using interferometric data of Nobeyama Radioheliograph (17 GHz) and SSRT (5.7 GHz). According to images obtained in circular polarization, it was found that the microwave burst was generated consequently in the sites, where opposite magnetic loops were in the close contact. Steady exponential growth of the total microwave flux in the initial stage of the flare under significant reconstruction of the radio sources certifies that the development of the flare was conducted by some large-scale instability. Radiation during the impulsive phase was produced by gyrosynchrotron emission of electrons trapped within a wide dome-like volume with B similar or equal to 300 G and n 2 10(10) cm(-3) In the decay phase, the emission at higher frequencies was mainly produced by bremsstrahlung from high loops emitting soft X-rays. There is evidence of the energy release long after the impulsive phase: an intensive, rather compact microwave source in the locus of contact of two oppositely polarized regions in these loops and sub-bursts during 2 hours after the peak at low heights. For the first time, a compact source of the sub-second pulses at 17 GHz was found to be located as high as 15 10(3) km. They were due to gyrosynchrotron emission.