A comparison of the optical and microwave emissions of some major solar flares

Abstract

In the first part of the paper, we study the relations between the frequency of maximum radio flux f,n~, and the magnetic field strength at the photosphere B o and between the maximum radio flux Fmax and the field and its scale L for two differing flares occurring above very different photospheric conditions. It is shown that the simple relations predicted by the gyro-synchrotron emission mechanism [,,a~ ~ Bp and Fm~x ~ B2L 2 account for the fact that the flares produced microwave bursts of about the same Fmax, but of differing f m~,.The spectra of type IVp. radio bursts associated with three large proton flares with post-flare loops have been analyzed. It is found that the decimetric peak vanishes with the onset of the first optical loops. This is consistent with the model of Kopp and Pneuman (1976) which associates growing systems of loops with gradual fieldline reconnection above flaring regions.

THE CONTRIBUTION OF MICROBUNCHING INSTABILITY TO SOLAR FLARE EMISSION IN THE GHz TO THz RANGE OF FREQUENCIES

“…A number of solar bursts have been observed to have unexpected distinct spectral components in the gigahertz to subterahertz range: one corresponds to the well-known microwave emission maximizing at a few to tens of gigahertz and another with fluxes increasing for larger sub-terahertz frequencies. Early solar burst observations made up to 0.1 THz have suggested high-frequency "double-spectral" features (Shimabukuro 1970;Croom 1971;Akabane et al 1973;Zirin & Tanaka 1973;Roy 1979;Kaufmann et al 1985;White et al 1992). Observations carried out at higher frequencies (0.2 and 0.4 THz) by the Solar Submillimeter Telescope (SST) have clearly evidenced the subterahertz flux component increasing with frequency (Kaufmann et al 2004(Kaufmann et al , 2009Kaufmann 2011;Silva et al 2007).…”